ageing is a natural process essay

The Concept of Aging Process Essay

Introduction.

The aging process is an inevitable part of human existence and all individuals who live to grow old, experience this process. The science dealing with the process of aging is termed ‘gerontology’ and this science tries to elucidate the factors and details of the process of aging. Gerontology is thus associated with the elderly and the physical and psychological changes which occur in their bodies, due to old age.

However, this process may not be uniform for all persons and there may be variations in the aging process of individuals, depending on the lifestyle and diet. The aging process is also highly impacted by hereditary factors and it is interesting to note that while some individuals may age faster, others may not show signs of aging at the same pace, nevertheless, the basic signs of aging are apparent among a majority of elderly persons.

Many of the elderly persons above the age of sixty-five years have the “activity of daily living limitation” disability, while a percentage of three percent is completely disabled. Many chronic diseases including hypertension, diabetes, arthritis and hearing problems, and heart problems are commonly prevalent in the elderly (Aging America, 1985-86).

As people age, they begin to give less attention to their health and well-being, which sometimes results in severe problems at the physical and psychological levels. Growing old and aging is a natural process of the human body and one which is inevitable. Thus, there are innumerable changes that take place in the body which lead to degradation of health. This science which deals with the aging process of getting old is termed gerontology.

As people grow older, there is deterioration in their health, and sometimes the wrong diets and activities can lead to further degradation in their health leading to several deficiency diseases. The most visible changes which occur among the elderly are the sagging of skin and loss of hair. Skin pigmentation could also result in a change of skin color.

With the increase in age, they sometimes tend to exercise less, which also reduces their rate of metabolism and could also result in weight gain. The gain in weight initiates many problems, with the reduced level of immunity in the weak bodies of the elderly.

The aging process brings about internal bodily changes that also occur in the bodies and the bones of the elderly become fragile, due to the loss and insufficiency of calcium in their bodies. This commences physical problems like degeneration of the bones and subsequent problems like fractures.

Certain other changes also occur in the bodies of the aging adults including a loss in eyesight and hearing abilities. Cataracts and glaucoma are some of the common eye problems faced by aging elderly persons. Loss of vision is also more common among the older populations.

Internal organs also undergo many changes in elder persons. Organs like the kidney and the bladder lose their propensity to function well and this causes many health problems among them.

The lack of an optimal diet and exercise also tends to cause an increase in the fat deposits in the blood vessels of the elderly which puts them at an additional risk of ‘coronary artery disease’ more commonly known as heart disease. The ability of the respiratory system also reduces which leads to breathing problems.

The U.S. Select Committee on Aging (1988) has confirmed that in the past two decades there has been a phenomenal rise in the older population in the United States of America, which is further estimated to grow by seven times as compared to its current size by the year 2050. This substantial rise in the elderly population is believed to create a rise in the demand for caregiving services to this relatively frail and dependant populace.

According to several researchers, the primary reasons for this change in trend is attributed to an increase in the overall percentage of women working outside their homes and their participation in the labor force, along with other factors such as (Montgomery & Borgatta, 1989; Wisendale & Allison, 1988). Although there are many formal caregiving services present for the elderly population, the family members continue to be the prime caregivers to nearly eighty percent of the older populace of the U.S. (Pilisuk & Parks, 1988). Thus we can conclude that aging is an inevitable aspect of human lives and a phase during which the elderly people need additional care and support due to their deteriorating health and Gerontology is the branch that deals with all the issues related to the aging process and old age.

Aging Americans: Trends and Projections (1986 ed.). Washington, DC: U.S. Department of Health and Human Services.

Blieszner, R., & Alley, J. M. (1990). Family caregiving for the elderly: An overview of resources. Family Relations, 39(1), 97-102.

Montgomery, R. J. V., & Borgatta, E. F. (1989). The effects of alternative support strategies on family caregiving. The Gerontologist, 29(4), 457-464.

Pilisuk, M., & Parks, S. H. (1988). Caregiving: Where families need help. Social Work, 33(5), 436-440.

U.S. Select Committee on Aging. (1988). Exploding the myths: Caregiving in America. (Comm. Pub. 100-665). Washington, DC: U.S. Government Printing Office.

Wisendale, S. K., & Allison, M. D. (1988). An analysis of 1987 state family leave legislation: Implications for caregivers of the elderly. The Gerontologist, 28(6), 779-785.

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Aging: A Natural and Beneficial Part of Life

Aging is a highly individualized experience and age-related changes occur at different rates for different people. The functional status between individuals of the same chronological age can be surprisingly different. Research suggests that some individuals report feeling up to 20 percent younger than their chronological age. 

Aging Is a Natural Process

The aging process is a very natural one. It begins at conception and continues throughout the life cycle. The way someone ages depends on heredity, physical health, nutrition, mental health, and other unknown factors. Some scientists feel that human beings have a built-in “biological clock” which would run for 130 years if no diseases or illnesses affected the body.

Negative Perceptions

Many people have negative assumptions about aging, including beliefs that older people automatically become incompetent, experience depression, lose their memory, and are unable to enjoy life. Such stereotypes develop in us at a very young age and continue to influence us into our adult lives. Therefore, those nearing the age of 65 tend to become anxious about their health care, finances, and physical functioning. Negative perceptions of aging are often internalized and can even lead to serious health consequences. Examples include a greater risk of developing Alzheimer’s Disease (which causes problems with memory and thinking), impaired physical functioning, and even premature death. Alternatively, having positive perceptions about aging can lead to health benefits and may even add years onto one’s life.

Benefits of Aging

Comparatively better health .

Studies show that in the last 50 years, the health status of older adults has improved. There is even evidence that a large percentage of those age 65 and older have the same physical and mental capabilities as those who are much younger. Eating healthy and being active are two important factors that can delay some age-related diseases and conditions, which is crucial to living a long and healthy life.

Significant personal growth

According to Erik Erikson, who was a developmental psychologist, middle and late adulthood are significant times of personal growth. Erikson was best known for his theory of psychosocial development, which refers to how a person’s needs coincide with the needs of society. This theory stated that there are eight stages in a person’s life in which their personality develops. The last two stages concern middle-aged and older adults, specifically ages 40 and over. 

The eighth stage takes place when one reaches 65 years old and ends at death. This stage is called “integrity versus despair” and is characterized as the stage of reflection. When life has slowed down and productivity has decreased, we look back on our lives and contemplate our accomplishments and achievements. The successful completion of this stage leads to a virtue of wisdom, which helps one to reflect on their life and feel proud of what they have accomplished. People who look back on their lives and regret not achieving their goals experience feelings of despair rather than integrity. Most people alternate between feelings of integrity and despair during this last stage.

Aging is a natural and beneficial part of life. Perhaps the American poet Henry Wadsworth Longfellow sums up the aging experience best: “For age is opportunity no less/ Than youth itself, though in another dress,/ And as the evening twilight fades away/ The sky is filled with stars, invisible by day.”

Chopik, W.J., Bremner, R.H., Johnson, D.J., & Giasson, H.L. (2018, February 1). Age Differences in Age Perceptions and Developmental Transitions. Frontiers in Psychology, 9(67). doi-org.proxy.lib.ohio-state.edu/10.3389/fpsyg.2018.00067

Fullen, M.C., Granello, D.H., Richardson, V.E., & Granello, P.F. (2018, January 12). Using Wellness and Resilience to Predict Age Perception in Older Adulthood. Journal of Counseling & Development, 96(4), 424-435. doi-org.proxy.lib.ohio-state.edu/10.1002/jcad.12224

Hawkley, L.C., Norman, G.J., & Agha, Z. (2019, January 16). Aging Expectations and Attitudes: Associations with Types of Older Adult Contact. Research on Aging, 41(6), 523-548. doi-org.proxy.lib.ohio-state.edu/10.1177/0164027518824291

Hung, C., Azofeifa-Navas, J., Tan, H., Hu, C.A., & Clarke, N. (2015, March 10). Aging: Mitigation and Intervention Strategies. BioMed Research International. dx.doi.org/10.1155/2015/276539

Lewis, R. (2020, April 28). Erikson’s 8 Stages of Psychosocial Development, Explained for Parents. Parenthood. healthline.com/health/parenting/erikson-stages

McLeod, S. (2018). Erik Erikson’s Stages of Psychosocial Development. Simply Psychology. simplypsychology.org/Erik-Erikson.html

O’Brien, E.L., & Sharifian, N. (2019, April 11). Managing expectations: How stress, social support, and aging attitudes affect awareness of age-related changes. Journal of Social and Personal Relationships, 37(3), 986-1007. doi-org.proxy.lib.ohio-state.edu/10.1177/0265407519883009

Olshansky, S.J. (2015, April 1). The Demographic Transformation of America. Daedalus, 144(2), 13-19. doi.org/10.1162/DAED_a_00326

Soto-Perez-de-Celis, E., Li, D., Yuan, Y., Lau, Y.M., & Hurria, A. (2018, June). Functional versus chronological age: geriatric assessments to guide decision making in older patients with cancer. The Lancet Oncol, 19(6), e305-e316. doi.org/10.1016/S1470-2045(18)30348-6

Adapted from the fact sheet When Does Someone Attain Old Age by Linnette Mizer Goard, Extension Agent, Ohio State University Extension, 1996  

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Overview of Aging

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Aging is a gradual, continuous process of natural change that begins in early adulthood. During early middle age, many bodily functions begin to gradually decline.

People do not become "older" or "elderly" at any specific age. Traditionally, age 65 has been designated as the beginning of older age. But the reason was based in history, not biology. Many years ago, age 65 was chosen as the age for retirement in Germany, the first nation to establish a retirement program. In 1965 in the United States, age 65 was designated as the eligibility age for Medicare insurance. This age is close to the actual retirement age of most people in economically advanced societies.

When a person becomes an older adult can be answered in different ways:

Chronologic age is based solely on the passage of time. It is a person’s age in years. Chronologic age has limited significance in terms of health. Nonetheless, the likelihood of developing a health problem increases as people age, and it is health problems, rather than normal aging, that are the primary cause of functional loss during older age. Because chronologic age helps predict many health problems, it has some legal and financial uses.

Biologic age refers to changes in the body that commonly occur as people age. Because these changes affect some people sooner than others, some people are biologically older at 65, and others not until a decade or more later. However, most noticeable differences in apparent age among people of similar chronologic age are caused by lifestyle, habit, and subtle effects of disease rather than by differences in actual aging.

Psychologic age is based on how people act and feel. For example, an 80-year-old who works, plans, looks forward to future events, and participates in many activities is considered psychologically younger.

Most healthy and active people do not need the expertise of a geriatrician (a doctor who specializes in the care of older adults) until they are 70, 75, or even 80 years old. However, some people need to see a geriatrician at a younger chronologic age because of their medical conditions.

Normal aging

People often wonder whether what they are experiencing as they age is normal or abnormal. Although people age somewhat differently, some changes result from internal processes, that is, from aging itself. Thus, such changes, although undesired, are considered normal and are sometimes called "pure aging." These changes occur in everyone who lives long enough, and that universality is part of the definition of pure aging. The changes are to be expected and are generally unavoidable. For example, as people age, the lens of the eye thickens, stiffens, and becomes less able to focus on close objects, such as reading materials (a disorder called presbyopia ). This change occurs in virtually all older adults. Thus, presbyopia is considered normal aging. Other terms used to describe these changes are "usual aging" and "senescence."

Did You Know...

Exactly what constitutes normal aging is not always clear. Changes that occur with normal aging make people more likely to develop certain disorders. However, people can sometimes take actions to compensate for these changes. For example, older adults are more likely to lose teeth. But seeing a dentist regularly, eating fewer sweets, and brushing and flossing regularly may reduce the chances of tooth loss. Thus, tooth loss, although common with aging, is an avoidable part of aging.

Also, functional decline that is part of aging sometimes seems similar to functional decline that is part of a disorder. For example, with advanced age, a mild decline in mental function is nearly universal and is considered normal aging. This decline includes increased difficulty learning new things such as languages, decreased attention span, and increased forgetfulness. In contrast, the decline that occurs in dementia is much more severe. For example, people who are aging normally may misplace things or forget details, but people who have dementia forget entire events. People with dementia also have difficulty doing normal daily tasks (such as driving, cooking, and handling finances) and understanding the environment, including knowing what year it is and where they are. Thus, dementia is considered a disorder, even though it is common later in life. Certain kinds of dementia, such as Alzheimer disease , differ from normal aging in other ways as well. For example, brain tissue (obtained during autopsy) in people with certain kinds of dementia looks different from that in older adults without the disease. So the distinction between normal aging and dementia is often clear.

Sometimes the distinction between functional decline that is part of aging and functional decline that is part of a disorder seems arbitrary. For example, as people age, blood sugar levels increase more after eating carbohydrates than they do in younger people. This increase is considered normal aging. However, if the increase exceeds a certain level, diabetes , a disorder, is diagnosed. In this case, the difference is one of degree only.

Healthy (successful) aging

Healthy aging refers to postponement of or reduction in the undesired effects of aging. The goals of healthy aging are maintaining physical and mental health, avoiding disorders, and remaining active and independent. For most people, maintaining general good health requires more effort as they age. Developing certain healthy habits can help, such as

Following a nutritious diet

Avoiding cigarette smoking and excessive alcohol use

Exercising regularly

Staying mentally active

The sooner a person develops these habits, the better. However, it is never too late to begin. In this way, people can have some control over what happens to them as they age.

Some evidence suggests that in the United States, healthy aging is on the rise:

A decrease in the percentage of people aged 75 to 84 who report impairments

A decrease in the percentage of people over age 65 with debilitating disorders

An increase in the oldest old—people age 85 and older, including those who have reached 100 (centenarians)

Studying Aging

Life expectancy.

The average life expectancy of Americans has been increasing dramatically over the past century. A male child born in 1900 could expect to live only 46 years, and a female child, 48 years. In 2021, the average life expectancy in the United States for the total population was 76 years. Although much of this gain can be attributed to the significant decrease in childhood mortality, life expectancy at every age beyond 40 has also increased dramatically. For example, a 65-year-old man can now expect to live to about age 83, and a 65-year-old woman, to about age 86. Overall, women live about 4 to 5 years longer than men. This difference in life expectancy between men and women has changed little, despite late 20th-century and early 21st-century changes in women’s lifestyle, including smoking more and experiencing more stress.

Despite the increase in average life expectancy, the maximum life span—the oldest age to which people can live—has changed little since records have been kept. Despite the best genetic makeup and healthiest lifestyle, the chance of living to be 120 is tiny. Madame Jeanne Calment had the longest documented lifespan: 122 years (1875 to 1997).

Several factors influence life expectancy:

Heredity: Heredity influences whether a person will develop a disorder. For example, a person who inherits genes that increase the risk of developing high cholesterol levels is likely to have a shorter life. A person who inherits genes that protect against coronary artery disease and cancer is likely to have a longer life. There is good evidence that living to a very old age—to 100 or older—runs in families.

Lifestyle: Avoiding smoking, not abusing illicit drugs and alcohol , maintaining a healthy weight and diet , exercising , and getting recommended vaccinations and screening examinations help people function well and avoid disorders.

Exposure to toxins in the environment: Such exposure can shorten life expectancy even among people with the best genetic makeup.

Health care: Preventing disorders or treating disorders after they are contracted, especially when the disorder can be cured (as with infections and sometimes cancer), helps increase life expectancy.

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

American Association of Retired People (AARP) : This resource focuses on issues pertaining to people 50 years of age and older (for example, health care, caregiving, and access to affordable, quality long-term care).

American Federation for Aging Research (AFAR) : This resource provides information about ongoing biomedical research dedicated to the support and advancement of healthy aging.

Benefits Check Up : This resource helps older adults find local benefits they may be eligible for.

Older Adult Health : This resource from the Centers for Disease Control and Prevention provides health statistics for Americans age 65 and older.

National Council on Aging and National Institute on Aging : These resources provide information for older adults regarding topics ranging from health care and nutrition to caregiving to research.

Administration for Community Living and National Association of Area Agencies on Aging : These resources provide information about independent living for older adults and people of all ages with disabilities.

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The Personal Experience of Aging, Individual Resources, and Subjective Well-Being

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Nardi Steverink, Gerben J. Westerhof, Christina Bode, Freya Dittmann-Kohli, The Personal Experience of Aging, Individual Resources, and Subjective Well-Being, The Journals of Gerontology: Series B , Volume 56, Issue 6, 1 November 2001, Pages P364–P373, https://doi.org/10.1093/geronb/56.6.P364

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The personal experience of aging, the resources relevant to it, and the consequences for subjective well-being were investigated in a sample of 4034 Germans aged 40 to 85. The data revealed 3 dimensions of aging experiences as particularly relevant: (a) physical decline, (b) continuous growth, and (c) social loss. Not only being younger but also having better subjective health, higher income, less loneliness, higher education, and greater hope were negatively associated with physical decline and social loss and positively associated with continuous growth. The number of children participants had played no role. All three dimensions of the aging experience were also found to be related to both positive and negative affect and, with the exception of physical decline, to life satisfaction.

Decision Editor: Toni C. Antonucci, PhD

THE awareness of age and the experience of growing older are inherent components of the self for most people in their adult years (George, Mutran, and Pennybacker 1980 ; Neugarten 1968 , Neugarten 1969 , Neugarten 1979 ; Peters 1971 ; Ryff 1991 ). As self-conceptions are found to play an important role in behavior and adaptive outcomes (Bandura 1986 ), this may also be assumed for the cognitions that an individual holds about his or her own aging process (Lerner and Busch-Rossnagel 1981 ; Markus and Herzog 1992 ; Ruth and Coleman 1996 ). In this article, the personal experience of aging is investigated as well as the factors that relate to it, along with the question of whether and how cognitions concerning one's own aging relate to indicators of subjective well-being.

In both literary and philosophical works and in phenomenological studies, the varied nature of the personal aging experience has been extensively described (e.g., Beauvoir 1970 ; Cicero, as in Baltes and Baltes 1990 ; Cole and Gadow 1986 ; Thompson 1992 ). The empirical investigation of the personal experience of aging, however, is approached almost exclusively from the perspective of subjective age identification or age identity. Subjective age identification refers to just how old a person feels or the age group with which the individual identifies him- or herself (Barak and Stern 1986 ; Baum and Boxley 1983 ; Goldsmith and Heiens 1992 ; Kastenbaum, Derbin, Sabatini, and Artt 1972 ; Markides and Boldt 1983 ; Ward 1977 ). Rather than the personal experience of aging, however, the foregoing research is largely concerned with the personal experience of age.

Also, some studies exist that clearly relate to the concept of the personal experience of aging, but that take a somewhat different perspective. The work of Heckhausen and colleagues, for instance, focuses on personal and normative conceptions about adult developmental change in psychological attributes. It was found that different age groups perceive development across the life span as the coexistence of gains and losses, but also as an increasing risk of decline and a decreasing potential for growth (Heckhausen, Dixon, and Baltes 1989 ; Heckhausen and Krueger 1993 ). Another example is the work on possible selves of Markus and colleagues. Possible selves are representations of individuals' ideas of what they might become in the future (Cross and Markus 1991 ; Markus and Nurius 1986 ; Ryff 1991 ). Possible selves are found to change across the life span, which may be interpreted as a component of the personal experience of aging.

Up until now, only a few studies have empirically examined the personal experience of aging framed in terms of aging. For instance, Keller, Leventhal, and Larson 1989 conducted in-depth interviews on the aging experience with 32 community-dwelling adults aged 50 to 80 years and identified five major categories of positive and negative experiences: (a) aging as a natural and gradual process without remarkable features, (b) aging as a period of life evaluation, philosophical reflection, or increased wisdom and maturity, (c) aging as a period of increased freedom, new interests, and fewer demands, (d) aging as a period associated with physical health difficulties or concerns about health, and (e) aging as a period of losses, both interpersonal and job related (Keller et al. 1989 ). Connidis 1989 also investigated the aging experience of 400 community-dwelling people older than the age of 65 by asking if they liked or disliked anything about being their age and if they had any worries about growing older. These people generally did not focus on the negative aspects of aging. When categorized into three groups of people holding a negative, a moderate, or a positive view of aging, however, those holding a negative view were older, in poorer health, and had fewer children than those holding a positive view. Compared with those holding a moderate view of aging, the people holding a negative view were also older, less financially secure, in poorer health, more likely to have never been married, and more likely to see aging as worse than expected (Connidis 1989 ).

The present article has three basic aims: first, to investigate the personal experience of aging in such a manner that a wide range of aging conceptions relating to the different domains of the individual's existence are considered; second, to identify those factors that appear to relate to the manner in which the personal process of aging is conceived. Actual age is obviously an important factor, but research has shown that other factors also play a role. Among these are subjective health, being married, income, and the number of children (Connidis 1989 ). The third and final aim is to investigate whether and how the personal experience of aging—as a cognitive part of the aging self-concept—relates to adaptive outcomes, that is, indicators of subjective well-being. Several studies have shown a positive relationship between age identity (feeling younger) and measures of adjustment among older adults (e.g., George et al. 1980 ; Montepare and Lachman 1989 ). Whether a similar relationship holds for the personal experience of aging and measures of adjustment is not as yet clear, however.

Three sets of expectations guided the empirical investigation. First, there are indications that the experience of aging concerns a number of different dimensions of life (Keller et al. 1989 ) and that it can be framed in both positive and negative terms (Connidis 1989 ). These findings fit with the life span theoretical perspective on the multidimensionality and multidirectionality of development and aging (Baltes 1987 ). We therefore hypothesized that the personal experience of aging would reflect different dimensions (be multidimensional), and it would be multidirectional in the sense that it would involve both positive and negative experiences. This kind of multidirectionality we refer to as weak multidirectionality, as opposed to strong multidirectionality, which is considered in the second set of hypotheses, below.

The second set of expectations guiding the present research concerns those factors that may play a role in the origin of personal conceptions of aging. Actual age is obviously an important factor, and strong multidirectionality would imply that, with increasing age, some aging experiences become more positive, whereas others become more negative (Baltes 1987 ). However, in line with identified age-related changes in conceptions of aging (Connidis 1989 ; Heckhausen et al. 1989 ) we hypothesized that strong multidirectionality would not obtain: With increasing age, the experience of aging will become less positive and more negative.

Next to age, other factors relating to individual circumstances or characteristics may also be implicated in the origin of personal conceptions of aging. Relevant factors can be derived from theories that postulate the importance of individual resources (physical and material, social, and psychological resources) for coping with life in general and the aging process in particular (Baltes and Lang 1997 ; Steverink, Lindenberg, and Ormel 1998 ). A stable and varied repertoire of resources allows people to not only acquire important goals, but also compensate for the losses that accompany the process of aging. The important physical and material resources for most people in middle and later adulthood are health and financial security: Adapting to the process of aging is generally easier when a person is healthy and without financial worries. The important social resources for most people in middle and later adulthood are having a spouse and children or family and close friends. The important psychological resources for most people in middle and later adulthood are not only their intellectual skills but also their beliefs about self-efficacy and personal agency or feelings of control. Still other resources may exist, but the resources mentioned here are among the most important ones for the majority of adult people. We therefore hypothesized that higher levels of resources will be related to feeling less negative and worried about growing older. That is, the person with more personal resources is better able to cope with life and the process of aging than is the person with less resources. We also hypothesized that the role of resources is stronger for the experience of aging than is actual age. On one hand, actual age is a rather "empty" variable simply reflecting the resources with which it correlates, such as health. On the other hand, actual age may be a very rough indicator of just how much time a person has to live and thereby clearly influences the experience of aging. Given that the amount of time left to live is rather uncertain for most adult people, however, it is hypothesized that the impact of actual age on the experience of aging will be relatively weaker than the impact of resources.

The final set of expectations concerns the generally supported positive relationship between younger age identity and adjustment (e.g., George et al. 1980 ; Montepare and Lachman 1989 ). We do not attribute this positive relationship to denial of aging (Montepare and Lachman 1989 ; Ward 1977 ), however, but to a complex set of relations involving cognitions, behavior, and adaptive outcomes (Bandura 1986 ; Markus and Herzog 1992 ). To reach or maintain a state of well-being across the course of life, individuals must make decisions that enhance their well-being. Decisions of this kind pertain to not only the ability to set goals but also the ability to delay on the rewards of desired outcomes. For instance, regaining the ability to walk after knee surgery requires not only painful effort and exercise, but also the capacity to set a distant goal. The ability to keep such a long-term goal in mind requires not only a delay of gratification but also positive expectations with regard to future outcomes. Whereas a positive expectation (walking again) can further motivate decisions (exercise) that enhance one's well-being, a negative or pessimistic expectation will undermine one's motivation to do the painful exercises needed to walk again. The cognitions concerning one's own aging process can refer to already lived experiences but also to (generalized) expectations with regard to the process of aging in the future. The hypothesis is therefore that people with a positive view or expectation with regard to their aging process will be better able to make the "right" decisions and thus experience higher levels of subjective well-being than will people with a negative view. Put differently, people with a negative view or expectation with regard to their own aging process will be inclined to make the "wrong" decisions and thereby experience low levels of subjective well-being.

Participants

The participants ( n = 4838) in the German Aging Survey (Dittmann-Kohli, Kohli, and Kunemund 1995 ) were between 40 and 85 years of age. They were identified through a national probability sampling of local authorities, both in East and West Germany and were stratified by age, gender, and living region (East or West Germany). The fieldwork was conducted during the first half of 1996. Fifty percent of those contacted ( N = 9613) proved willing to participate ( n = 4838). The participants were interviewed at home by trained interviewers and asked to complete a "drop-off" questionnaire after the interviewer left. The return rate for the questionnaire was 83.4% ( n = 4034). Because most measures used for the present research were collected by means of the drop-off questionnaire, we decided to restrict the analysis to the respondents who completed this questionnaire. Although this final sample still is very large ( n = 4034), it consists of less than half of the original sample, which may yield problems of generalizability. Therefore, to identify possible sample selections, we conducted a specific nonresponse analysis (Infas 1997 ). First, the main characteristics of the people who refused to participate entirely were analyzed. It was found that more people refused to participate because of disability and illness in the highest age group of 70 to 85 years than in the other groups. Also, women generally refused to participate more often than men did (53% vs. 47%) and East Germans were slightly more willing to participate than West Germans were (56% vs. 48%). Second, a comparison was made between the participants who did return the questionnaire after being interviewed (the final sample; n = 4034) and those who did not return the questionnaire ( n = 804). Results showed that this nonresponse group, compared with the final sample, contained slightly more women (50.4% vs. 48.8%) and somewhat more West Germans (71.4% vs. 66.1%). There were no differences regarding age. From these analyses it was concluded that, in interpreting the results, it should be kept in mind that the final sample contains a small overrepresentation of healthy people in the oldest age group (70 to 85 years), together with a small overrepresentation of East Germans and men. We return to the point of sample selection and generalizability in the Discussion. In Table 1 , an overview of the main demographic characteristics of the sample can be found.

The personal aging experience.

This concept was measured using an a priori set of 47 statements referring to both positive and negative aging experiences in such different life domains as health, social contacts, activities, personality, and so forth. All statements began with the phrase: "Aging means to me …" or ended with: "… has nothing to do with my age." (For an overview see Kohli and Dittmann-Kohli 1996 ). Examples of the statements are: "Aging means to me … being less vital and fit" and "Just how well I can take care of myself has nothing to do with my age." Respondents had to indicate whether each statement was "completely true," "mostly true," "mostly not true," or "completely not true." The statements were formulated by members of the research group and were based on the results of two pilot studies in which personal meanings of aging were investigated by means of qualitative methods (Kohli and Dittmann-Kohli 1996 ; see also Dittmann-Kohli 1995 ). The resulting initial set of 47 statements was explored using a number of data-reduction techniques. Analyses revealed three convincing clusters of statements regarding the aging experience (see Results).

Physical and material resources.

Two indicators were used to measure physical and material resources: subjective health and income. Subjective health was measured by responding to the question "How do you assess your health at this moment?" with "very good," "good," "moderate," "bad" or "very bad." Income was assessed using equivalence income (Motel 1998 ) translated into a 14-category classification system with the categories ranging from "less than 1000 German marks per month" (Category 1) to "more than 3400 German marks per month" (Category 14). Information about income was missing in 10.4% of the cases ( n = 418).

Social resources.

Three measures were used to assess the availability of social resources. The first measure was "having a spouse," which was dichotomized as "being married or living together with a spouse" versus "being widowed, divorced, or never married." The second measure was the number of children, which ranged from "no children" (score = 0) to "five or more children" (score = 5). For the latter score, the number of children was summed, as only 3.6% of the respondents were found to have five or more children, with 2 respondents having the maximum of 10 children. Twelve percent of the respondents had no children. Finally, a measure of loneliness was added because the other two more objective measures of social resources need not correspond with their subjectively experienced quality. That is, loneliness can reflect the subjectively experienced lack of important social resources and was therefore measured by an 11-item loneliness scale (DeJong-Gierveld and Kamphuis 1985 ). This scale has good psychometric properties and the internal consistency (Cronbach's α) for the present study was found to be .89.

Psychological resources.

We used two measures to assess the respondents' psychological resources: level of education and hope. Education was measured with the three categories: low, middle, and high. Hope was measured in terms of personal agency, using an eight-item hope scale (Snyder et al. 1991 ), to indicate "a cognitive set that is composed of a reciprocally derived sense of successful (a) agency (goal-directed determination) and (b) pathways (planning of ways to meet goals)" (p. 570). For the present study, the internal consistency (Cronbach's α) of this scale was found to be .87.

Subjective well-being.

Subjective well-being was measured by means of both a cognitive (life satisfaction) and two affective (positive and negative affect) components. These are widely used indicators of subjective well-being (Diener 1984 ; Diener, Suh, Lucas, and Smith 1999 ). Life satisfaction was measured with the five-item scale, Satisfaction with Life (Pavot and Diener 1993 ). This scale has good psychometric properties and the internal consistency coefficient for the present study was found to be .86. Positive and negative affect were measured using the Positive and Negative Affect Schedule, which consists of two scales of 10 items each (Watson, Clark, and Tellegen 1988 ). The internal consistency coefficients for the present study were found to be .87, and .82, respectively, for each scale.

Statistical Procedures

The first set of hypotheses was tested using factor analysis and analysis of internal consistency. The second and third sets of hypotheses were tested using multiple regression analyses. To check for a risk of collinearity in the multiple regression analyses, we examined the intercorrelations between the variables. Inspection of Table 2 shows none of the correlations to exceed .54 or −.43, which can be considered acceptable.

Although no hypotheses were formulated with regard to gender and region, both variables were controlled for in the regression analyses. In light of the fact that the sample was stratified by age, gender, and region, moreover, part of the analyses were performed on weighted cases. Where relevant, the use of weighted cases is indicated. A final remark concerns the testing of the causal mechanisms formulated in the second and third set of hypotheses. It should be noted that such testing essentially requires a longitudinal design. However, we believe that important initial insights can be gained from cross-sectional analyses, guided by clear theoretical assumptions. Nevertheless, the results should be interpreted with caution.

In the first set of hypotheses, we stated that the personal experience of aging would be characterized by multidimensionality and (weak) multidirectionality. These hypotheses were tested using different steps of factor analysis and data-reduction techniques. In the first step of the exploratory factor analysis, all 47 statements were analyzed by means of principal component analysis with Varimax rotation. This revealed eight factors with eigenvalues greater than 1.0 to explain a total of 49.2% of the variance when considered together. However, the largest part of the variance (35%) was explained by the first three factors (with eigenvalues of 9.2, 4.8, and 2.4 respectively). The remaining five factors each explained only 3% to 2% of the variance (and had eigenvalues between 1.7 and 1.1).

In light of these findings, we decided to carry out another factor analysis with a three-factor solution. This analysis revealed a first factor with 17 items, a second with 13 items, and a third with 10 items (only items with loadings greater than .40 were considered). The first factor contained negatively formulated items with very diverse content. The second factor, in contrast, contained a diversity of positive items. All of the items on the first and second factors also started with the phrase, "Aging means to me … ". The third factor contained a mixture of items with 6 of the 10 items ending with the alternative phrase: "… has nothing to do with my age." This finding led us to conclude that the items on the third factor were less convincing, and we decided to continue the analyses with only the items from the first and second factors with loadings of at least .40 (30 items).

As not only weak multidirectionality (positive and negative experiences), but also multidimensionality were expected to characterize the personal experience of aging, we decided to subject the 30 items selected on the basis of the previous analysis to another factor analysis. The result was five factors with eigenvalues of 7.1, 3.6, 1.9, 1.2, and 1.1, respectively, explaining 49.6% of the variance when considered together. The first factor contained seven items (with loadings >.40); all of the items referred to the aging experience of physical decline and problems of coping, with the exception of one item, which was then removed. The second factor also contained seven items (>.40) reflecting the positive aging experience of continued personal development, expansion, and new experiences. The third factor contained four items (>.40) referring to losses in the social domain. The fourth factor revealed three items (>.40) with the positive experiences of compensation ability, control, and self-knowledge. Finally, the fifth factor contained six varied items referring to alienation, negative personality characteristics, dissatisfaction, and curiosity about the future.

To determine whether each factor represented a meaningful and coherent dimension of the aging experience, to use as separate scales in the further analyses, we further analyzed each factor with respect to internal consistency. An internal consistency coefficient (Cronbach's α) of at least .70 and meaningful content were taken as the criteria for acceptance.

The results of this analysis revealed the following. The six items from the first factor showed an internal consistency coefficient (Cronbach's α) of .82. The seven items from the second factor showed an internal consistency coefficient of .81. The four items from the third factor revealed a Cronbach's alpha of .77 and the three items from the fourth factor and the six items from the fifth factor revealed coefficients of .69 and .65, respectively.

According to the criteria, the fourth and fifth factors were unacceptable. The internal consistency of the fourth factor could not be increased because this factor had only three items. It was therefore decided to remove the items. Similarly, deletion of one or two of the items from the fifth factor did not increase the internal consistency of this factor, so it was also decided to remove these items. This led to a final set of three factors.

Before performing further analyses, we decided to delete two more items from the first factor. Both of the items loaded considerably smaller than the other items on this factor, and one of the items was considered vague with regard to content (it focused on coping with life in general). The resulting factor or dimension could be labeled as aging experiences of physical decline . An additional item was similarly deleted from the second factor because it showed a somewhat weaker loading than the other items. This factor or dimension could be labeled as aging experiences of continuous growth . Inspection of the third factor showed no reason for change, so the four items loading on it were retained. The third factor or dimension could be labeled as aging experiences of social loss .

It was next observed that the first and third factors each contained four items, whereas the second factor contained six items. For purposes of comparison, we deemed it desirable to have the same number of items on each factor, and we therefore considered restriction of the second factor to four items. Reduction of the second factor to four items did not appear to damage the meaningfulness or internal consistency of the factor; only a slight change in the internal consistency of the items was observed after the omission of two items (from α = .81 to α = .78). In Table 3 , the final results of the factor analysis and the internal consistency of the items are summarized.

As can be seen, all of the items load high on the factor they belong to and low on the other two factors. The total amount of variance explained by the three factors adds to 60.5%. The internal consistency coefficients (Cronbach's α) for the three factors were found to be .79, .78, and .77, which can be considered satisfactory.

The conclusion is that the subjective experience of aging is both multidimensional and multidirectional, with the latter implying the coexistence of both negative and positive experiences (i.e., weak multidirectionality). The multidimensionality of the aging experience can be seen to pertain to the physical-, social-, and personal-development domains of life.

In the second set of hypotheses we stated, first, that age would have an influence on the personal experience of aging such that strong multidirectionality would not obtain: With increasing age, the experience of aging becomes less positive and more negative. The results regarding this hypothesis show the following. All three factors or dimensions of the aging experience are found to correlate significantly with age in the expected direction ( p < .01). Whereas the dimensions of physical decline and continuous growth produced age correlations of r = .31 and r = −.35, respectively, the dimension of social loss revealed an age correlation of r = .18. To check the linearity of these relationships, we compared the mean scores for the six age groups (40–46, 47–54, 55–61, 62–69, 70–76, and 77–85 years) on each dimension. A clear linear relationship with age was found for each of the three dimensions of the personal experience of aging (weighted cases). Both the negative dimensions (physical decline and social loss) show that the older one is, the more the aging experience is framed either in terms of physical decline, F (3895,5) = 83.35, p < .001, or in terms of social loss, F (3944,5) = 35.58, p < .001. The dimension of continuous growth shows the process of aging to be experienced as less of a process of continuous growth with increasing age, F (3846,5) = 124.01, p < .001.

In Table 4 , the results pertaining to the other hypotheses of the second set of hypotheses are shown. It was stated that individuals with higher levels of resources could be expected to be generally less negative and feel more positive about growing older than would individuals with lower levels of resources. Also, although actual age is expected to have an independent influence on the personal experience of aging, the influence of resources was expected to be greater. We performed separate regression analyses with the three dimensions of the personal experience of aging as the dependent variables. All three models are shown in Table 4 , each model containing two submodels. Each first submodel includes only age; each second submodel also includes the following resources: subjective health, income, having a spouse, number of children, loneliness, education, and hope. Also, gender and living region in Germany (West or East) were added to each second submodel to allow us to examine the possible influence of these variables.

The results in Table 4 again show age to significantly influence all three dimensions of the aging experience. Significant influences of the resources of subjective health, income, loneliness, and hope were also found for the three dimensions of the aging experience. We found that better subjective health, a higher income, less loneliness, and stronger hope contributed to the experience of less physical decline, more continuous growth, and less social loss. Two of the resources (i.e., having a spouse and education) differentially contributed to the experience of aging. People with a spouse experienced aging as less of a social loss than did people without a spouse. With respect to both the physical decline and the continuous growth dimensions of the aging experience, having a spouse surprisingly exerted no influence.

The resource of education also relates differentially to the three dimensions of the aging experience. A higher educational level relates to the experience of aging as less of a social loss, and more as an opportunity for continuous growth. The relation to physical decline was nonsignificant, however. A higher educational level does not, thus, seem to protect an individual from experiencing aging as physical decline. Finally, one of the resources considered here—number of children—did not influence any dimension of the aging experience, which is certainly unexpected and is considered in further detail in the Discussion.

Comparison of the standardized regression coefficients (β) for each second model shows only a few of the resources playing a stronger role in how people experience the aging process than actual age. The aging experience of physical decline appears to be better predicted by subjective health than by actual age. The aging experience of continuous growth appears to be better predicted by hope than by actual age. Additionally, the aging experience of social loss appears to be better predicted by loneliness and hope than by actual age. These findings lead us to conclude that age is a relatively strong and independent determinant of just how the process of aging is experienced. Only a few resources (or lack of them) appear to affect the aging experience more than actual age.

With respect to gender, it is remarkable that it does not relate to the experience of aging as physical decline but does relate to the experience of aging as both social loss and an opportunity for continuous growth. Men and women apparently do not differ with respect to the experience of aging as physical decline, whereas men tend to feel greater social loss as a result of aging than women, and women experience more continuous growth than men.

With respect to region of living, it is interesting to note that East Germans seem to experience the aging process as less of an opportunity for continuous growth than do West Germans, although they do not differ with respect to the experiences of physical decline and social loss. This finding is hard to interpret but, in light of the fact that the influences of income and health have been taken into consideration, it may simply indicate a more general lack of opportunities for continuous growth in East Germany relative to West Germany.

The third set of hypotheses in the present study concerned the influence of the different dimensions of the personal experience of aging on measures of subjective well-being (i.e., life satisfaction, positive affect, and negative affect). Note here that, although the rationale for the relationship between (different dimensions of) the aging experience and indicators of subjective well-being is based on the hypothesized intermediate mechanism of "making the right decisions" (linking positive cognitions to adaptive outcomes and negative cognitions to maladaptive outcomes), this intermediate step could not be measured with the available data. Nevertheless, we deemed it acceptable to interpret the empirically found relationships—if supported—as such.

The results of separate regression analyses with the three measures of subjective well-being as the dependent variables are presented in Table 5 . Again, each model consists of two submodels. Each first submodel contains age, resources, gender, and region as independent variables. Each second submodel also includes the three dimensions of the personal aging experience.

Inspection of Table 5 first reveals the often-found positive relationship between age and life satisfaction and the fact that age is negatively related to both positive and negative affect. Next, we found the three dimensions of the personal experience of aging significantly related to at least two of the three indicators of subjective well-being. The experience of aging as physical decline relates to both positive and negative affect (as expected) but not to life satisfaction (which was unexpected). The experience of aging as continuous growth positively relates to life satisfaction and positive affect (as expected) but also to stronger feelings of negative affect (which was unexpected). This deviant coefficient is hard to interpret, a point to which we return in the Discussion. Finally, the experience of aging as social loss relates in the expected direction to all three indicators of subjective well-being. Feelings of social loss as a result of aging lead to decreased life satisfaction, decreased positive affect, and increased feelings of negative affect.

In general, it may be concluded that the third set of hypotheses is largely supported by the data. The way in which people experience their own aging process independently affects how they feel in terms of both life satisfaction and positive or negative affect. Comparison of the standardized coefficients (β) for the three dimensions of the personal aging experience together with the increase in the amount of explained variance, however, shows the impact of various aspects of the experience on life satisfaction to be very small, the impact on positive affect to be particularly due to the experience of continuous growth, and the impact on negative affect to be mainly a matter of physical decline and social loss.

In this study, we investigated how people in the second half of life experience their personal aging process, the factors associated with the way in which they perceive their aging, and, finally, how their perceptions of the personal aging process relate to indicators of subjective well-being. A number of hypotheses were formulated and tested in a sample of 4034 Germans aged 40 to 85.

The findings primarily showed the personal experience of aging to be a multidimensional phenomenon. Three different dimensions of aging experiences were found. The first dimension relates to physical decline, such as the loss of vitality and health. The second dimension relates to continuous growth and personal development. The third dimension relates to losses in the social domain, such as no longer being needed by others or decreased respect from others. The three dimensions of the aging experience found here are largely in line with the findings of a study by Keller and colleagues 1989 , who identified two additional dimensions: Aging as a natural and gradual process with little or no remarkable features and aging as a period of life evaluation, philosophical reflection, and increased wisdom. Although our data initially also revealed more than three dimensions (see Results), only three dimensions could be interpreted unambiguously while at the same being internally consistent scales. The fact that Keller and colleagues 1989 reported on more than three dimensions may lie in their use of open-ended questions to tap the subjective experience of aging. Such a qualitative procedure (but only in 32 adults aged 50 to 80) may yield results that are hard to replicate in a large quantitative and statistically controlled study. Conversely, the set of statements used in our study may have been insufficient in content and/or number to identify other statistically significant dimensions. Further research should take these points into consideration.

A second finding concerns the multidirectionality of the aging experience, which, on the one hand, is reflected by the fact that both positive (growth) and negative (loss and decline) experiences characterize the personal experience of aging (i.e., weak multidirectionality). On the other hand, we found, as expected, that strong multidirectionality of aging experiences does not obtain: With increasing age, the aging experience is increasingly framed in terms of physical decline or social loss and less in terms of continuous growth.

A third major finding in the present study is that, next to age, a substantial number of the resources were significantly related to each of the three dimensions of the aging experience. Adults with better subjective health, a higher income, less loneliness, a higher educational level, and stronger hope experience the process of aging less in terms of physical decline and social losses and more in terms of continuous growth. Only two of the resources examined in our research did not relate to the experience of aging in the manner expected. People with fewer children were found to hold a more negative view of aging than were people with more children in a study by Connidis 1989 , whereas our data showed no differences. One explanation for this may lie in the fact that our study covered the range of 40 to 85 years, whereas the study by Connidis involved only adults over the age of 65 years. Younger participants are possibly less aware of how dependent they can become on their children when they age. Nevertheless, it may also be the case that it is not so much the number of children that is important for feeling more or less worried about one's own aging process, but having any children (versus having no children). Moreover, having children as a continuous variable may contain the risk of curvilinearity. To check these possibilities, we also executed all regression analyses with having children as a dichotomous variable. This, however, did not yield other results. Another possible explanation may still be that it is not so much the number of children that is important, but the quality of the relationship with one's children. As we also considered the perceived quality of one's social relations (including children) indirectly through the level of loneliness, the possible influence of number of children may have been masked by the significant relationship of loneliness to all three dimensions of the aging experience.

The other resource not relating to the experience of aging in the manner expected was having a spouse. In the study by Connidis 1989 , the people holding a negative view of aging were more likely to have never been married; in our study, the people less likely to experience aging as a social loss were married. However, having (or not having) a spouse did not relate to experiencing the process of aging in terms of physical decline or continuous growth. It seems that the implications of having (or not having) a spouse for one's experience of aging primarily refer to the social domain. This finding can be interpreted as a differentiation of the finding of Connidis 1989 and shows the importance of investigating the aging experience not only in positive or negative terms, but also in different dimensions.

In addition to several resources, actual age was found to influence the three dimensions of the aging experience rather strongly, which was not quite as expected. The influence of age on the different dimensions of the aging experience appeared to be sometimes equal but often stronger than most of the resources examined. The higher the age, the more inclined the people were to frame the aging process in terms of physical decline and social loss and less in terms of continuous growth, regardless of most of their resources. Only three resources appeared to have a stronger impact on the dimensions of the aging experience than actual age. First, subjective health influenced the aging experience of physical decline more than actual age did. This means that actually feeling less healthy and not so much being older leads one to experience the process of aging in terms of physical decline. Also, the experience of aging in terms of continuous growth appears to depend more on a higher level of hope than on being younger. Finally, the experience of aging in terms of social loss seems to be triggered by loneliness and a low level of hope rather than by simply being older. The findings regarding these three resources partly support our hypothesis that the impact of resources on the personal aging experience would be stronger than actual age. Besides, it shows that evaluation of these three resources in particular is associated with the personal process of aging. Here it should be noted also that there may be a difference between actual resources such as income, spouse, and education, and perceived resources such as subjective health, loneliness, and hope, when relating them to the different dimensions of the aging experience. Perceived resources may have a different relationship to the three dimensions of aging experiences than do actual resources, because both perceived resources and aging experiences are measured as subjective evaluations (i.e., perception), whereas actual resources are measured as objective facts. What remains to be seen, however, is whether such evaluations are based on real experiences or on misconceptions about aging. For instance, people can be lonely because they lack companionship and not because of their age. Still, they may be inclined to attribute this experience to the aging process.

Also the finding that age still exerts a relatively strong independent influence on the personal experience of aging after all resources (including health, loneliness, and hope) were controlled for is intriguing. To examine whether stepwise multiple regression analyses would yield more insight into the separate impact of age and the different resources, we also executed all regression models using stepwise methods. This, however, did not change the results. The relatively strong influence of age may also suggest that, although they were asked about their personal experience of aging, people may still be inclined to intermingle personal experiences of aging with normative (i.e., more negative and less positive) expectations. Normative expectations are associated with actual age. Therefore, even when the influence of other important factors (i.e., resources) has been controlled for, actual age may still have a relatively strong impact on the personal experience of aging through internalized normative expectations with regard to aging. These findings are intriguing and in need of further research, particularly when it is realized that misconceptions about aging may lead to unnecessary worries about the process and may ultimately have a negative impact on the quality of life (see also Neikrug 1998 ).

Our results regarding the relations between the personal experience of aging and measures of subjective well-being (i.e., life satisfaction, positive affect, negative affect) also point to the negative effect of misconceptions about aging on quality of life. All three measures of subjective well-being were found to be substantially influenced by at least two of the three dimensions of the aging experience. Only two effects deviated from the expected pattern of results. First, experiences of physical decline do not appear to influence life satisfaction although they do relate to both positive and negative affect. This finding may be due to the fact that life satisfaction was measured in terms of overall satisfaction with one's life. Moreover, experiences of physical decline may be seen as trivial and generally accepted as a normal part of the aging process. Positive and negative affect, however, are more state measures and thus, perhaps, more sensitive to feelings of physical decline. Nevertheless, it remains intriguing that experiences of social loss and continuous growth, which indeed relate significantly to life satisfaction, apparently are not considered trivial or simply part of the aging process. The other unexpected finding was the positive relationship between the experience of aging as continuous growth and feelings of negative affect. This may be due in part to the positive correlation between positive and negative affect ( r = .14, see Table 2 ). Another explanation, however, is that people who experience aging in terms of continuous growth are open to new opportunities, which may sometimes yield positive experiences and sometimes negative ones. Further research is needed to elucidate these findings.

Three final points for discussion and future research should be mentioned. The first concerns the relatively large nonresponse this study encountered and its consequences for interpreting the results. Although such a rate of nonresponse is common in large-scale population surveys, it urges researchers to be cautious when generalizing the results to the German population. On the other hand it may be argued that, because the main sample biases could be identified (see Methods section), it is known at what points the generalizability is limited. Moreover, as this article also aimed at elaborating theoretical issues and model building, the study is deemed interesting for that purpose as well.

The second point concerns causality. The direction of causality for a number of the relations observed in the present, cross-sectional, research can only be determined on the basis of longitudinal data. Nevertheless, as a first attempt to shed some light on the personal experience of aging and the factors particularly relevant to it, a cross-sectional design can provide some useful insights, particularly when the analyses of the cross-sectional data are guided by specific theoretical considerations. Moreover, some useful insights for further (longitudinal) examination may be gained in such a manner.

The last point for consideration in future research is whether other resources or particular personality characteristics such as optimism may play a role in people's cognitions about their own aging process. The substantial amount of variance left unexplained in the present analyses suggest such a possibility.

It may be concluded that the personal experience of aging encompasses more than just a particular age identity. The personal experience of aging has a number of different dimensions and includes both negative and positive experiences. Furthermore, the personal experience of aging seems to play a role in just how happy people may feel in terms of the degrees of both positive and negative affect. The present findings may contribute to our knowledge of the personal experience of aging and may help identify those people at risk for developing a particular negative view of the process of aging. Such information can also be used to develop interventions aimed at a more positive aging experience and greater subjective well-being in later life.

Descriptive Characteristics of the Sample ( n = 4034)

Mean age = 60.1 years ( SD = 12.2).

Pearson Correlations Between all Variables (Weighted Cases)

* p < .05. * *p < .01.

Items, Factor Loadings, Explained Variance, and Internal Consistency

Notes : Respondents had to indicate the degree to which they considered each statement to be: 1 = completely true , 2 = mostly true , 3 = mostly not true , 4 = completely not true . Factor loadings are based on principal component analysis with Varimax rotation. Factor loadings in italics indicate which items are the high factor loadings for each factor. PD = physical decline; CG = continuous growth; SL = social loss.

Regression Analyses for the Three Dimensions of the Aging Experience

Note : Only standardized coefficients are shown.

p < .05. ** p < .01. *** p < .001.

Regression Analyses for Life Satisfaction, Positive Affect, and Negative Affect

This research was conducted within the context of the "German Aging Survey" (Deutscher Alters-Survey), which is a collaborative project between the Department of Sociology (Martin Kohli), Free University of Berlin, Germany, and the Department of Psychogerontology (Freya Dittmann-Kohli), University of Nijmegen, The Netherlands. The study was financed by the German Federal Ministry of Family Affairs, Senior Citizens, Women, and Youth, Grant 314-1720-317. Sample selection and data collection were carried out by the Institute for Social Research, Bonn, Germany.

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Aging is inevitable, so why not do it joyfully? Here’s how

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This post is part of TED’s “How to Be a Better Human” series, each of which contains a piece of helpful advice from people in the TED community;  browse through  all the posts here .

It was recently my birthday. It wasn’t a “big” birthday — one of those round-numbered ones that feels like a milestone — but nevertheless it got me thinking about aging.

When I was a kid, growing older felt like an achievement. Each year that passed marked one step closer to adulthood, which for me meant independence and freedom. I remember going to the city with my dad to see plays or go to the Met and seeing a group of women having lunch in a café. It seemed glamorous and exciting to be an adult. I couldn’t wait.

Likewise, I never quite understood the popular antipathy toward old age. At Spencer’s, a novelty store at the Galleria Mall in White Plains where my friends and I would find gag gifts, I was always perplexed by the section of “Over the Hill” merchandise. I mean, my grandparents didn’t listen to my music or play Nintendo with me, but they were cool in their own way — not crusty and out of touch like the caricatures suggested. The geezer jokes and “lying about your age” punchlines that adorned the mugs and t-shirts there seemed to come from another world, one that didn’t make sense to me.

In my 20s and 30s, friends would casually toss around the phrase “We’re so old!” I rolled my eyes. We were so young, I felt, and why should we waste that youth focused on what was already behind us? After all, right at that moment we were the youngest we would ever be.

My 20s were miles better than my teens — more expansive, less cloistered —  and my 30s better than my 20s. I became more confident in my 30s, I got into therapy and dealt with years of childhood trauma, I learned to communicate my needs and be more mindful of the needs of others. I wouldn’t trade the growth of these past decades for fewer lines on my face or grey hairs on my head.

Author Heather Havrilesky wrote: “Growing old gracefully really means either disappearing or sticking around but always lying straight to people’s faces about the strength of your feelings and desires.”

Now that I’m in my 40s, though, aging isn’t some future concept. Just being alive means growing older, so yes, we’ve all been aging since we were born. But at a certain point, the notion of what life will be like in a couple of decades starts to feel more real, and then I start to reflect more on what my current choices mean for that future me.

I look back and wonder what my work-hard-play-hard 20s mean for me now. Could I have had a healthier body today if I had been kinder to it when I was younger? And could being gentler now give me more joy and freedom in the future?

The dominant discourse on aging, especially when it comes to women, revolves around “aging gracefully.” This generally involves looking at least three to five years younger than you actually are, while not appearing to do anything to get that way. It also means “acting your age,” by wearing age-appropriate clothes (mini skirts have an expiration date, apparently), having age-appropriate hair and doing age-appropriate activities — but maybe doing one or two surprisingly youthful things (surfing, maybe, or tap dancing) that don’t seem like you’re trying too hard yet let people know you’re still in the game.

As author Heather Havrilesky writes in her biting essay on the topic , “I think about how growing old gracefully really means either disappearing or sticking around but always lying straight to people’s faces about the strength of your feelings and desires.”

The only way to age and be deemed acceptable is to have lucky genes or to conceal your battles against time underneath a practiced smile.

“Aging gracefully” entails walking a tightrope between a youth-obsessed society, which tells us that our value declines as we age, and a culture that says nothing is as uncool as desperation, the fervent desire for something we can’t have. Marketers stoke our desire for youthfulness as the ticket to remaining relevant, then shame us when our efforts to preserve that youth go awry.

So the person who ages without thought to their appearance is written off as “having given up,” and the one whose face remains 35 forever thanks to the surgeon’s knife is considered a joke, and the only way to be deemed acceptable is to have lucky genes or to conceal your battles against time underneath a practiced smile. It all sounds exhausting, doesn’t it?

And so I’ve been thinking about how we move beyond this damaging — and frankly misogynistic — frame. What if instead of seeing aging as something to defeat and conquer, we were to embrace what gets better with age, and work to amplify these joys while mitigating the losses of youth? I’m not suggesting we paper over the very real challenges, both physical and mental, that come with aging. But can we view these challenges without judgment or shame and instead look for joyful ways to navigate them?

I delved into the research on aging, and here are 8 insights I’ve found that can help us think about joyful ways to feel well as we grow older.

1. Seek out awe 

In a study of older adults, researchers found that taking an “awe walk,” a walk specifically focused on attending to vast or inspiring things in the environment, increased joy and prosocial emotions (feelings like generosity and kindness) more than simply taking a stroll in nature. Interestingly, they also found that “smile intensity,” a measure of how much the participants smiled, increased over the eight-week duration of the study. These walks were only 15 minutes long, once a week, and are low impact, so this is an easy way to create more joy in daily life as we age.

Practiced joyspotters well know the power of attending to joyful stimuli in the environment to boost mood. This study suggests that tuning our attention specifically to things that invoke wonder and awe can have measurable benefits, especially for older adults.

2. Get a culture fix 

A 1996 study of more than 12,000 people Sweden found that attending cultural events correlated with increased survival, while people who rarely attended cultural events had a higher risk of mortality. Since then, a raft of studies (a good summary of them here ) has affirmed that people who participate in social activities such as attending church, going to the movies, playing cards or bingo, or going to restaurants or sporting events is linked with decreased mortality among older adults. One reason may be that these activities increase social connection, deepen relationships, and reinforce feelings of belonging, which are positively associated with well-being. Cultural activities also help keep the mind sharp. While the pandemic has made this one challenging, as things start to open up again, getting a culture fix can be an easy way to age joyfully.

Enriching your environment with color, art, plants and other sensorially stimulating elements may be a worthwhile investment not just for protecting your mind as you age, but also your joy.

3. Stimulate your senses

One of the most talked-about parts of my TED Talk is when I describe my experience spending a night at the wildly colorful Reversible Destiny Lofts , an apartment building designed by the artist Arakawa and the poet Madeline Gins, who believed it could reverse aging.

The idea that an apartment could reverse aging sounds farfetched, but it becomes more grounded when we look at the theory behind it. Arakawa and Gins believed that just as our muscles atrophy if we don’t exercise them, our cognitive capacity diminishes if we don’t stimulate our senses. They looked at our beige, dull interiors and imagined that these spaces would make our minds wither. And as it turns out, some early research in animals ( see also ) suggests there might be something to this. When mice are placed in “enriched environments” with lots of sensorial stimuli and opportunities for physical movement, it mitigates neurological changes associated with Alzheimer’s and dementia. While there is some evidence to suggest that this might apply to humans as well, the mechanisms behind this phenomenon are not yet well understood.

That said, we do know that the acuity of our senses declines with age. The lenses of our eyes thicken and tinge more yellow, allowing less light into the eye. Our sense of smell, taste and hearing also become less sharp. So, while you don’t have to recreate Arakawa and Gins’s quirky apartments, enriching your environment with color, art, plants and other sensorially stimulating elements may be a worthwhile investment not just for protecting your mind as you age, but also your joy.

4. Buy yourself flowers 

As if you needed an excuse for this one, but just in case, here you go. A study of older adults found that memory and mood improved when people were given a gift of flowers, which wasn’t the case when they were given another kind of gift.

Why would flowers have this effect? One reason may link to research on the attention restoration effect, which shows that the passive stimulation we find in looking at greenery helps to restore our ability to concentrate. Perhaps improved attention also results in improved memory. Another possibility, which is pure speculation at this point, relates to the evolutionary rationale for our interest in flowers. Because flowers eventually become fruit, it would have made sense for our ancestors to take an interest in them and remember their location. Monitoring the locations of flowers would allow them to save time and energy when it came to finding fruiting plants later, and potentially reach the fruit before other hungry animals. I have to stress that there’s no evidence I’m aware of to support this explanation, but it’s an intriguing possibility.

Taking it a step further, research has also shown that gardening can have mental and physical health benefits for older adults. So whether you buy your flowers or grow them, know that you’re taking a joyful step toward greater well-being in later life.

There’s something joyful about a mini time warp — maybe it’s revisiting a vacation spot you once loved or maybe it’s a getaway with friends where you banish talk of present-day concerns.

5. Try a time warp 

In 1981, Harvard psychologist Ellen Langer ran an experiment with a group of men in their 70s that has come to be known as “the counterclockwise study.” For five days, they lived inside a monastery that had been designed to look just like it was 1959. There were vintage radios and black-and-white TVs instead of cassette players and VHS. The books that lined the shelves were ones that were popular at the time. The magazines, TV shows, clothes and music were all throwbacks to that exact period.

But these men weren’t just living in a time warp. They also had to participate. They were treated like they were in their 50s, rather than their 70s. They had to carry their own bags. They discussed the news and sports of 22 years earlier in the present tense. And to preserve the illusion, there were no mirrors and no photos, except of their younger selves.

At the end of five days, the men stood taller, had greater manual dexterity, and even better vision. Independent judges said they looked younger. A touch football game broke out among the group (some of whom had previously walked with a cane) as they waited for the bus home. Langer was hesitant to publish her findings, concerned that the unusual method and small sample size might be hard for the academic community to accept. But in 2010, a BBC show recreated the experiment with aging celebrities to similar effect. Langer’s subsequent research has led her to conclude that we can prime our minds to feel younger, which in turn can make our bodies follow suit.

While it might be difficult to recreate Langer’s study in our own lives, I think there’s something joyful about a mini time warp. Maybe it’s revisiting a vacation spot you once loved, and steeping yourself in memories from an earlier time. Maybe it’s a getaway with friends where you banish all talk of present-day concerns. Maybe it’s finding a book or a stack of old magazines from back then and reading them while listening to throwback tunes.

It’s also worth noting that a control group from the counterclockwise study who simply reminisced about their youth, without using the present tense, did not experience the same dramatic results — so these “mini time warps” may be more for fun than for tangible benefit. But even if you don’t turn back the clock, checking back in with your younger self can be a way to rediscover parts of yourself that you may have lost touch with and bring them with you as you age.

6. Maximize mobility 

Exercise is often touted as a way to stay healthy and vibrant at any age , but one finding that makes it particularly relevant as we get older is that movement has been shown in studies to increase the size of the hippocampus, a part of the brain that plays a vital role in learning and memory. This is important because the hippocampus shrinks as we age, which can lead to memory deficits and increased risk of dementia. In one study of older adults, exercise increased hippocampus size by 2 percent , which is equivalent to reversing one to two years of age-related decline.

In addition to its cognitive effects, movement itself can be a source of joy. The ability to swim, hike, dance and play can be conduits to joy well into our older years. When I struggle to get motivated to exercise , I often think about my future self and how investing in my mobility now can help preserve range of motion and minimize repetitive stress injuries later. Simply put: you have one body, and it has to last your whole life. The more you do now to care for it, the more freedom you’ll have to do the things you love late in life.

As we age, we have a choice: We can either cling to the world as we shaped it and refuse to engage in the new world that kids are creating, or we can adapt to their world and remain curious, active participants.

7. Refeather your nest

Once you start looking at negative tropes around aging, you start seeing more and more of them. Take the phrase “empty nest,” which carries strong connotations of loss and deprivation. Though I’m at the stage where my nest suddenly just became quite full, I love the idea of reframing the “empty nest” into something more joyful.

One of my readers, Lee-Anne Ragan, offers up as a joyful process in the wake of children going off to start their own independent lives. She points out that the idea of an empty nest suggests that there’s nothing left, while refeathering takes a more ecological lens, imagining a kind of regeneration that happens as the home, and the family, transforms into something new. A refeathered nest is a place of possibility, creativity and delight.

8. Stay up on tech

While technology is often blamed for feelings of isolation, some studies show that for older adults, being technologically facile can offer a boost to well-being. One reason is that internet use may serve a predictor of social connection more broadly, and social connection is one of the most important contributors toward mental health and well-being throughout life, but especially in old age. Other studies suggest that when older adults lack the skills to be able to use technology effectively, it leads to a greater sense of disconnection and disempowerment  and that offering training to older adults on technology can promote cognitive function, interpersonal connection and a sense of control and independence.

I’ve often been tempted, when a radically new app or device comes out, to say “That’s for the kids,” and ignore it. With free time so scarce, exploring new tech feels less appealing than digging into one of the books piled up on my nightstand. And anyway, unplugging is supposed to be good for us, right? But technology shapes the world we live in, and those technologies that seem new and fringy in the moment often end up in the mainstream, influencing the ways we communicate, work and access even basic services.

I remember trying to teach my grandmother how to use email. She was someone who never wanted to bother anyone, and I thought that email’s asynchronous communication would be good for her. Instead of calling, she could just send a note and know that she wasn’t interrupting anyone. She tried, but she struggled to learn it. She had stopped caring about technology long before that, and the leap to figure out how to use a computer was too great. Small choices not to engage with a new technology don’t matter much in the moment, but once you get a few steps down the road to disconnection, it can feel intimidating to try to plug back in.

Staying engaged with new technologies doesn’t have to be a burden. It might simply mean saying yes when a niece or nephew invites you play Minecraft or opening a TikTok account just to check it out. You don’t have to master every new app or tool, but being comfortable with new developments can help you ensure you don’t end up feeling helpless or blindsided when the tech you rely on every day changes.

I think a lot about something psychologist Alison Gopnik said when I interviewed her for the Joy Makeover a couple of years ago. She said that each new generation breaks paradigms and overturns old ways of doing things as a matter of course. This isn’t gratuitous — it’s how we move forward as a society. Each generation of kids will remake the world, and from this we’ll gain all kinds of new discoveries. So as we age, we have a choice: we can either cling to the world as we shaped it and refuse to engage in the new world our kids’ and grandkids’ generations are creating, or we can adapt to their world and remain curious, active participants in it.

This to me is at the heart of aging joyfully. Our goal shouldn’t be to cling to youth as we get older, but to keep our joy alive by tending our inner child throughout our days while also nurturing our connection to the changing world. In doing so, we balance wisdom with wonder, confidence with curiosity and depth with delight.

This post was first published on Ingrid Fetell Lee’s site, The Aesthetics of Joy .

Watch her TED Talk now:

About the author

Ingrid Fetell Lee is the founder of the blog The Aesthetics of Joy and was formerly design director at the global innovation firm IDEO.

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Home > Books > Gerontology

Ageing Process and Physiological Changes

Reviewed: 06 March 2018 Published: 04 July 2018

DOI: 10.5772/intechopen.76249

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Ageing is a natural process. Everyone must undergo this phase of life at his or her own time and pace. In the broader sense, ageing reflects all the changes taking place over the course of life. These changes start from birth—one grows, develops and attains maturity. To the young, ageing is exciting. Middle age is the time when people notice the age-related changes like greying of hair, wrinkled skin and a fair amount of physical decline. Even the healthiest, aesthetically fit cannot escape these changes. Slow and steady physical impairment and functional disability are noticed resulting in increased dependency in the period of old age. According to World Health Organization, ageing is a course of biological reality which starts at conception and ends with death. It has its own dynamics, much beyond human control. However, this process of ageing is also subject to the constructions by which each society makes sense of old age. In most of the developed countries, the age of 60 is considered equivalent to retirement age and it is said to be the beginning of old age. In this chapter, you understand the details of ageing processes and associated physiological changes.

• physiological changes
• elderly health
• sensory changes

Author Information

Shilpa amarya *.

• Lady Irwin College, University of Delhi, New Delhi, India

Kalyani Singh

Manisha sabharwal.

*Address all correspondence to: [email protected]

1. Introduction

The term ‘Elderly’ is applied to those individuals belonging to age 60 years and above, who represent the fastest growing segment of populations throughout the world. The percentage of elderly in developing countries tends to be small, although numbers are often large. In the year 1990, there were more than 280 million people belonging to the age 60 years or over in developing regions of the world, and 58% of the world’s elderly were living in less-developed regions [ 1 ].

According to World Population Prospects (1950–2050), the proportion of elderly in developing countries is rising more rapidly, in comparison with developed ones [ 2 ]. The report published by the US Department of Health and Human Services shows that more developed nations have had decades to adjust to this change in age structure ( Figures 1 and 2 ). As we see in Figure 1 , it has taken more than a century for France’s population aged 65 or older to rise from 7 to 14%, whereas many developing countries are growing rapidly in number and percentage of older individuals [ 2 ].

Speed of population ageing in developed countries. Source: U.S. Census Bureau [ 3 ]; Kinsella & Gist [ 4 ].

Speed of population ageing in developing countries. Source: U.S. Census Bureau [ 3 ]; Kinsella & Gist [ 4 ].

It is expected that by the year 2020, 70% of the world’s elderly population will be in developing countries, with the absolute number exceeding 470 million which is double the number of the developed world [ 5 ]. The main factor responsible for this changing pattern of population ageing includes a rapid decline in both fertility and premature mortality [ 6 ]. Decline in fertility is particularly apparent in some developing countries like China, Cuba and Uruguay, although the fertility level in other developing countries such as Kenya, Zaire and Bangladesh remains high [ 7 ].

2. Ageing process and physiological changes

2.1. changes in nervous system.

Ageing is associated with many neurological disorders, as the capacity of the brain to transmit signals and communicate reduces. Loss of brain function is the biggest fear among elderly which includes loss of the very persona from dementia (usually Alzheimer’s disease). Multiple other neurodegenerative conditions like Parkinson’s disease or the sudden devastation of a stroke are also increasingly common with age [ 8 ].

Alzheimer’s and Parkinson’s diseases are the progressive neurodegenerative diseases associated with ageing [ 9 ]. Alzheimer’s is characterised by progressive cognitive deterioration along with a change in behaviour and a decline in activities of daily living. Alzheimer’s is the most common type of pre-senile and senile dementia. This disease causes nerve cell death and tissue loss throughout the brain, affecting nearly all its functions. The cortex in the brain shrivels up and this damages the areas involved in thinking, planning and remembering. The shrinkage in a nerve cell is especially severe in the hippocampus (an area of the cortex that plays a key role in the formation of new memories) as well as the ventricles (fluid-filled spaces within the brain) also grow larger. Alzheimer’s disease causes an overall misbalance among the elderly by causing memory loss, changes in personality and behaviour-like depression, apathy, social withdrawal, mood swings, distrust in others, irritability and aggressiveness [ 10 , 11 ].

Nearly, 33 million Indians have neurological disorders, and these occur twice as often in rural areas [ 12 ]. According to the World Health Organisation (WHO) [ 13 ], nearly 5% of men and 6% of women aged 60 years or above are affected with Alzheimer’s-type dementia worldwide. In India, the total prevalence of dementia per 1000 elderly is 33.6%, of which vascular dementia constitutes approximately 39% and Alzheimer’s disease constitutes approximately 54% [ 14 ].

Stroke is another common cause of mortality worldwide [ 13 ]. However, in India, the prevalence rate of stroke among elderly is reported to be very low compared to Western countries [ 15 , 16 , 17 ].

2.2. Cognition

A mild decline in the overall accuracy is observed with the beginning of the 60s that progresses slowly, but sustained attention is good in healthy older adults. Cognitive function declines and impairments are frequently observed among the elderly. Normally, these changes occur as outcomes of distal or proximal life events, where distal events are early life experiences such as cultural, physical and social conditions that influence functioning and cognitive development [ 17 ].

Cognition decline results from proximal factors (multiple serial cognitive processes) including processing speed, size of working memory, inhibition of extraneous environmental stimuli and sensory losses. This is a threat to the quality of life of those affected individuals and their caregivers [ 18 ].

Impaired cognition among elderly is associated with an increased risk of injuries to self or others, the decline in functional activities of daily living and an increased risk of mortality [ 19 , 20 , 21 ]. Mild cognitive impairment is increasingly being recognised as a transitional state between normal ageing and dementia [ 22 , 23 ].

2.3. Memory, learning and intelligence

According to various studies [ 24 , 25 , 26 ], the effect of normal ageing on memory may result from the subtly changing environment within the brain. The brain’s volume peaks at the early 20s and it declines gradually for rest of the life. In the 40s, the cortex starts to shrink and people start noticing the subtle changes in their ability to remember or to do more than one task at a time. Other key areas like neurons shrink or undergo atrophy and a large reduction in the extensiveness of connections among neurons (dendritic loss) is also noticed. During normal ageing, blood flow in the brain decreases and gets less efficient at recruiting different areas into operations. The whole group of changes taking place in the brain with ageing decreases the efficiency of cell-to-cell communication, which declines the ability to retrieve and learn [ 27 ]. It also affects the intelligence, especially fluid intelligence (problem-solving with a novel material requiring complex relations) declines rapidly after adolescence. Perceptual motor skills (timed tasks) decline with age [ 28 ].

2.4. Special senses

2.4.1. vision.

Ageing includes a decline in accommodation (presbyopia), glare tolerance, adaptation, low-contrast activity, attentional visual fields and colour discrimination. Changes occur in central processing and in the components of the eye. These numerous changes affect reading, balancing and driving [ 29 ].

2.4.2. Hearing

Ageing causes conductive and sensory hearing losses (presbycusis); the loss is primarily high tones, making consonants in speech difficult to discriminate [ 30 ].

2.4.3. Taste acuity

Losing sense of taste is a common problem among adults [ 31 ]. Taste acuity does not diminish but salt detection declines. Perception of sweet is unchanged and bitter is exaggerated. The salivary glands get affected, and the volume and quality of saliva diminish. All changes combine to make eating less interesting [ 32 ]. Studies show that the physiological decline in the density of the taste acuity and papillae results in a decline of gustatory function [ 33 ]. In fact, studies done on taste dysfunction show that ageing-associated changes in the density of taste acuity may affect taste function differently in different regions of the tongue [ 34 ]. Taste perception declines during the normal ageing process. A study done on the healthy elderly shows that after about 70 years of age, taste threshold begins to increase resulting in dysgeusia [ 34 ]. Chewing problems associated with loss of teeth and use of dentures also interfere with taste sensation and cause reduction in saliva production [ 32 ].

2.4.4. Smell

As we get older, our olfactory function declines [ 35 ]. Hyposmia (reduced ability to smell and to detect odours) is also observed with normal ageing [ 36 ]. The sense of smell reduces with an increase in age, and this affects the ability to discriminate between smells. A decreased sense of smell can lead to significant impairment of the quality of life, including taste disturbance and loss of pleasure from eating with resulting changes in weight and digestion [ 36 ].

It has been reported that more than 75% of people over the age of 80 years have evidence of major olfactory impairment. Many long-term studies show the evidence of a decline in olfaction considerably after the seventh decade [ 37 ]. Another study found that 62.5% of 80–97-year-olds had olfactory impairments [ 38 ]. However, it is widely accepted that taste disorders are far less prevalent than olfactory losses with age [ 38 ]. Ageing also causes atrophy of olfactory bulb neurons. Central processing is altered, resulting in a decreased perception and less interest in food [ 39 ].

2.4.5. Touch

As we age, our sense of touch often declines due to skin changes and reduced blood circulation to touch receptors or to the brain and spinal cord. Minor dietary deficiencies such as the deficiency of thiamine may also be a cause of changes [ 40 ]. The sense of touch also includes awareness of vibrations and pain. The skin, muscles, tendons, joints and internal organs have receptors that detect touch, temperature or pain [ 41 ].

A decline in the sense of touch affects simple motor skills, hand grip strength and balance. Studies have shown that muscle spindle (sensory receptors within the muscle that primarily detects changes in the length of this muscle) and mechanoreceptor (a sense organ or a cell that responds to mechanical stimuli such as touch or sound) functions decline with ageing, further interfering with balance [ 42 ].

3. Changes in musculoskeletal system

Normal ageing is characterised by a decrease in bone and muscle mass and an increase in adiposity [ 43 , 44 ]. A decline in muscle mass and a reduction in muscle strength lead to risk of fractures, frailty, reduction in the quality of life and loss of independence [ 45 ]. These changes in musculoskeletal system reflect the ageing process as well as consequences of a reduced physical activity. The muscle wasting in frail older persons is termed ‘sarcopaenia’. This disorder leads to a higher incidence of falls and fractures and a functional decline. Functional sarcopaenia or age-related musculoskeletal changes affect 7% of elderly above the age of 70 years, and the rate of deterioration increases with time, affecting over 20% of the elderly by the age of 80 [ 46 ]. Strength declines at 1.5% per year, and this accelerates to as much as 3% per year after 60 years of age [ 47 ]. These rates were considered high in sedentary individuals and twice as high in men as compared with those in women [ 48 ]. However, studies show that on an average, men have larger amounts of muscle mass and a shorter survival than women. This makes sarcopaenia potentially a greater public health concern among women than among men [ 48 ].

Skeletal muscle strength (force-generating capacity) also gets reduced with ageing [ 45 , 46 ] depending upon genetic, dietary and, environmental factors as well as lifestyle choices. This reduction in muscle strength causes problems in physical mobility and activity of daily living. The total amount of muscle fibres is decreased due to a depressed productive capacity of cells to produce protein. There is a decrease in the size of muscle cells, fibres and tissues along with the total loss of muscle power, muscle bulk and muscle strength of all major muscle groups like deltoids, biceps, triceps, hamstrings, gastrocnemius (calf muscle), and so on. Wear and tear or wasting of the protective cartilage of joints occurs. The cartilage normally acts as a shock absorber and a gliding agent that prevents the friction injuries of the bone. There are stiffening and fibrosis of connective tissue elements that reduce the range of motion and affect the movements by making them less efficient. As part of the normal cell division process, telomere shortening occurs. DNA is more exposed to chemicals, toxins and waste products produced in the body. This whole process increases the vulnerability of cells.

With ageing, toxins and chemicals build up within the body and tissues. As a whole, this damages the integrity of muscle cells. Physical activity also decreases with age, due to a change in lifestyle. Somehow, the physiological changes of the muscles are aggravated by age-related neurological changes [ 49 ]. Most of the muscular activities become less efficient and less responsive with ageing as a result of a decrease in the nervous activity and nerve conduction.

A study was done by Williams et al. [ 50 ], who evaluated the muscle samples from both elderly and young adults and suggested that limb muscles are 25–35% shorter and less responsive in elderly healthy individuals when compared to young adults. In addition, the overall fat content of muscles was also higher in elderly population, suggesting transformation in the normal remodelling with age. Age-related musculoskeletal changes are much more prominent in fast-twitch muscle fibres as compared to slow-twitch muscle fibres. With ageing, the total water content of the tissue decreases and loss of hydration also adds to the inelasticity and stiffness. Alterations in the basal metabolic rate and slowing metabolism (as part of the physiological ageing process) result in muscle changes. This leads to the replacement of proteins with fatty tissue (that makes muscle less efficient).

Hormonal disorders can affect the metabolism of bones as well as muscles. Research suggests that menopause in women marks the aggravation in the deterioration of musculoskeletal changes due to lack of oestrogen that is required for the remodelling of bones and soft tissues. Certain systemic conditions like vascular disorders or metabolic disorders, in the case of diabetes, affect the remodelling of tissues as the rate or volume of nutritional delivery for the regeneration of cells is compromised. It is very important to control the pathological processes to optimise healing and repairing the potential of the musculoskeletal system. Essential vitamins like vitamin D and vitamin C play major roles in the functional growth of muscles and bones. Lack of certain minerals like calcium, phosphorus and chromium can be the result of age-related digestive issues. As such, it results in imbalance in the production of certain hormones like calcitonin and parathyroid that regulate the serum concentration of vitamins and minerals (due to tumours that are highly prevalent in elderly) or it causes a decreased absorption from the gut.

Age-related deterioration of muscular strength and balance control mechanisms has been associated with a reduced performance on functional tasks [ 51 , 52 , 53 ]. Comparing the isometric strength levels of the same muscle group, the loss of strength begins sooner among women than among men. It is reported that women are weaker than men in the absolute strength of various muscle groups in all stages of life. Various studies state that women have a longer life span, so the prevalence of disability among women is also more compared with men and it is marked with advancing age [ 54 , 55 , 56 ].

4. Body composition changes in old age

The human body is made up of fat, lean tissue (muscles and organs), bones and water. After the age of 40, people start losing their lean tissue. Body organs like liver, kidneys and other organs start losing some of their cells. This decline in muscle mass is associated with weakness, disability and morbidity [ 57 , 58 ].

The tendency to become shorter occurs among the different gender groups and in all races. Height loss is associated with ageing changes in the bones, muscles and joints. Studies show that people typically lose almost one-half inch (about 1 cm) every 10 years after age 40 [ 59 ]. Height loss is even more rapid after age 70. These changes can be prevented by following a healthy diet, staying physically active and preventing and treating bone loss [ 60 , 61 ].

Changes in the total body weight vary for men and woman, as men often gain weight until about age 55 and then begin to lose weight later in life. This may be related to a drop in the male sex hormone testosterone. Women usually gain weight until age 67–69 and then begin to lose weight. Weight loss later in life occurs partly because fat replaces lean muscle tissue and fat weighs less than muscle [ 60 ]. Studies have also shown that older people may have almost one-third more fat compared to when they were younger. Fat tissue builds up towards the centre of the body, including around the internal organs [ 60 , 62 , 63 ].

5. Obesity in elderly: prevalence

Today, as standards of living continue to rise, weight gain is posing a growing threat to the health of inhabitants from countries all over the world. Obesity is a chronic disease, prevalent in both developed and developing countries, and it is affecting all age groups. Indeed, it is now so common that it is replacing the more traditional public health concerns, such as infectious diseases and undernutrition, as the most common and significant contributors of ill health [ 64 , 65 , 66 , 67 ] ( Figure 3 ).

Prevalence of obesity among elderly aged 60 years and above, by sex: The United States, 2013. Source: [ 68 ].

As per World Health Organisation (WHO), globally, approximately 2.3 billion elderly people are overweight and more than 700 million elderly people are obese [ 68 ]. Most elderly belonging to the middle and high socio-economic groups are prone to obesity and complications related to obesity, due to sedentary lifestyles and a reduced physical mobility [ 69 ]. Obesity is considered as one of the major risk factors which causes the onset and increases the severity of non-communicable diseases (NCDs). It is a worldwide health problem, affecting elderly from both developed and developing countries. In elderly, obesity contributes to the early onset of chronic morbidities and functional impairments which lead to premature mortality [ 70 ].

5.1. Obesity among elderly: developed countries

The population in developed countries have proportionally a greater number of older adults living to older ages, and the prevalence of obesity is rising progressively, even among this age group [ 71 ].

The prevalence of obesity among elderly belonging to United States ranges from 42.5% in women to 38.1% in men, belonging to the age group 60–79 years. The prevalence differs for the elderly belonging to the age group 80 years and above, that is, 19.5% for females and 9.6% for males [ 72 , 73 , 74 ].

Comparatively, the prevalence of obesity in Europe is slightly lower but it is still a significant health issue. The prevalence of obesity among elderly in the United Kingdom is 22% among women and 12% among men aged 75 years or older [ 70 , 75 , 76 , 77 ]. These statistics bode ill as the proportion of world’s elderly population is growing rapidly ( Figure 4 ).

Trends in weight by age cohort, 1980–2000 (Australia). Source: Bennett et al. [ 81 ].

In Australia, the percentage of weight gain has been so high that instead of losing weight with an increase in life, men and women aged 60–70 weigh more on average than they did when they were 20 years younger ( Figure 5 ). Australian studies show that the prevalence of obesity among elderly has increased in the age group of 60–69 years at about 24% for males and 30% for females, whereas it is less common among the elderly belonging to age group 80 years and above [ 78 , 80 ]. Studies show that the percentage of Australian elderly reporting increased abdominal fat is markedly increasing over the years. Based on waist circumference, more than 30% of elderly males and 44% of elderly females in Australia are currently at a substantially increased risk of NCDs [ 78 , 80 , 81 ].

Worldwide prevalence of obesity among elderly women and men with BMI of ≥30 kg/m 2 . Source: OECD [ 79 ]. Analysis of health survey data.

Studies from the Netherlands show that obesity was present in 18% of men and 20% of women belonging to the age group of 60 years and above [ 82 ]. Also, the increase in waist circumference ranged from 40% among males to 56% among females [ 82 , 83 ].

In France, studies show that the prevalence of obesity among elderly was relatively stable during early years (1980–1991), 6.4–6.5% in males and 6.3–7.0% among females [ 83 ], but studies from recent years [ 84 , 85 ] have highlighted a sharp increase in obese elderly, 19.5% for both males and females; this prevalence rate decreased gradually after 70 years of age, that is, from 19.5 to 13.2% [ 86 ]. The Scottish Health Survey shows that in 10 years (2003–2013), the prevalence of obesity has increased as the body mass index (BMI) continues to rise in people 60–70 years of age, especially among females [ 87 ]. In this same period, there was an increased curve shown for the waist circumference (5–10 cm) in both the sexes between 50 and 70 years of age. This inappropriate increase in waist circumference and a slight increase in BMI in the Scottish Health Survey may indicate a substantial gain in visceral fat mass and loss of lean tissue that predisposes to ill health in the obese elderly [ 88 , 89 ].

In Spain, 35% of subjects aged 65 years or older suffered from obesity (30.6% of males and 38.3% of females) and 61.6% had an increased waist circumference (50.9% of males and 69.7% of females) [ 88 ].

5.2. Prevalence of obesity: developing countries

Over the past years, obesity among elderly was considered as a problem only in high-income countries, but the trend is changing now; excess weight, as well as obesity, is dramatically increasing in low-income and middle-income countries as well, particularly in urban settings [ 90 ]. Various studies show a significant change in the mean body weight, physical activity and diet along with progressive economic development in developing countries. Possibilities are high that obesity and its co-morbidities will continue to affect an increasing number of populations in these regions. Lifestyle and environmental factors are acting in a synergistic manner to fuel the obesity epidemic. As per WHO estimates, there is a decline in undernourished population across the world, whereas the overnourished population has increased to 1.2 billion [ 90 ]. A WHO report shows that more than 1 billion elderly are overweight and 300 million are obese. The problem of obesity is increasing in the developing world with more than 115 million people suffering from obesity-related problems [ 90 ]. The obesity rate has increased threefold or more since 1980 in the Middle East, the Pacific Islands and India [ 91 , 92 ]. However, the prevalence of obesity is not as high in all developing countries, like China and some African nations [ 93 ].

As per the WHO report, the prevalence of overweight and obese elderly in China was 19.0 and 2.9%, respectively. However, the prevalence has increased over the past years; in the latest study, the prevalence of overweight and obesity among elderly was 21.0 and 7.4% [ 94 , 95 ]. There was a slight increase in the prevalence of overweight and obesity among women than among men in China.

According to WHO estimates, among all Gulf regions, Kuwait ranked number one with the highest prevalence of overweight and obesity (78.8%) among elderly (60 years and above) [ 92 ]. Worldwide, Kuwait is ranked 11th, that is, the highest in obesity among the Arab countries and the Middle East [ 93 , 96 ]. Studies from Sri Lanka show a prevalence rate of 25.2% for overweight and 9.2% for obesity. The prevalence of central obesity among elderly was highest at 26.2% [ 97 , 98 ]. The prevalence of overweight and obesity in Brazil was 41.8% for females and 23.4% for males. According to the prevalence studies of obesity among elderly in Nigeria [ 99 ], overweight among elderly ranged from 20.3 to 35.1% and obesity ranged from 8.1 to 22.2%. WHO reported that the prevalence of obesity in Sub-Saharan African countries ranged between 3.3 and 18.0% and that obesity has become a leading risk factor for diabetes mellitus and cardiovascular diseases in the urban areas of Africa [ 93 , 99 ]. The situation can get worse within a decade if the present trend continues and overweight could emerge as the single most important public health problem in adults. Overweight or obesity may not be a specific disease but it is certainly considered as a major contributory factor leading to various degenerative diseases in adult life. Prevention and control of this problem must, therefore, claim priority attention [ 100 ].

As per a study done in Delhi on urban elderly, nearly 14% of men and more than 50% of women belonging to what may be a higher-income group (HIG) were overweight (BMI >25) and obese (BMI >30) [ 101 ]. The prevalence of abdominal obesity among the elderly group was also reported as high. Assuming that the HIG in India number is around 100 million (half the number of the middle class), it may be computed that there are roughly 40–50 million overweight subjects belonging to the HIG in the country today. Visweswara et al. [ 102 ] studied females of Hyderabad (60 years and above) belonging to the high socio-economic status and reported the prevalence rate of obesity as 36.3%. Gopinath et al. [ 103 ] studied urban elderly in Delhi and reported the rate of prevalence of obesity as 33.4%. A study done in the Union Territory of Chandigarh showed an increase in BMI (>25) resulting in the high prevalence rate of overweight (33.14%) and obesity (7.54%) among elderly [ 104 , 105 ].

6. Causes of obesity among elderly

The relationship between energy intake and energy expenditure is an important determinant of body fat mass. Obesity occurs when the consumption of calories is more than the calorie expenditure. The possible causes of obesity are depicted in Figure 6 . Various studies indicate that how much we eat does not decline with advancing age; therefore, it is likely that a decrease in energy expenditure particularly in the beginning of old age (50–65 years) contributes to the increase in body fat as we age [ 62 , 106 ]. At the age of 65 years and above, hormonal changes cause an accumulation of fat. Ageing is associated with a decline in the secretion of growth hormone, serum testosterone, resistance to leptin and a reduced responsiveness to thyroid hormone [ 107 ]. Studies show that resistance to leptin could cause a decrease in the ability to regulate appetite downward [ 74 ]. Several other genetic, environmental and social factors contribute to obesity among elderly.

Possible causes of obesity. Source: La Berge [ 108 ].

6.1. Genetic factors

Science does show a link between obesity and heredity [ 109 ]. Various studies indicate that obesity is related to the inherited genes and there is a link between obesity and heredity [ 110 , 111 , 112 , 113 ]. According to a study, visceral fat is more influenced by the genotype than subcutaneous fat [ 114 ].

6.2. Environmental and sociological factors

Like genetics, environment also has a major role to play in obesity. The food we consume, physical activity and lifestyle behaviour are all influenced by the environment. For example, the adoption of modern diet over traditional diet, the trend towards ‘eating out’ rather than preparing food in the home, the development of high-rise buildings that often lack sidewalks and a deficit of readily accessible recreation areas are some of the common environmental factors associated with obesity.

Poverty and low education level also appeared as a reason for obesity among elderly. Studies state that the lack of nutritional knowledge, purchase of low-cost fat and organ meat are also associated with overweight and obesity. Poor hygienic conditions also appeared as a major reason [ 114 ].

6.3. Other causes of obesity

Other health issues and illnesses that are associated with obesity and weight gain are hyperthyroidism, polycystic ovary syndrome, Cushing’s syndrome and depression [ 2 ]. Obese elderly are more likely to report symptoms of depression, such as hopelessness, sadness or worthlessness [ 115 ]. Sleep plays a major role. Lack of sleep contributes to obesity [ 106 ]. Certain drugs, such as antidepressants and steroids, may stimulate appetite or cause water retention or reduce the metabolic rate [ 82 ], causing an increase in weight. Health issues like arthritis and joint pain decrease mobility and activity intolerance, contributing to obesity [ 116 ]. Joint pain decreases mobility, and activity intolerance may lead to weight gain because of a decreased activity. Older adults are more likely than younger adults to experience functional limitations associated with chronic illnesses that may begin a stress-pain-depression cycle that can result in lifestyle patterns leading to obesity [ 117 ]. Finally, the complex relationship between lifestyle pattern and functional ability merits attention as a contributor to obesity [ 93 ].

7. Conclusion

In developing countries, as compared to developed countries, gerontology has drawn comparatively lesser attention. This is because the increased life expectancy of elderly resulting in a demographic transition which developing countries are witnessing today has already been faced by developed countries, several decades back. However, in recent years with a rising percentage of elderly population, epidemiologists, researchers, demographers and clinicians have focussed their attention towards elderly care health issues and various problems associated with ageing and numerous implications of this demographic transition.

Elderly face various problems and require a multi-sectoral approach involving inputs from various disciplines of health, psychology, nutrition, sociology and social sciences.

Conflict of interest

There is no conflict of interest.

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The Evolution of Aging

Aging is an Evolutionary Paradox

Why do we age and die? Aging, or senescence as it is sometimes called, is an inevitable progressive deterioration of physiological function with increasing age, demographically characterized by an age-dependent increase in mortality and decline of fecundity (Rose 1991, Bronikowksi & Flatt 2010, see Figure 1). This poses an evolutionary paradox: natural selection designs organisms for optimal survival and reproductive success (Darwinian fitness), so why does evolution not prevent aging in the first place?

Figure 1 a) Portrait of Joan Riudavets Moll (15 December 1889 – 5 March 2004), a Spanish supercentenarian who died at age 114. b) One manifestation of aging in elderly humans are cataracts, a clouding of the eye lens. c) Another symptom of aging in humans is atherosclerosis, a thickening of the artery wall. Shown here is a case of severe atherosclerosis of the aorta. Image a) courtesy of Wikipedia. Image b) courtesy of Rakesh Ahuja, M.D. Image c) courtesy of Dr. Edwin P. Ewing, Jr./CDC.

For centuries, beginning with Aristotle, scientists and philosophers have struggled to resolve this enigma. The Roman poet and philosopher Lucretius, for example, argued in his De Rerum Natura (On the Nature of Things) that aging and death are beneficial because they make room for the next generation (Bailey 1947), a view that persisted among biologists well into the 20th century. The famous 19th century German biologist, August Weissmann, for instance, suggested – similar to Lucretius – that selection might favor the evolution of a death mechanism that ensures species survival by making space for more youthful, reproductively prolific individuals (Weissmann 1891). But this explanation turns out to be wrong. Since the cost of death to individuals likely exceeds the benefit to the group or species, and because long-lived individuals leave more offspring than short-lived individuals (given equivalent reproductive output), selection would not favor such a death mechanism. A more parsimonious evolutionary explanation for the existence of aging therefore requires an explanation that is based on individual fitness and selection, not on group selection. This was understood in the 1940's and 1950's by three evolutionary biologists, J.B.S. Haldane, Peter B. Medawar and George C. Williams, who realized that aging does not evolve for the "good of the species". Instead, they argued, aging evolves because natural selection becomes inefficient at maintaining function (and fitness) at old age. Their ideas were later mathematically formalized by William D. Hamilton and Brian Charlesworth in the 1960's and 1970's, and today they are empirically well supported. Below we review these major evolutionary insights and the empirical evidence for why we grow old and die. For further in-depth coverage of the evolution of aging we point the reader to Rose (1991), Hughes & Reynolds (2005), Promislow & Bronikowski (2006), Flatt & Schmidt (2009), and references therein. Also see Rauschert (2010) and Shefferson (2010) in Nature Education Knowledge .

The Force of Selection Declines with Age

As mentioned above, the key conceptual insight that allowed Medawar, Williams, and others, to develop the evolutionary theory of aging is based on the notion that the force of natural selection, a measure of how effectively selection acts on survival rate or fecundity as a function of age, declines with progressive age (see Hamilton 1966, Charlesworth 2000, Rose et al . 2007) (Figure 2). This was first noted, though not formally analyzed, by Fisher in his famous book The Genetical Theory of Natural Selection (1930), and both Haldane (1941) and Medawar (1946, 1952) came to the same conclusion. Haldane (1941) proposed that the declining strength of selection with age might explain the relatively high prevalence of the dominant allele causing Huntington’s disease: he speculated that, since Huntington's typically only affects people beyond age 30, such a disease would not have been efficiently eliminated by selection in ancestral, pre-modern populations because most people would already have died well before they could experience this late-onset disease. Thus, the disease would not have been "seen" by, or subject to, selection. Based on Fisher's and Haldane's ideas, Medawar (1946, 1952) worked out the first complete verbal and graphical model of how aging evolves (also see next section). The gist of Medawar's argument is as follows. First, for most organisms, the natural world is dangerous since it abounds with competitors, predators, pathogens, accidents, and other hazards. It follows from this that in natural populations most individuals die or get killed before they can grow old and suffer the symptoms of aging: thus, individuals have a very small overall probability of being alive and reproductive at an advanced age (e.g., Moorad & Promislow 2010). Second, the strength of natural selection declines with increasing age (Figure 2), such that selection ignores the performance of individuals late in life. As a consequence, selection is unable to favor beneficial effects, or to counteract deleterious effects, when these effects are expressed at advanced ages. For example, if a beneficial or deleterious mutation occurs only after reproduction has ceased, then it will not affect fitness (reproductive success) and can therefore not be efficiently selected for or against. However, even if a mutation occurs earlier, say during the reproductive period, its effects may not be visible to selection since, if extrinsic, environmentally imposed mortality is high, individuals that could express the mutation are likely to be dead already.

Medawar (1946, 1952) and Williams (1957) realized that these deductions, later mathematically expressed by Hamilton (1966, also see Rose et al . 2007), would open the door for the evolution of aging.

The Mutation Accumulation Hypothesis

Following the logic outlined above, Medawar (1946, 1952) reasoned that, if the effects of a deleterious mutation were restricted to late ages, when reproduction has largely stopped and future survival is unlikely, carriers of the negative mutation would have already passed it on to the next generation before the negative late-life effects would become apparent. In such a situation, natural selection would be weak and inefficient at eliminating such a mutation, and over evolutionary time such effectively neutral mutations would accumulate in the population by genetic drift, which in turn would lead to the evolution of aging. This is known as Medawar's mutation accumulation (MA) hypothesis (Figure 3A). The effects of such a mutation accumulation process would only become manifest at the organismal level after the environment changes such that individuals experience less extrinsic mortality (e.g., due to decreased predation) and thus live to an age where they actually express the symptoms of aging.

Medawars' MA hypothesis was later put on firm mathematical ground by Charlesworth (1994, 2001). Several experimental studies, mainly in fruit flies ( Drosophila melanogaster ), have found – somewhat limited – empirical support for the occurrence of MA (see Hughes & Reynolds 2005, Charlesworth 1994, Hughes et al . 2002 for a discussion).

The Antagonistic Pleiotropy Hypothesis

In an influential paper published in Evolution, George C. Williams (1957) took Medawar's ideas a step further. If it is true that selection cannot counteract deleterious effects at old age, he argued, then mutations or alleles might exist that have opposite, pleiotropic effects at different ages: genetic variants that on the one hand exhibit beneficial effects on fitness early in life, when selection is strong, but that on the other hand have deleterious effects late in life, when selection is already weak. This idea is known today as the antagonistic pleiotropy (AP) hypothesis for the evolution of aging (see Rose 1991, Flatt & Promislow 2007, Figure 3B). Williams pointed out that, if the beneficial effects of such mutations early in life outweigh their deleterious effects at advanced age, such genetic variants would be favored and enriched in a population, thus leading to the evolution of aging. Thus, under Williams' hypothesis, the evolution of aging can be seen as a maladaptive byproduct of selection for survival and reproduction during youth. A fundamental corollary of Williams’ AP hypothesis is that early fitness components such as reproduction should genetically trade-off with late fitness components such as survival at old age, so that, for example, genotypes with high early fecundity should be shorter lived than those with low reproduction (e.g., Williams 1957, Rose 1991, Charlesworth 1994, Hughes & Reynolds 2005). In a somewhat similar vein, Kirkwood’s 1977 "disposable soma " (DS) hypothesis predicts that the optimal level of investment into somatic maintenance and repair will evolve to be below that required for indefinite survival. The idea here is that the evolution of a higher investment is unlikely to pay off since the return from such an investment may never be realized due to extrinsic mortality. Moreover, investment into reproduction – or early fitness components in general – might withdraw limited resources that could otherwise be used for somatic maintenance and repair. Such resource allocation trade-offs can thus been seen as a physiological extension of Williams' AP model. Although the relative frequency of MA versus AP is still debated (both may typically go hand in hand - see also Moorad & Promislow 2009), there is robust evidence today for the existence of fitness trade-offs that are consistent with the notion of AP (for a recent discussion of the positive evidence see Flatt & Promislow 2007, and Flatt 2011, but also see Moorad & Promislow 2009). Whether such trade-offs are physiologically caused by competitive energy or resource allocation – as would be expected under the DS hypothesis – remains somewhat controversial, but the trade-offs themselves are well established (see Flatt 2011). Most importantly, the kinds of trade-offs postulated by Williams, have been found at the evolutionary level: for example, fruit flies that were artificially selected for increased late-life reproductive success were found to be long-lived at the expense of reduced early fecundity in several, now classical, experiments in the labs of Michael Rose and Leo Luckinbill (Rose & Charlesworth 1980, Rose 1984, Luckinbill et al . 1984). These elegant experiments represent the first solid empirical tests of the evolutionary theory of aging (Rose 1991). The classical evolutionary theory of aging has therefore two fundamental cornerstones: MA and AP. However, it is worth noting that both models are conceptually very similar: under MA, aging evolves through the accumulation of effectively neutral mutations with deleterious late-life effects, whereas, under AP, aging occurs due to mutations with beneficial early- and deleterious late-life effects. In reality, probably both types of mutations occur in populations, yet their relative frequencies remain unknown. Furthermore, the age distribution of mutational effects may be much more complicated than these two scenarios suggest (e.g., Moorad & Promislow 2008).

Evolution of Lifespan

Figure 4: Variation in lifespan among different organisms. Different species vary dramatically in how long they life. The dome-shelled Galápagos giant tortoise ( Geochelone elephantopus ) can reach an age of about 180 years (a), whereas some mayfly species (belonging to the insect order Ephemeroptera) die after about 30 minutes (b). Even older than giant tortoises are certain trees, such as the yew ( Taxus baccata ), with some specimens between 4,000 and 5,000 years old (c). A few other organisms, such as freshwater polyps of the genus Hydra , are thought to age at a negligible rate or to be even potentially immortal, although this is still somewhat controversial (d). Image a) courtesy of Matthew Field. Image b) courtesy of Fritz Geller-Grimm. Image c) courtesy of Wikipedia. Image d) courtesy of Przemyslaw Malkowski.

Different organisms vary dramatically in their lifespan (Figure 4). Obviously, aging negatively affects the duration of life since it increases the risk of death. These intrinsic, maladaptive effects of aging, unchecked by selection, are, however, not the only factors affecting the length of life. Independent of whether aging occurs or not, reproductive lifespan can evolve adaptively in response to selection for increased reproductive success (Stearns 1992). A longer lifespan normally implies increased reproductive success, and factors such as low adult mortality (permitting more reproductive events per lifetime), high juvenile mortality (making it necessary for adults to reproductively compensate for such loss), and high variation in juvenile mortality from one bout of reproduction to the next (increasing uncertainty in reproductive success and requiring reproductive compensation as well) therefore all tend to lengthen reproductive lifespan (Stearns 1992). These lifespan promoting effects of selection are balanced by those that tend to increase adult mortality relative to juvenile mortality. Consequently, if extrinsic, environmentally imposed adult mortality is high, selection becomes weak, thereby allowing the evolution of higher levels of intrinsic mortality (i.e., aging). Moreover, even though selection might favor increased reproductive success, and thus a longer reproductive lifespan, the length of life might be limited by intrinsic trade-offs between reproduction and survival caused by AP. Thus, the evolution of lifespan can be viewed as a balance between selection for increased reproductive success and the factors that increase the intrinsic age-dependent components of mortality (Stearns 1992). These ideas have been empirically tested and corroborated by several researchers. For example, using an elegant experimental evolution design, Stearns et al. (2000) exposed fruit flies to either high or low levels of extrinsic adult mortality (HAM versus LAM) and found that LAM flies evolved significantly lower levels of intrinsic mortality relative to HAM flies: in other words, HAM flies evolved more rapid aging than LAM flies. Given that there is ample genetic variation for lifespan and the rate of aging, and given that aging can readily evolve by MA and/or AP, is aging then likely to be universal among species? Clearly, there is a remarkable amount of variation in lifespan among different species, including some extremely short-lived as well long-lived species (e.g., Finch 1990, Figure 4). A lot of this diversity in lifespan can be quite readily explained by variation in the levels of extrinsic mortality and the evolution of different optimal lengths of reproductive life, including the existence of semelparous organisms that reproduce only once and then die (Stearns 1992). For example, species that are well protected from predators – for example, those that have a shell, can fly, or are poisonous – tend to live longer than related, less well-protected species (e.g., Austad & Fischer 1991, Blanco & Sherman 2005). But are there immortal organisms? Although examples of organisms that age very slowly are well known (e.g., Finch 1990, see Figure 4), it is not yet sufficiently clear whether there exist species that truly do not age at all. Bacteria are a good case in point. For a long time it was thought that bacteria do not age. Indeed, one of Williams' (1957) strongest assertions about the evolution of aging was that only organisms with a separation of germ line and soma should age. In such organisms, the germ line is maintained indefinitely, but the aging soma is “disposable” after fulfilling its reproductive role. Bacteria, by contrast, do not exhibit a clear delineation into germ line and soma, and should therefore be immortal. More important than this lack of a clear germ line/soma distinction, however, is the fact that prokaryotes, protozoans, algae, and symmetrically dividing unicells, do not have clearly delineated age classes (Rose 1991, Partridge & Barton 1993). In symmetrically dividing unicells, for example, individuals should not age because parent and offspring are phenotypically indistinguishable – it is impossible to determine old from young, and age is thus invisible to selection. By the same logic, aging should exist in asymmetrically reproducing organisms where aging parents are phenotypically distinct from offspring. Indeed, an asymmetrically dividing bacterium has recently been found to show senescence (Ackermann et al . 2003). Remarkably, however, even the symmetrically dividing E. coli ages: it shows subcellular mother-offspring asymmetry, delineating age classes upon which selection can act to produce senescence (Stewart et al . 2005). Moreover, Ackermann et al. (2007) modeled the origin of aging in the history of life and found that, even when cells divide symmetrically, unicellulars readily evolve a state of asymmetric, unequal distribution of cellular damage among daughter cells. However, as soon as such an asymmetry evolves, aging evolves. Thus, aging – despite remarkable variation in the duration of life among different species – might be a fundamental and inevitable property of cellular life.

We have introduced what evolutionary biologists think about the evolution of aging. Today, it is clear that aging is not a positively selected, programmed death process, and has not evolved for "the good of the species". Instead, aging is a feature of life that exists because selection is weak and ineffective at maintaining survival, reproduction, and somatic repair at old age. Based on the observation that the force of selection declines as a function of age, two main hypotheses have been formulated to explain why organisms grow old and die: the mutation accumulation (MA) and the antagonistic pleiotropy (AP) hypotheses. Under MA, aging evolves because selection cannot efficiently eliminate deleterious mutations that manifest themselves only late in life. Under AP, aging evolves as a maladaptive byproduct of selection for increased fitness early in life, with the beneficial early-life effects being genetically coupled to deleterious late-life effects that cause aging. Aging clearly shortens lifespan, but lifespan is also shaped by selection for an increased number of lifetime reproductive events. The evolution of lifespan is therefore a balance between selective factors that extend the reproductive period and components of intrinsic mortality that shorten it. Whether there exist truly immortal organisms is controversial, and recent evidence suggests in fact that aging might be an inevitable property of all cellular life.

Fecundity - Fecundity is defined as the number of offspring (e.g., gametes, eggs, propagules) or the rate of offspring production (e.g., the number of eggs laid per female per unit time). Fitness - Fitness (sometimes also called Darwinian fitness) is a measure of the relative expected contribution of a genotype (or phenotype) to future generations. The easiest way to think about fitness is in terms of lifetime reproductive success of a genotype (or phenotype) relative to other such types in a population. Note that natural selection can be defined as heritable variation among genotypes in fitness. Germ line - The germ line is a specialized lineage of stem cells that gives rise to gametes (eggs, sperm). Parsimony, parsimonious - The principle of parsimony (sometimes also called Occam's razor) states that when choosing among several competing explanations (or models, or hypotheses) to explain a particular phenomenon it is often best to select the simplest (i.e., making the fewest assumptions). If new evidence becomes available the explanation can be re-evaluated against the facts: if the simplest explanation still explains the facts best, it should be retained. However, if the new evidence suggests that a more complex explanation has better explanatory power, then the simpler alternative should be discarded. Pleiotropy, pleiotropic - Pleiotropy means that a gene (or allele or mutation) affects two or more traits (or processes or functions). Semelparity, semelparous - Semelparous organisms are those that only have one reproductive event per lifetime (independent of how many offspring are produced in this single event). Semelparity is sometimes also called "big bang" reproduction. Senescence - Senescence is essentially synonymous with aging, i.e. the age-dependent decline in physiological function, ultimately leading to death. At the demographic level, this physiological deterioration is manifest as a decline in fecundity and an increase in mortality with increasing age. Soma - The non-reproductive parts of the body (and its organs, tissues, and cells) that carry out all biological functions except reproduction. The soma is typically contrasted with the germ line, i.e. the lineage of cells that gives rise to gametes, and the reproductive organs.

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What Is the Genetic Theory of Aging?

How Genes Affect Aging and How You May "Alter" Your Genes

Your DNA may predict more about you than the way you look. According to the genetic theory of aging, your genes (as well as mutations in those genes) are responsible for how long you'll live. Here's what you should know about genes and longevity, and where genetics fits in among the various theories of aging.

Genetic Theory of Aging

The genetic theory of aging states that lifespan is largely determined by the genes we inherit. According to the theory, our longevity is primarily determined at the moment of conception and is largely reliant on our parents and their genes.  

The basis behind this theory is that segments of DNA that occur at the end of chromosomes, called telomeres , determine the maximum lifespan of a cell. Telomeres are pieces of "junk" DNA at the end of chromosomes which become shorter every time a cell divides. These telomeres become shorter and shorter and eventually, the cells cannot divide without losing important pieces of DNA.  

Before delving into the tenets of how genetics affects aging, and the arguments for and against this theory, it's helpful to briefly discuss the primary categories of aging theories and some of the specific theories in these categories. At the current time, there is not one theory or even one category of theories that can explain everything we observe in the aging process.

Theories of Aging

There are two primary categories of aging theories which differ fundamentally in what can be referred to as the "purpose" of aging. In the first category, aging is essentially an accident; an accumulation of damage and wear and tear to the body which eventually leads to death. In contrast, programmed aging theories view aging as an intentional process, controlled in a way that can be likened to other phases of life such as puberty.

Error theories include several separate theories including:

• Wear and tear theory of aging  
• Rate of living theory of aging
• Protein cross-linking theory of aging  
• Free radical theory of aging
• Somatic mutation theory of aging  

Programmed theories of aging are also broken down into different categories based on the method by which our bodies are programmed to age and die.

• Programmed longevity - Programmed longevity claims that life is determined by a sequential turning on and off of genes.  
• Endocrine theory of aging
• Immunological theory of aging  

There is significant overlap between these theories and even categories of aging theories.

Genes and Bodily Functions

Before discussing the key concepts related to aging and genetics, let's review what our DNA is and some of the basic ways in which genes affect our lifespan.

Our genes are contained in our DNA which is present in the nucleus (inner area) of each cell in our bodies. (There is also mitochondrial DNA present in the organelles called mitochondria which are present in the cytoplasm of the cell.) We each have 46 chromosomes making up our DNA, 23 of which come from our mothers and 23 which come from our fathers. Of these, 44 are autosomes, and two are the sex chromosomes, which determine if we are to be male or female. (Mitochondrial DNA, in contrast, carries much less genetic information and is received from only our mothers.)

Within these chromosomes lie our genes, our genetic blueprint responsible for carrying the information for every process which will take place in our cells. Our genes can be envisioned as a series of letters that make up words and sentences of instructions. These words and sentences code for the manufacturing of proteins that control every cellular process.

If any of these genes are damaged, for example, by a mutation that alters the series of "letters and words" in the instructions, an abnormal protein may be manufactured, which in turn, performs a defective function. If a mutation occurs in proteins that regulate the growth of a cell, cancer may result. If these genes are mutated from birth, various hereditary syndromes may occur. For example, cystic fibrosis is a condition in which a child inherits two mutated genes controlling a protein that regulates channels responsible for the movement of chloride across cells in the sweat glands, digestive glands, and more. The result of this single mutation results in a thickening of mucus produced by these glands, and the resultant problems which are associated with this condition.

How Genes Impact Lifespan

It doesn't take an elaborate study to determine that our genes play at least some role in longevity. People whose parents and ancestors have lived longer, tend to live longer and vice versa. At the same time, we know that genetics alone are not the sole cause of aging. Studies looking at identical twins reveal that there is clearly something else going on; identical twins who have identical genes do not always live an identical number of years.

Some genes are beneficial and enhance longevity. For example, the gene that helps a person metabolize cholesterol would reduce a person's risk of heart disease.

Some gene mutations are inherited and may shorten lifespan. However, mutations also can happen after birth, since exposure to toxins, free radicals and radiation can cause gene changes. (Gene mutations acquired after birth are referred to as acquired or somatic gene mutations.) Most mutations are not bad for you, and some can even be beneficial. That's because genetic mutations create genetic diversity, which keeps populations healthy. Other mutations, called silent mutations, have no effect on the body at all.

Some genes, when mutated are harmful, like those that increase the risk of cancer. Many people are familiar with the BRCA1 and BRCA2 mutations which predispose to breast cancer. These genes are referred to as tumor suppressor genes which code for proteins that control the repair of damaged DNA (or the elimination of the cell with damaged DNA if repair is not possible.)

Various diseases and conditions related to heritable gene mutations can directly impact lifespan. These include cystic fibrosis, sickle cell anemia, Tay-Sachs disease, and Huntington's disease, to name a few.

Key Concepts in the Genetic Theory of Aging

The key concepts in genetics and aging include several important concepts and ideas ranging from telomere shortening to theories about the role of stem cells in aging.

At the end of each of our chromosomes lies a piece of "junk" DNA called telomeres. Telomeres do not code for any proteins but appear to have a protective function, keeping the ends of DNA from attaching to other pieces of DNA or forming a circle. Each time a cell divides a little more of a telomere is snipped off. Eventually. there is none of this junk DNA left, and further snipping can damage the chromosomes and genes so that the cell dies.

In general, the average cell is able to divide 50 times before the telomere is used up (the Hayflick limit). Cancer cells have figured out a way to not remove, and sometimes even add to, a section of the telomere. In addition, some cells such as white blood cells do not undergo this process of telomere shortening. It appears that while genes in all of our cells have the code word for the enzyme telomerase which inhibits telomere shortening and possibly even results in lengthening, the gene is only "turned on" or "expressed" as geneticists say, in cells such as white blood cells and cancer cells. Scientists have theorized that if this telomerase could somehow be turned on in other cells (but not so much that their growth would go haywire as in cancer cells) our age limit could be expanded.

Studies have found that some chronic conditions such as high blood pressure are associated with less telomerase activity whereas a healthy diet and exercise are linked with longer telomeres. Being overweight is also associated with shorter telomeres.

Longevity Genes

Longevity genes are specific genes that are associated with living longer. Two genes that are directly associated with longevity are SIRT1 (sirtuin 1) and SIRT2.   Scientists looking at a group of over 800 people age 100 or older, found three significant differences in genes associated with aging.

Cell Senescence

Cell senescence refers to the process by which cells decay over time. This can be related to the shortening of the telomeres or the process of apoptosis (or cell suicide) in which old or damaged cells are removed.  

Pluripotent stem cells are immature cells that have the potential to become any type of cell in the body. It is theorized that aging may be related to either the depletion of stem cells or the loss of the ability of stem cells to differentiate or mature into different kinds of cells. It's important to note that this theory refers to adult stem cells, not embryonic stem cells. Unlike embryonic stem cells, adult stem cells cannot mature into any type of cell but rather only a certain number of cell types. Most cells in our bodies are differentiated, or fully mature, and stem cells are only a small number of the cells present in the body.

An example of a tissue type in which regeneration is possible by this method is the liver. This is in contrast to brain tissue which usually lacks this regenerative potential. There is now evidence that stem cells themselves may be affected in the aging process, but these theories are similar to the chicken-and-the-egg issue. It's not certain of aging occurs due to changes in stem cells, or if instead, changes in stem cells are due to the process of aging.

Epigenetics

Epigenetics refers to the expression of genes. In other words, a gene may be present but can either be turned on or turned off. We know that there are some genes in the body that are turned on for only a certain period of time. The field of epigenetics is also helping scientists understand how environmental factors may work within the constraints of genetics to either protect or predispose to disease.  

Three Primary Genetic Theories of Aging

As noted above, there is a significant amount of evidence that looks at the importance of genes in expected survival. When looking at genetic theories, these are broken down into three primary schools of thought.

• The first theory claims that aging is related to mutations that are related to long-term survival and that aging is related to the accumulation of genetic mutations that are not repaired.
• Another theory is that aging is related to the late effects of certain genes, and is referred to as pleiotropic antagonism.
• Yet another theory, suggested based on survival in opossums, is that an environment that poses few hazards to interfere with life expectancy would result in an increase in members who have mutations that slow down the aging process.

Evidence Behind the Theory

There are several avenues of evidence that support a genetic theory of aging, at least in part.

Perhaps the strongest evidence in support of the genetic theory is the considerable species-specific differences in maximal survival, with some species (such as butterflies) having very short lifespans, and others, such as elephants and whales, being similar to ours. Within a single species, survival is similar, but survival can be very different between two species that are otherwise similar in size.

Twins studies also support a genetic component, as identical twins (monozygotic twins) are much more similar in terms of life expectancy than are non-identical or dizygotic twins. Evaluating identical twins who have been raised together and contrasting this with identical twins who are raised apart can help to separate out behavior factors such as diet and other lifestyle habits as a cause of family trends in longevity.

Further evidence on a broad scale has been found by looking at the effect of genetic mutations in other animals. In some worms as well as some mice, a single gene mutation may lengthen survival by over 50 percent.

In addition, we are finding evidence for some of the specific mechanisms involved in the genetic theory. Direct measurements of telomere length have shown that telomeres are vulnerable to genetic factors that can speed up the rate of aging.

Evidence Against Genetic Theories of Aging

One of the stronger arguments against a genetic theory of aging or a "programmed lifespan" comes from an evolutionary perspective. Why would there be a specified lifespan beyond reproduction? In other words, what "purpose" is there for life after a person has reproduced and been alive long enough to raise their progeny to adulthood?

It's also clear from what we know about lifestyle and disease that there are many other factors in aging. Identical twins may have very different lifespans depending on their exposures, their lifestyle factors (such as smoking) and physical activity patterns.

The Bottom Line

It's been estimated that genes can explain a maximum of 35 percent of lifespan, but there is still more we do not understand about aging than which we do understand.   Overall, it's likely that aging is a multifactorial process, meaning that it is probably a combination of several of the theories. It's also important to note that the theories discussed here are not mutually exclusive. The concept of epigenetics, or whether or not a gene that is present is "expressed" can further muddy our understanding.

In addition to genetics, there are other determinants of aging such as our behaviors, exposures, and just plain luck. You are not doomed if your family members tend to die young, and you can't ignore your health even if your family members tend to live long.

What Can You Do to Reduce the "Genetic" Aging of Your Cells?

We are taught to eat a healthy diet and be active and these lifestyle factors are likely just as important no matter how much our genetics are involved in aging. The same practices which seem to keep the organs and tissues of our bodies healthy may also keep our genes and chromosomes healthy.

Regardless of the particular causes of aging, it can make a difference to:

• Exercise - Studies have found that physical activity not only helps your heart and lung function well, but exercise lengthens telomeres.  
• Eat a healthy diet - A diet high in fruits and vegetables is associated with greater telomerase activity (in effect, less shortening of the telomeres in your cells). A diet high in omega-3-fatty acids is associated with longer telomeres but a diet high in omega-6-fatty acids is the opposite and associated with shorter telomeres. In addition, soda pop intake is linked with shorter telomeres. Reservatrol, the ingredient responsible for the excitement over drinking red wine (but also found in non-alcoholic red grape juice) appears to activate the longevity protein SIRT
• Reduce stress  
• Avoid carcinogens
• Maintain a healthy weight - Not only is obesity linked with some of the genetic mechanisms associated with aging noted above (such as increased shortening of telomeres), but repeated studies have found longevity benefits associated with caloric restriction.   The first principle in the cancer prevention lifestyle put forth by the American Institute for Research on Cancer—be as lean as possible without being underweight—might play a role in longevity as well as cancer prevention and the prevention of cancer recurrence.

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By Mark Stibich, PhD Mark Stibich, PhD, FIDSA, is a behavior change expert with experience helping individuals make lasting lifestyle improvements.

Rethinking ageing: introduction

• Introduction
• Published: 06 August 2021
• Volume 43 , article number  95 , ( 2021 )

Cite this article

• Alessandro Blasimme 1 ,
• Giovanni Boniolo 2 &
• Marco J. Nathan 3  

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While philosophical discussions about the nature of human ageing have never been settled, they acquire new significance in the contemporary milieu . This should be unsurprising, given the rapidly evolving age-structure of our society. According to demographic data, human populations are getting older, especially in the Western hemisphere but, generally, as a world-wide trend ( https://ourworldindata.org/age-structure ). The global percentage of senior citizens is rapidly and consistently increasing. This has raised awareness of the dynamic nature of the ageing process, as well as the diverse ways in which ageing affects people differently, because of biological factors as well as cultural and social determinants.

In recent years, philosophy has started to pay renewed attention to the conceptual and social implications of ageing, especially as they emerged from vivid debates in gerontology and geriatrics. Prominent figures from practical philosophy, in particular from ethics and bioethics, have animated a debate in the so-called philosophy of ageing – often in dialogue with psychiatrist and gerontologists (Scarre, 2016 ). Philosophers of science have had a considerably more marginal role in this domain of scholarship. This collection thus aims to reflect and, at the same time, expand the paradigm of the philosophy of ageing, giving due relevance to both its socio-ethical and epistemological implications.

1 Background

All humans experience the process of getting older, one day after another. Nevertheless, the passing of time per se is not a sufficient condition for ageing . It is only after a certain point in an individual’s life that talking about “ageing” proper seems appropriate. For an adolescent, the passing of time does not bear any mark of ageing. Youngsters may be well aware that, as time goes by, there is less for them to live. But in the early phases of a person’s life, referring to the passage of time as “ageing” does not sound quite right. The physical, psychological, and medical characteristics that are generally linked to ageing have yet to appear.

While ageing is a familiar concept of ordinary use, it is hard to characterize precisely, and not only from a philosophical point of view. Many other disciplines struggle to provide what may be considered a minimal set of typical features or hallmarks of ageing, let alone a general consensus, even if several attempts have been proposed(for a review, Lemoine, 2020 ).

Different theories and definitions of ageing have been debated for decades, as witnessed by the success enjoyed, since the late Thirties, by a scholarly genre concerned with the systematic collection of oft-conflicting accounts of ageing from a variety of disciplinary perspectives. In particular, one should mention biogerontology, that studies ageing in relation to structural damage, functional decline, depletion, and other phenotypic changes; social gerontology, dealing with the social impact of ageing; physiology, which analyses changes occurring in all organic systems; psychology, that is interested in natural or pathological cognitive decline (Cowdry, 1939 ; Burgess, 1960 ; Tibbitts, 1960 ; Birren & Bengtson, 1988 ; Weinert & Timiras, 2003 ; Johnson et al., 2005 ; Bengtson & Settersten 2016 ; Pickard, 2016 ).

Decades of theoretical studies, alongside a growing body of empirical evidence, have established that the “ageing phenotype” is the result of various concomitant forces – cultural and social, as much as biological. Therefore, biological essentialism, which defines ageing in terms of necessary and sufficient physiological properties, does not seem a viable option. As we all know from direct experience, some people acquire age-related features earlier than others. Others cope better with the effects of ageing and remain youthful until later in life. These differences may depend on a variety of factors, ranging from individual predispositions to environmental conditions, from socio-economic status to the effects of social and even medical attitudes towards given age groups. Paradoxically, however, even as we are discussing the limits of an essentialist view, we can hardly avoid speaking in terms of “life-stages,” as if such stages inevitably belonged to human life as natural kinds.

While there is no consensus as to the defining characteristics of ageing, we can observe some relative stability in the way different cultures conceive of human life as the succession of different age-dependent stages spanning youth, adulthood and seniority. Throughout history, there have been many attempts to systematize the periods of life. Interestingly, many of them focus on the number seven, a number that early Christian theologians considered significant, as it symbolized completeness. Consider, for instance, the influential Medieval saying: Septem etates homini. The human lifespan was divided into seven stages: “infantia” up to 7 years of age; “pueritia” up to 15; “adolescencia” up to 25; “Juventus” up to 35; “virilitas” up to 50; “senectus” up 70; “decrepitas,” or “gravitas” beyond 70. Setting rhetorical effects aside, the subdivision of the human lifespan into three (another significant number in the history of Christianity), seven or, for that matter, any specific number of stages, does not lend much support to a realistic understanding of ageing. In short, trying to spell out exactly when, over the course of a human life, the passing of time can appropriately be called “ageing” leads us to the heart of philosophically complex matters surrounding the meaning, use, phenomenology, epistemology and ethics of human ageing (Scarre, 2016 ).

Philosophers have been involved in such disputes for thousands of years. Aristotle’s view of ageing as a state of decline caused by a progressive, time-dependent cooling of the body causing a deterioration of character illustrates how evaluative considerations and scientific explanations may often overlap. Aristotle’s general approach to ageing remained popular for centuries. Traces can be found in the writings of Galen. Even thinkers like Plato, Cicero and Seneca, who had a more positive attitude towards ageing as bringing about wisdom and a more thoughtful demeanour, linked such features to physical decline as a state that would favour the exercise of those virtues.

As Plato, Cicero, and Seneca remind us, ageing also possesses positive connotations, such as wisdom, knowledge, or experience. Most effects, however, are less desirable, such as undergoing some degree of decline in physical vigour, health, or personal disposition. This is especially true of frequently stigmatized characteristics associated with age-related decline, such as impaired physical autonomy and cognitive function.

2 The collection

Any philosophical investigation of the conceptual hallmarks of ageing is further complicated by the observation that all the theoretical accounts of ageing are inevitably interwoven with ethical assumptions about functional fitness, as well as normative judgments concerning the desirability of age-related states. As previously noted, while everyone is familiar with ageing and its consequences, compiling a comprehensive list of the characteristics that distinguish ageing from the mere passage of time is a strikingly complex and controversial endeavour. Trying to examine conceptual and ethical dimensions of ageing in isolation would thus fail to do justice to the philosophical complexity of the topic. With this premise in mind, we have invited both philosophers of science and ethicists to contribute to this topical collection.

From an ontological standpoint, making sense of the concept of ageing raises numerous philosophical challenges. First of all, many discussions of ageing rest on the unchecked intuition that ageing is some sort of natural kind. Such intuition presupposes that breaking down the human lifespan into distinct phases reflects the structure of the natural world and tells us something objective about our life trajectory independently of our way of conceptualizing it. But, as observed, this is controversial. To what extent does this assumption withhold serious scrutiny?

Such metaphysical issues, in turn, bear on traditional ethical and social discussions related to age and ageing. For instance, the ways in which evolutionary, biological, and social determinants of ageing stand in relation to one another determine whether or not certain phenotypic manifestations of ageing should be considered as diseases – an important issue with obvious ethical, as well as medical, implications.

The goal of this topical collection is to present and discuss conceptual questions revolving around ageing and to place them in a richer epistemic context. Specifically, the essays collected here represent the efforts of a diverse group of scholars providing a fresh perspective on the meaning of ageing, in light of contemporary scientific and socio-cultural insights. This ecumenical perspective involves putting the philosophy of science and, in particular, a philosophy of the life sciences at the centre of the stage and using it as a springboard to touch upon social and normative issues. On the one hand, philosophers of science must be acutely aware of how values pervade the scientific discourse about ageing. On the other hand, ethicists and bioethicists must factor in the momentous advances in biology and medicine that have taken place over the last few decades. This is the ambitious synergy that we must aspire to, and the essays collected here set a very high bar. Incidentally, this admittedly requires a broad interpretation of philosophy of science. This could not be otherwise, given our focus on an interdisciplinary topic like ageing.

What ties this topical collection together, however, is not merely the need to shed conceptual clarity onto such an intricate matter. Rather, the overarching goal of the essays collected here is to focus on specific aspects of ageing where conceptual analysis can make a difference into the way people conceive of ageing and deal with it in practical terms. Such pragmatic orientation runs through all the essays. For instance, reflecting on the extent to which age-related cognitive decline affects personal identity (see Boniolo in this TC) has implications for the moral agency of people affected by various forms of cognitive impairment. Along similar lines, showing how the process of ageing can be understood as the manifestation of a plastic phenotype (see Blasimme and Sholl in this TC) has crucial implications for public health priorities and strategies to cope with rapidly ageing populations worldwide (see Garson, Nathan, Green & Hillersdal, and Maung in this TC).

On the other hand, addressing ethical and structural aspects of ageing, the desirability of longevity and the use of digital technologies for elder care (see Gullette, Wareham and Shicktanz in this TC) cannot be separated from background assumptions about what ageing is and whether it can be understood in terms of deficits in relation to an allegedly fully functional phase of human life (see Jecker in this TC).

Another distinctive feature of this topical collection has to do with methodological breadth. Alongside traditional conceptual analysis in the tradition of Audi, 1983 and Iversen, 2009 , these essays employ a variety of philosophical techniques and social science tools. Examples include the use of ethnographic data (Green in this TC), historical analysis (Blasimme in this TC), social critique (Gullette in this TC) and normative analysis (Schiktanz and Jecker in this TC). Such methodologies, while rooted in different disciplinary traditions, all cater to the distinctively philosophical aim of the collection, that is, to clarify key conceptual quandaries about ageing that have practical implications for the way ageing is understood and dealt with.

Giovanni Boniolo’s “Demented Patients and the Quandaries of Identity: Setting the Problem, Advancing a Proposal” focuses on the substantial effects of dementia – decline of memory, attention, learning, language, perception, and social cognition strongly associated with ageing – on the concepts of the self , identity and personhood (Boniolo, 2021 ). After clarifying the meaning of these key terms, Boniolo advances an empirical thesis concerning personal identity, based on the notion of the whole phenotype account. He defends the claim that patients with dementia are able to maintain their whole phenotype identity. Boniolo concludes by drawing some implications for the capacity of patients with dementia to make moral decisions.

In a paper entitled “Ageing and the Goal of Evolution,” Justin Garson proposes to examine a widespread metaphor, according to which the goal or purpose of natural selection is to perpetuate the species (Garson, 2021 ). Consequently, individuals have the task of breeding and, in some species, raise the brood to maturity. The article begins by illustrating the pervasiveness of this image, showing that this is indeed a metaphor, as opposed to a claim that should be understood literally, and outlining its implications for ageing, namely, the declining force of natural selection with age. At the same time, Garson suggests, this metaphor should be discarded, on the grounds that it distorts our understanding of the evolution of ageing.

Marco J. Nathan’s essay “Does Anybody Know What Time It Is? From Biological Age to Biological Time” explores the prospects of developing a truly biological conception of age (Nathan, 2021 ). Nathan’s point of departure is the celebrated 1922 debate between Albert Einstein and Henri Bergson, where Einstein famously proclaimed that the time of the philosopher does not exist. Einstein’s dictum has been metabolized across the natural sciences, which typically presuppose, more or less explicitly, the existence of a single, univocal, temporal dimension, ultimately determined by physics. Nathan argues that the standard practice of assessing the ageing of organisms against the backdrop of a physical conception of time is problematic. This becomes especially evident in light of recent discoveries of various levels of senescence underlying the ageing of individual organisms—a phenomenon known as “age mosaicism.” The bottom line of these considerations, Nathan concludes, is that the study of ageing requires a truly biological conception of age, as opposed to a physical one.

Hane Maung’s article, “What’s My Age Again? Age Categories as Interactive Kinds” explores the ontological status of age classification (Maung, 2021 ). While age categories, such as “young adulthood,” “middle adulthood,” and “older adulthood” intuitively seem to qualify as natural kinds, this is hard to reconcile with the historical instability of these categories. The properties allegedly captured by age categories are deeply affected by medical and cultural developments. In addition, the very act of classifying people in specific age-related categories can trigger changes in their behaviour which, in turn, affects the properties that we are trying to capture. Maung suggests here that age categories are best understood as interactive kinds that are influenced in dynamic ways by looping effects and explores some implications of this proposal.

In their article “Ageing Biomarkers and the Measurement of Health and Risk,” Sara Green and Line Hillersdal skilfully blend philosophical analysis and ethnographic fieldwork to explore both challenges and opportunities of measuring and managing ageing through bodily signs that are not straightforwardly linked to symptomatic disease (Green & Hillersdal, 2021 ). More specifically, this paper documents how the aim to measure and quantify ageing, more precisely, as risk is confronted with both experimental and conceptual challenges. They conclude by highlighting that the reframing of ageing qua risk has social and ethical implications, as it is generative of normative notions of what constitutes successful ageing and good citizenship.

In his article “The Plasticity of Ageing and the rediscovery of ground-state prevention” Alessandro Blasimme explores how the ageing-phenotype grew as a proper object of medical intervention since the birth of modern geriatric medicine in the mid-twentieth century until the emergence of novel biomedical insights, in the last decade (Blasimme, 2021 ). The article also shows that a new understanding of prevention is associated to seeing ageing as a plastic phenotype – one that bears resemblance with long-held medical ideals about the preservation of health throughout one’s life.

Along similar lines, Jonathan Sholl’s article, “Can Ageing Research Generate a Theory of Health?” explores the prospects of developing a general theory of health (Sholl, 2021 ). He begins with some generalizations about “health” implicit within research on robust scientific descriptions of ageing and its modulators. By extracting, explicating, and evaluating one potential construct of health in these models, Sholl proposes a theory of health based on the trajectory of optimized phenotypic trade-offs.

Christopher Wareham, in his paper “Between Hoping to Die and Longing to Live Longer”, offers a meticulous ethical analysis on the desirability of longevity (Wareham, 2021 ). Wareham constructs his analysis of this classical philosophical theme around contemporary debates on the morality of intentionally setting a limit to one’s life span. He argues against the idea that aiming to live beyond a certain old age is not worth hoping for, he shows that contemplating death may have an instrumental value in shaping one’s purposes and motivating one to act towards them.

In her essay titled “Ageism in State Power and Literary Culture: Preparing the Way for the COVID-Era Eldercide in the United States” age-studies scholar Margaret Morganroth Gullette explores the cultural underpinnings of derogatory conceptions of old age and their practical consequences in the context of the SARS-CoV-2 pandemic. Her article illustrates deep-seeded ageist prejudices underpinning discourses about old age – including the philosophical discussions on the limits of longevity covered by Wareham – and shows how they explain the appalling toll of avoidable deaths that occurred among elders, especially in long-term care facilities.

Silke Schiktanz and Mark Schweda, in their paper “Ageing 4.0? – Rethinking the Ethical Framing of Technology-assisted Eldercare” present a normative analysis of novel assistive technologies. In particular, they focus on self-tracking and monitoring technologies, including those relying on digital platforms and employing smart approaches and artificial intelligence. This analysis shows how the use of such technologies has ethical implications regarding the autonomy of the assisted person, her capacity for self-determination, her privacy, well-being and her right to equitable and fair access to eldercare.

Nancy Jecker’ s “The Time of One's Life: Views of Ageing and Age Group Justice” tackles issues of intergenerational justice in light of different possible accounts of ageing and their normative implications (Jecker, 2021 ). Jecker illustrates how what she calls a midlife bias – that is, the tendency to apply values central for people during midlife to all life stages – sustains views of ageing that neglect the biographical unity of human life in favour of a snapshot view of the midlife self. Such different images of human life support different understandings of age group justice as either interpersonal or first-person problems. Instead of considering these approaches as mutually exclusive, Jecker suggests that they can inform different but equally important practical and normative purposes.

In conclusion, while the import of ageing as a biological and social phenomenon is widely recognized in the biomedical science, it has received surprisingly little attention in the philosophy of the life sciences and cognate fields. The goal of this edited collection is to begin filling in this gap, by discussing the metaphysical, epistemological, and ethical implications of ageing, broadly construed, as well as the philosophical implications of extant biomedical practices.

These essays are the outcome of a workshop that was held on December 12–13, 2019 at the Civitas Vitae Research Centre of the Fondazione OIC Onlus in Padova, Italy, in partnership with the Health Ethics and Policy Lab of the Swiss Federal Institute of Technology—ETH Zurich.

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Acknowledgements

The authors are grateful to Sabina Leonelli and Mallory Hrehor for constructive comments on this paper, as well as to the Fondazione OIC ( Civitas Vitae Research Centre ) and ETH Zurich for supporting this project. AB would like to acknowledge the European Commission and the Swiss National Science Foundation for their support to the ERA-NET Neuron project BEAD “Optimizing the aging Brain? Situating Ethical Aspects of Dementia Prevention”.

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Aged people usually undergo pangs of loneliness and need companionship. the pessimistic approach they develop towards life can be shunned only if we provide them with abundant love, care, importance and empathy. they expect their children to sit calmly and talk to them about the happenings of their lives and to take their suggestions for making significant decisions. their lost vitality can thus be easily rejuvenated. this happiness will encourage them to live life enthusiastically. (a model answer has been provided for students' reference. it is strongly recommended that students prepare the answer on their own.).

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Science is making anti-aging progress. But do we want to live forever?

Nobel laureate details new book, which surveys research, touches on larger philosophical questions

Anne J. Manning

Harvard Staff Writer

Mayflies live for only a day. Galapagos tortoises can reach up to age 170. The Greenland shark holds the world record at over 400 years of life. 

Venki Ramakrishnan, Nobel laureate and author of the newly released “ Why We Die: The New Science of Aging and the Quest for Immortality ,” opened his packed Harvard Science Book Talk last week by noting the vast variabilities of lifespans across the natural world. Death is certain, so far as we know. But there’s no physical or chemical law that says it must happen at a fixed time, which raises other, more philosophical issues.

The “why” behind these enormous swings, and the quest to harness longevity for humans, have driven fevered attempts (and billions of dollars in research spending) to slow or stop aging. Ramakrishnan’s book is a dispassionate journey through current scientific understanding of aging and death, which basically comes down to an accumulation of chemical damage to molecules and cells.

“The question is whether we can tackle aging processes, while still keeping us who we are as humans,” said Ramakrishnan during his conversation with Antonio Regalado, a writer for the MIT Technology Review. “And whether we can do that in a safe and effective way.”

Even if immortality — or just living for a very, very long time — were theoretically possible through science, should we pursue it? Ramakrishnan likened the question to other moral ponderings.

“There’s no physical or chemical law that says we can’t colonize other galaxies, or outer space, or even Mars,” he said. “I would put it in that same category. And it would require huge breakthroughs, which we haven’t made yet.”

In fact, we’re a lot closer to big breakthroughs when it comes to chasing immortality. Ramakrishnan noted the field is moving so fast that a book like his can capture but a snippet. He then took the audience on a brief tour of some of the major directions of aging research. And much of it, he said, started in unexpected places.

Take rapamycin, a drug first isolated in the 1960s from a bacterium on Easter Island found to have antifungal, immunosuppressant, and anticancer properties. Rapamycin targets the TOR pathway, a large molecular signaling cascade within cells that regulates many functions fundamental to life. Rapamycin has garnered renewed attention for its potential to reverse the aging process by targeting cellular signaling associated with physiological changes and diseases in older adults.

Other directions include mimicking the anti-aging effects of caloric restriction shown in mice, as well as one particularly exciting area called cellular reprogramming. That means taking fully developed cells and essentially turning back the clock on their development.

The most famous foundational experiment in this area was by Kyoto University scientist and Nobel laureate Shinya Yamanaka, who showed that just four transcription factors could revert an adult cell all the way back to a pluripotent stem cell, creating what are now known as induced pluripotent stem cells.

Ramakrishnan , a scientist at England’s MRC Laboratory of Molecular Biology, won the 2009 Nobel Prize in chemistry for uncovering the structure of the ribosome. He said he felt qualified to write the book because he has “no skin in the game” of aging research. As a molecular biologist who has studied fundamental processes of how cells make proteins, he had connections in the field but wasn’t too close to any of it.

While researching the book, he took pains to avoid interviewing scientists with commercial ventures tied to aging.

The potential for conflicts of interest abound.

The world has seen an explosion in aging research in recent decades, with billions of dollars spent by government agencies and private companies . And the consumer market for products is forecast to hit $93 billion by 2027 .

As a result, false or exaggerated claims by companies promising longer life are currently on the rise, Ramakrishnan noted. He shared one example: Supplements designed to lengthen a person’s telomeres, or genetic segments that shrink with age, are available on Amazon.

“Of course, these are not FDA approved. There are no clinical trials, and it’s not clear what their basis is,” he said.

But still there appears to be some demand.

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Science is making anti-aging progress. But do we want to live forever?

by Anne J. Manning, Harvard Gazette

Mayflies live for only a day. Galapagos tortoises can reach up to age 170. The Greenland shark holds the world record at over 400 years of life.

Venki Ramakrishnan, Nobel laureate and author of the newly released book "Why We Die: The New Science of Aging and the Quest for Immortality," opened his packed Harvard Science Book Talk last week by noting the vast variabilities of lifespans across the natural world .

Death is certain, so far as we know. But there's no physical or chemical law that says it must happen at a fixed time, which raises other, more philosophical issues.

The "why" behind these enormous swings, and the quest to harness longevity for humans, have driven fevered attempts (and billions of dollars in research spending) to slow or stop aging. Ramakrishnan's book is a dispassionate journey through current scientific understanding of aging and death, which basically comes down to an accumulation of chemical damage to molecules and cells .

"The question is whether we can tackle aging processes, while still keeping us who we are as humans," said Ramakrishnan during his conversation with Antonio Regalado, a writer for the MIT Technology Review. "And whether we can do that in a safe and effective way."

Even if immortality—or just living for a very, very long time—were theoretically possible through science, should we pursue it? Ramakrishnan likened the question to other moral ponderings.

"There's no physical or chemical law that says we can't colonize other galaxies, or outer space, or even Mars," he said. "I would put it in that same category. And it would require huge breakthroughs, which we haven't made yet."

In fact, we're a lot closer to big breakthroughs when it comes to chasing immortality. Ramakrishnan noted the field is moving so fast that a book like his can capture but a snippet. He then took the audience on a brief tour of some of the major directions of aging research. And much of it, he said, started in unexpected places.

Take rapamycin, a drug first isolated in the 1960s from a bacterium on Easter Island found to have antifungal, immunosuppressant, and anticancer properties. Rapamycin targets the TOR pathway, a large molecular signaling cascade within cells that regulates many functions fundamental to life. Rapamycin has garnered renewed attention for its potential to reverse the aging process by targeting cellular signaling associated with physiological changes and diseases in older adults.

Other directions include mimicking the anti-aging effects of caloric restriction shown in mice, as well as one particularly exciting area called cellular reprogramming. That means taking fully developed cells and essentially turning back the clock on their development.

The most famous foundational experiment in this area was by Kyoto University scientist and Nobel laureate Shinya Yamanaka, who showed that just four transcription factors could revert an adult cell all the way back to a pluripotent stem cell, creating what are now known as induced pluripotent stem cells.

Ramakrishnan, a scientist at England's MRC Laboratory of Molecular Biology, won the 2009 Nobel Prize in chemistry for uncovering the structure of the ribosome. He said he felt qualified to write the book because he has "no skin in the game" of aging research. As a molecular biologist who has studied fundamental processes of how cells make proteins, he had connections in the field but wasn't too close to any of it.

While researching the book, he took pains to avoid interviewing scientists with commercial ventures tied to aging.

The potential for conflicts of interest abound.

The world has seen an explosion in aging research in recent decades, with billions of dollars spent by government agencies and private companies. And the consumer market for products is forecast to hit $93 billion by 2027.

As a result, false or exaggerated claims by companies promising longer life are currently on the rise, Ramakrishnan noted. He shared one example: Supplements designed to lengthen a person's telomeres, or genetic segments that shrink with age, are available on Amazon.

"Of course, these are not FDA approved. There are no clinical trials , and it's not clear what their basis is," he said.

But still there appears to be some demand.

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Ageism and Psychological Well-Being Among Older Adults: A Systematic Review

1 Department of Social Work, George Mason University, Fairfax, VA, USA

2 National Rehabilitation Research and Training (RRT) Center on Family Support, University of Pittsburgh, Pittsburgh, PA, USA

Ageism may have harmful effects on the psychological well-being of older adults, leading to mental health issues, such as depression and anxiety. However, there are insufficient data to establish this hypothesis, and most work on the subject has appeared only in the form of conceptual or theoretical papers. This study reviewed quantitative studies of the relationship between ageism and psychological well-being of older adults. We conducted a comprehensive review using searches of academic databases, the grey literature, hand searches, and reference mining. A total of thirteen articles were selected using the inclusion criteria. All the reviewed studies showed a negative association between ageism and the psychological well-being of older adults. The study confirmed a negative association between ageism and older adults’ psychological well-being, finding that older adults with a high level of psychological well-being may be less negatively affected by ageism, especially those who were proud of their age group, experienced less negative emotions, were more optimistic about aging and their future, were more self-confident about their bodies, and were flexible in setting goals. The identified mediators of the association can inform intervention development to the effects of ageism and improve older adults’ psychological well-being.

Introduction

Growing older involves gaining maturity and becoming a more responsible and respectful adult. The process of aging can be viewed unfavorably by some people, who view it pessimistically, and this reduces the pleasure they may have gained from their own growth ( Kang, 2020 ). Aging is often considered to be a challenging process, during which individuals lose their confidence and experience a loss of productivity ( Schafer & Shippee, 2009 ). Significant declines in social and cultural status have been observed in older adults over the past century as a result of industrialization and modernization ( Aboderin, 2004 ; Nelson, 2005 ). The industrial age and technological advancements have increased the need for people to work efficiently and quickly to remain competitive ( Tuomi et al., 1997 ). These changes have had the effect of decreasing the need for and visibility of older adults’ activities ( Solem, 2005 ).

A growing body of research has observed an increase in negative attitudes toward older individuals over the years ( Nelson, 2005 ; Scharlach et al., 2000 ). Several studies have shown that members of the younger generations now exhibit more negative views and attitudes toward older adults than was previously the case ( North & Fiske, 2012 ). Negative beliefs and attitudes towards older adults are increasingly prevalent, which may add to the barriers that older adults face when seeking employment ( Skirbekk, 2004 ). Consequently, older adults are often considered to be merely passive recipients of welfare, and they may even be accused of being a burden to younger generations ( Hudson, 2012 ). The belief that older adults are less valuable or of no interest to society may contribute to ageism.

Ageism is stereotyping, prejudice, and discriminatory actions or attitudes based on chronological age ( Iversen et al., 2009 ). Ageism, therefore, can be operationalized as stereotypes, prejudices, and discrimination, and each of those components, individually, can be seen as cognitive, affective, and behavioral ( Iversen et al., 2009 ). Consequently, age stereotypes are fixed beliefs that overgeneralize the characteristics, attributes, and behaviors held in common by a particular group ( Whitley & Kite, 2006 ). Age stereotypes can contribute to assumptions about a person’s physical and mental capabilities, social skills, political and religious beliefs, and other traits based on their age ( World Health Organization, 2021 ). A prejudice is a negative or positive emotional reaction to a person based on their perceived affiliation with a particular group ( World Health Organization, 2021 ). Age prejudice is one of the most socially vocalized and institutionalized prejudices in many segments of society, and it is disregarded in numerous aspects of social life ( Nelson, 2005 ). A discriminatory act is characterized primarily by distorted behavior that treats individuals in a non-constructive manner ( Dovidio et al., 2011 ). Age discrimination is behavior directed at people based on their age, including actions, practices, and policies ( World Health Organization, 2021 ).

Ageism is a very serious issue. While it can theoretically be directed toward any age group, the vast majority of studies focus on older adults or late adolescents ( Nelson, 2005 ). Although ageism can be shown in terms of positive stereotypes or attitudes, it is most closely associated with negative stereotypes or attitudes ( Palmore, 1999 ). Ageism can manifest in two main ways: implicitly, through unconscious thoughts, feelings, and behaviors, or explicitly, through intentional actions or verbal expressions triggered by conscious awareness ( Iversen et al., 2009 ). Furthermore, ageism is not restricted to directed toward others but can also be self-directed ( Ayalon & Tesch-römer, 2017 ). Exposure to ageism over time can result in the internalization of ageist attitudes and stereotypes, as described by Levy (2009) in stereotype embodiment theory. Many older adults tend to internalize the negative stereotypes of ageism that continue to be perpetuated throughout society today and tend to confine themselves to age-related stereotypes, becoming weak, unhealthy, and even less able to accept new learning opportunities ( Streb et al., 2008 ).

Internalized age stereotypes may lead to low levels of self-esteem and self-confidence ( Orth et al., 2010 ), and it may affect older adults’ health negatively ( Emile et al., 2014 ), especially with regard to their mental health and well-being ( Bryant et al., 2012 ). An individual who believes that they are too old may be more susceptible to the negative consequences of ageism, which may include decreased self-efficacy and increased negative emotions ( Eibach et al., 2010 ). The converse may also be true, as positive perceptions and attitudes on aging may have beneficial effects on psychological well-being ( Bryant et al., 2012 ). Older adults who have experienced discrimination based upon their chronological age may be more exposed to stressors ( Snape & Redman, 2003 ) and depression ( Tougas et al., 2004 ), which are detrimental to their mental health ( Pascoe & Richman, 2009 ).

Ageism is increasingly recognized as a risk factor associated with increased stress, anxiety, depression, and lowered life satisfaction ( Ayalon et al., 2019 ). However, articles on ageism generally take the form of conceptual or theoretical papers, and they tend to center on identifying the causes and consequences of ageism ( Iversen et al., 2009 ). More empirical studies are needed to investigate the harm that ageism can cause to the psychological well-being of older adults. Our review examined this relationship by synthesizing the results of several studies identified in a thorough systematic search.

Purpose of the Review

This systematic review examines how the experience of ageism experience among older adults influences their psychological well-being. This study also seeks insight into successful aging by identifying factors that mediate or moderate the relationship of ageism to psychological well-being. Our overarching goal is to mitigate or eliminate the adverse effects of ageism, especially on the psychological well-being of older adults. Using a systematic review method allows the researcher to comprehensively identify relevant literature through transparent and rigorous processes ( Littell et al., 2008 ). Several systematic reviews have examined ageism and its effects on older adults: these include assessments of how stereotypes of aging affect memory and cognitive performance ( Lamont et al., 2015 ), ageism’s broad effects, and theories that explain ageism ( North & Fiske, 2012 ). However, no research has hitherto examined the direct effects of ageism on older adults’ psychological well-being.

A new paradigm for understanding the aging society is necessary in the face of a rapidly expanding population of older adults to assess these developments in a long-term perspective. The study of ageism can be a key foundational resource for older adults. Unbiased summaries of quantitative outcome studies from our systematic review may help to develop an understanding of the potential risks of ageism on psychological well-being. Furthermore, the mediators and moderators identified between ageism and the psychological well-being of older adults will support future policy and practices.

We aimed to locate all empirical evidence that examined the relationship between ageism and older adults’ psychological well-being through a comprehensive and unbiased search. The systematic review methodology was guided by two sources: Systematic Reviews from the Centre for Reviews and Dissemination (2009) and Systematic Reviews and Meta-Analysis from Littell et al. (2008) . We also followed the guidelines from a review protocol, the PRISMA 2020 statement (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) developed by Page et al. (2021) , to verify the validity of the steps involved in the systematic review. PRISMA is a set of standards that includes a 27-item checklist and a four-phase flow diagram describing how systematic reviews should be reported ( Page et al., 2021 ). The completed PRISMA checklist was included in Appendix B . A critical appraisal checklist for analytical cross-sectional studies developed by the Joanna Briggs Institute (JBI) was used to assess the methodological quality of the reviewed studies ( Moola et al., 2020 ). Additionally, we reported our results using Pleasant et al.'s (2020) study as a guide ( Pleasant et al., 2020 ). Our first step was to develop a search strategy to guide a thorough but rigorous systematic search by refining our research question. We also articulated and tested our complete set of search terms to decrease our chances of missing relevant literature. A number of inclusion and exclusion criteria were set to prevent bias in the selection process. We used a wide range of sources for our review, including several electronic databases, grey literature, hand searches, and reference mining.

Criteria for Considering Studies for the Review

Studies included in this review focused on the psychological well-being of older adults who have experienced discrimination based on their age. Studies had to meet several criteria to be eligible for inclusion in this review. For ensuring comprehensive and unbiased literature searches, the PICOS (Population, Intervention, Comparison, Outcomes, and Study design) framework was used to formulate literature search strategies ( Table 1 ). The population of interest for the systematic review was older adults aged 60 and above. Our rationale behind selecting this age range was based on retirement age. The retirement age varies around the world, and it is expected to increase along with increased life expectancy ( Forman & Chen, 2008 ). We adopted an average retirement age range from the Organization for Economic Co-operation and Development’s (OECD) countries from statistics on the average retirement age ( OECD, 2015 ). The normal retirement age of OECD countries in 2014 ranges from 60 (Luxembourg) to 67 (Iceland) ( OECD, 2015 ).

PICOS Framework for Systematic Review.

The review included studies that measured ageism or attitudes towards older adults. Ageism can be direct or indirect, and it tends to be reproduced and unconsciously reflected in social or cultural spheres ( Iversen et al., 2009 ). While ageism toward older adults might also be demonstrated in a positive stereotype or attitudes toward them ( Palmore, 1999 ), ageism in this study was confined to only negative attitudes and feelings. Furthermore, we included studies on self-directed ageism, which refers to ageism directed at oneself, in order to examine how internalized age stereotypes affect older adults’ psychological well-being. The large number of words associated with ageism prompted us to choose broad and general search terms in order to avoid the omission of relevant articles and to identify all potentially relevant studies.

In this study, the psychological well-being of older adults was the outcome of interest. Psychological well-being is a multi-dimensional concept determined by multiple components and factors ( Kim et al., 2017 ). We adopted a broader definition of psychological well-being as suggested by Diener et al. (2017) . They conceptualized psychological well-being as an all-inclusive term that includes desirable psychological characteristics as well as subjective well-being; that is, the subjective perception of life that an individual experiences in their environment ( Baker et al., 2005 ). Psychological well-being is a key indicator for measuring the subjective aspects of quality of life ( Baker et al., 2005 ). Further, it is an integrative construct that includes diverse affective and cognitive dimensions, such as life satisfaction, positive/negative affect, mental health, self-actualization, optimal functioning, happiness, and mood ( Levin & Chatters, 1998 ; Ryff, 1989 ). Depression, life satisfaction, stress, and other mental health behaviors were also considered in measuring psychological well-being. Study designs were limited to empirical quantitative studies that used statistical, rather than descriptive, analysis to present findings. Studies that met this population, predictor, outcome, and type of study criteria were eligible for review consideration.

To summarize, ageism literature was systematically reviewed using the following criteria: (a) focused solely on ageism without any other forms of discrimination; (b) measured ageism against older adults (60 years old and above); (c) examined the relationship between ageism and psychological well-being; (d) was written in English; and (e) used a quantitative design. Studies were excluded that (a) identified other sources of discrimination such as disability, race, sexuality, HIV, LGBTQ (lesbian, gay, bisexual, transgender, and questioning), and mental illness; (b) examined the relationship between ageism and physical health without psychological well-being; (c) used ageism as an outcome variable; and (d) used a literature review and qualitative design as the research method.

Search Strategy

To identify and determine all published research studies on ageism focusing on the influence on older adults’ psychological well-being, we conducted a comprehensive search to identify all potentially relevant literature from the inception of each index to August 31, 2019, both published and unpublished. We searched relevant resources regardless of the country of origin but only included resources written in English. In order to find all potential studies, we established four search strategies: database searches, grey literature searches, hand searches of selected journals, and reference mining. We used three bibliographic databases: ProQuest Research Library , Web of Science , and Academic Search Complete for our literature search. The search included all literature from the earliest years that the databases cover to August 31, 2019. The set of search terms included Ageism (or ageist), older adults (or aged or the elderly), and psychological (or emotional) well-being (or health or satisfaction). Various combinations of terms were tested to identify all potentially relevant studies, and our final search terms used for each database were provided in Appendix A .

To find possible unpublished literature on our topic, we visited websites of state/national government agencies, research centers, and both profit/nonprofit organizations that were most relevant to our topic and selection criteria. The grey literature sites included Cochrane Library , ProQuest Dissertations & Theses , American Psychological Association (APA) , American Society on Aging (ASA) , National Center on Elder Abuse (NCEA) , National Committee for the Prevention of Elder Abuse (NCPEA) , and The Fiske Lab. A general web search located additional studies through google and google scholar .

Four journals that were highly relevant to the search criteria were selected for a hand search to supplement unidentified literature that might have been missed through an electronic search: Ageing and Society (1981–present), Aging and Mental Health (1997–present), Gerontologist (1961–present), and Psychology and Aging (1986–present). We searched the entire contents of the four journals to find potentially eligible studies. Backward reviews through a reverse bibliographic search were also included for the hand search. Furthermore, we scanned the relevant references from articles identified through previous search methods to identify additional literature that met the search criteria.

Data Collection and Analysis Methods

We used EndNote X9, a reference managing computer program, for data collection processes, including downloading results of electronic searches, organizing downloaded references, checking duplication, and locating full texts. The data collection process started by first retrieving abstracts or titles for all resources through the search process. The second screening process involved reviewing full texts of the initially screened resources to determine if the sources were relevant by applying exclusion and inclusion criteria. For reliability of quality assessment and data extraction, all screening processes were undertaken by both the first author and the second author. Disagreements about screening and full-text retrieval decisions were discussed until reaching a consensus.

After the full-text review, final resources were selected for data extraction. The first author collected data from the final resources, and the second author checked and revised the data extraction by the first author and supplemented insufficient data, if needed. Disagreements among the two authors were again resolved by consensus to establish inter-rater reliability in the data extraction process. The data collection included (a) Study design: overarching goal, study site and control variables, (b) Methodology: type of data, data collection methods and statistical techniques, (c) Sample: random sampling, sample size, and sample characteristics (age, education level, race/ethnicity, (d) Predictor (ageism): data source, measures, tools used, information regarding the validity of tools, (e) Outcome (psychological well-being): data source, list of outcomes assessed, measures, tools used, information regarding the validity of tools, (f) Findings: the relationship between ageism and psychological well-being (statistically significant associated or not associated), and (g) Intervention: interventions between ageism and psychological well-being (statistically significant associated or not associated). Finally, to establish the study quality standards, information regarding (a) Internal validity (missing data and reliability and/or validity of variables) and (b) External validity (representative of the population) were extracted

Figure 1 illustrates the search process. The database search identified 6103 records, while additional 314 records were identified from other sources. 673 duplicates were removed from the initial sample ( n = 6417). A screening of the remaining records’ titles and abstracts ( n = 5744) was conducted to ascertain eligibility criteria, which led to the exclusion of ( n = 5447) records. All of the remaining articles ( n = 297) were evaluated by full-text review, and 284 articles were excluded for the reasons outlined in Figure 1 . Thirteen articles were ultimately selected for data extraction.

Systematic review flow diagram.

Studies’ Design and Setting

All thirteen studies examined the relationship between ageism and the psychological well-being among older adults aged 60 and above. Table 2 shows a summary of the study design and setting of thirteen studies. 38% ( n = 5/13) proposed and tested interventions that buffer the relationship between ageism and psychological well-being. 31% ( n = 4/13) adopted conceptual frameworks to explain and verify the association between ageism and psychological health. Stereotype internalization theory ( Bai et al., 2016 ), stress process model ( Kim, 2015 ), minority stress theory ( Lyons et al., 2018 ), and stereotype embodiment theory ( Zhang et al., 2019 ) were used as theoretical grounds to support the ageism and psychological health link.

Study Design and Setting.

1 IADL: Instrumental Activities of Daily Living.

38% ( n = 5/13) were conducted in the US and 46% ( n = 6/13) in Asia. There was one study conducted in Europe, and the other in Germany, Mexico, and Spain. 38% ( n = 5/13) conducted a secondary analysis of existing data, and the samples in these studies were selected through a probability sample design. 15% ( n = 2/13) were longitudinal panel research, whereas all the other studies were cross-sectional design. Except for one PhD dissertation ( Kim, 2015 ), all other studies (92%) were published in peer-reviewed journals and were published between 2004 and 2019.

Studies’ Participants

Table 3 provides a summary of the 13 studies included in this review, along with each of their participants’ characteristics. The number of participants in the studies varied considerably, from 60 in a non-random sampling setting ( Garstka et al., 2004 ) to 3991 in an RCT that drew from a nationally representative survey ( Kim, 2015 ). All of the participants in the reviewed studies were older adults aged 60 years and older. The lowest mean age was 62.49, while the highest one was 77.4. Lee and Kim (2016) and Sabik (2013) included women only, while the other studies included men and women.

Sample Characteristics.

Measurement

38% ( n = 5/13) used established scales that have been used and evaluated. Three studies used Palmore’s (1999 , 2001) ageism scale ( Kim et al., 2015 ; Lee & Kim, 2016 ; Lyons et al., 2018 ). Zhang et al. (2018) and Zhang et al. (2018) used the Image of Aging Scale developed by Levy et al.(2004) . 62% ( n = 8/13) used non-validated measures or developed their scales to measure ageism. Avidor et al. (2017) , Kim (2015) , and Shin et al. (2018) used a dichotomous variable to measure age-based discriminations. Bai et al. (2016) used a measure of perceptions of aging as a burden to examine the self-directed ageism of older adults. Fernandez-Ballesteros et al. (2017) used three questions with a 4-point Likert-type scale to measure negatively perceived age discrimination. Garstka et al. (2004) measured ageism through four different items: victims of age discrimination as an individual, age group victimized by society according to age, deprivation of opportunities, and discrimination due to old age. Siguaw et al. (2017) used four items that were developed by Garstka et al. (2004) . Sabik (2013) used five questions to assess ageism: individual/age group deprivation of opportunities, exclusion from many sectors of public life, considered to be worthless after retirement, achievements not properly appreciated because of chronological old age. All measures of ageism in the included studies provided Cronbach’s alpha, and 85% ( n = 11/13) were above .75.

Psychological Well-being

92% ( n = 11/13) used validated outcome measures to evaluate older adults’ psychological well-being. Reviewed studies measured psychological well-being with different measurement instruments such as depression, subjective well-being through life satisfaction, and mental health. The outcome variable for 54% of the studies ( n = 7/13) was depression. 38% ( n = 5/13) used the concept of subject well-being by measuring life satisfaction. Ballesteros et al.’ s (2017) study included a life satisfaction measure as a component of measuring active aging. Garstka et al. (2004) assessed self-esteem in addition to life satisfaction as outcome measures. Sabik (2013) used the 5-item Mental Health subscale from the MOS 36-Item Short-Form Health Survey, which assesses general mental health and well-being. Cronbach’s alphas of all the measures of psychological well-being in the included studies were all above. Seventy-seven except the life satisfaction measure (Cronbach’s α: 0.57) of Garstka et al. (2004) .

Relationship between Ageism and Psychological Well-being

All of the studies indicated that an increase in experiences of ageism was a statistically significant predictor of decreased psychological well-being in older adults ( Table 4 ). 62% ( n = 8/13) examined ageism as a predictor that influences the psychological well-being of older adults through the regression analysis. All regressions include many control variables such as sociodemographic, socioeconomic, and physical health status. 38% ( n = 5/13) conducted structural equation modeling tests to look at direct or indirect effects of ageism.

Summary of Results (Relationship between Ageism and Psychological Well-being).

1 T1: Time 1, 2008; T2: Time 2, 2011

2 GDS: Geriatric Depression Scale.

3 CES-D: Center for Epidemiologic Studies Depression.

4 MOS: Medical Outcomes Study.

5 SWL: The Satisfaction with Life Scale.

6 PAS: Positive Age Stereotypes.

7 NAS: Negative Age Stereotypes.

Depression was an outcome assessed in 54% ( n = 7/13). An increase in experiences or perceptions of ageism (or age discrimination) was associated with an increase in depressive symptoms as well as stress and anxiety. The study by Lyons et al. (2017) showed that ageism experience is significantly related to the prevalence of stress and anxiety disorders, as well as depression. In Lee and Kim’s (2016) study, ageism was found to affect stress directly and had an indirect effect on depression through stress. Zhang et al. (2019) indicated that negative age stereotypes were associated with higher levels of depression and loneliness and lower morale.

Life satisfaction was included as an outcome measure in 38% of the total studies ( n = 5/13). The results of these studies indicated that perceived ageism and ageism experience was negatively associated with life satisfaction. The study by Fernandez-Ballesteros et al. (2017) found that perceived ageism negatively affects active aging, which includes life satisfaction, subjective health, and self-perceptions of aging. Garstka et al. (2004) showed a direct negative effect of age discrimination on self-esteem as well as life satisfaction. Lastly, Sabik’s (2013) study indicated that perceived age discrimination is negatively associated with general mental health and well-being.

Interventions Between Ageism and Psychological Well-being

38% ( n = 5/13) proposed and tested mediating and moderating variables between ageism and older adults’ psychological well-being ( Table 5 ). Garstka et al. (2004) examined the mediating effect of age group identification, which refers to an individual’s internal perception of their own age group. It was based on the rejection–identification theory, which suggests that perceived discrimination deteriorates the psychological well-being in low-status groups, but that group identification partially alleviated this effect. Age group identification attenuated the negative effect of ageism on well-being. The total effect of ageism on the psychological well-being decreased ( β = −.36, p < .05) compared to its direct effect ( β = −.54, p < .05).

Summary of Results (Interventions between Ageism and Psychological Well-being).

1 NAS: Negative Age Stereotypes.

2 PAS: Positive Age Stereotypes.

3 FGA: Flexible Goal Adjustment.

Kim (2015) tested the mediating effects of self-perception of aging and purpose in life on the relationship between ageism and depression. The overall indirect effect of ageism on depression mediated by self-perception of aging and purpose in life was statistically significant ( β = .124, p < .001). The mediating effect of self-perception of aging ( β = .112, p < .001) was larger than that of purpose in life ( β = .012, p = .048).

Kim et al. (2015) examined the mediating effect of emotional reactions and the moderating effect of coping responses. The duration of many negative emotional reactions was examined, including being hurt, angry, frustrated, humiliated, discouraged, terrified, foolish, or ashamed. Coping responses included problem-focused responses such as formal action, confrontation, and seeking support, and emotion-focused such as passive acceptance and emotional discharge. Although the results did not confirm the moderating effect of coping responses, the effect of ageism on depression ( β = −.01, p > 0.05) was no more statistically significant after adding emotional reactions.

Sabik (2013) tested the mediating effect of body esteem on the relationship between ageism and the psychological well-being of older adults. Sabik assumed that a high level of body esteem might mediate the association between ageism and psychological well-being. The results suggested that body esteem partially mediated the association (indirect effect: β = −0.047, p < .05); that is, the effect of ageism on psychological well-being was decreased from −.29 ( β , p < .001) to −.24 ( β , p < .001).

Lastly, Zhang et al. (2018) examined a moderating role of flexible goal adjustment (FGA) between age stereotypes and the well-being of older adults. FGA implies that individuals pursue their own personal goals, disengaging from goals that are incompatible with their preferences and altering their goals in response to unique conditions. Zhang et al. (2018) found that the interaction term, including FGA, was significant in predicting well-being ( β = .19, p < .01). Negative age stereotypes decreased the positive effect of positive age stereotypes on well-being for older adults with low FGA conditions, but the effect remained the same for individuals with high FGA.

Methodological Quality

Methodological quality was assessed using the JBI’s checklists. Table 6 presents a summary of the methodological qualities of the articles we reviewed. A total of eight methodological qualities were examined to assess the possibility of bias in the design, conduct, and analysis of reviewed studies. An inter-rater review process was implemented between two co-authors to assess the methodological quality of the reviewed studies. The total score of the Methodological qualities ranged from 0 to 8. Our reviewed articles ( N = 13) scored between 3 and 8, with mean scores of 6.1 ( SD = 1.3) and a median score of 7. Kim et al.’s (2015) study received all eight points, whereas Siguaw et al.’s (2017) study received three points. All studies met two of the criteria (b and h). All articles provided a clear explanation of how the study participants were selected or recruited. Additionally, the methods section was sufficiently detailed to enable us to identify the analytical techniques utilized. However, only 38% ( n = 5/13) successfully measured ageism in a valid and reliable manner.

Review of Methodological Quality.

a Were the criteria for inclusion in the sample clearly defined?

b Were the study subjects and the setting described in detail?

c Was the exposure measured in a valid and reliable way?

d Were objective, standard criteria used for measurement of the condition?

e Were confounding factors identified?

f Were strategies to deal with confounding factors stated?

g Were the outcomes measured in a valid and reliable way?

h Was appropriate statistical analysis used?

*Y: Yes; N: No; U: Unclear; N/A: Not applicable.

The first goal of this study was to locate studies that examined the relationship between ageism and older adults’ psychological well-being. A total of 13 studies were identified through a comprehensive search, and all of them empirically showed the negative effects of ageism on the psychological well-being of older adults. That is, older adults who perceived or experienced ageism were more likely to show lower levels of psychological well-being than those who did not perceive or experience ageism. Moreover, the psychological well-being of older people was adversely affected if they held internalized ageist thoughts.

The second goal of the study was to identify mediating or moderating factors between ageism and the psychological well-being of older adults. Five of the reviewed studies tested mediating or moderating effects of interventions between ageism and psychological well-being. Except for the coping responses, all mediating variables buffered the negative effects of ageism on psychological well-being in older adults. Age group identification ( Garstka et al., 2004 ), emotional reactions ( Kim et al., 2015 ), self-perception of aging and purpose in life ( Kim, 2015 ), body esteem ( Sabik, 2015 ), and flexible goal adjustment ( Zhang et al., 2018 ) were all identified as effective mediators to mitigate the negative effects of ageism on the psychological well-being.

To briefly synthesize the interventions, the psychological well-being of older adults (1) who were proud to be a member of their age group, (2) who experienced less negative emotions (i.e., feeling hurt, angry, sad, frustrated, humiliated, discouraged, terrified, foolish, or ashamed), (3) who considered aging process positively and held a positive view of their future, (4) who had greater body esteem, and (5) who had high levels of flexible goal adjustment were less negatively influenced by ageism. These mediators can inform intervention developments that will lessen the effects of ageism and improve older adults’ psychological well-being.

Scholars who investigate the extent of the detrimental impacts of ageism on older adults have focused on developing effective interventions in recent years ( Bujang, Sa’at, & Bakar, 2017 ). For instance, Burnes et al.’s (2019) systematic review of interventions to reduce ageism against older adults found that aging education toward young people and intergenerational contact were effective approaches for adolescents and young adults. However, it remains a question whether education and intergenerational contact can fully reduce the effects of ageism on older adults. In addition, during the COVID-19 pandemic, maintaining contact between generations has been an increasingly challenging endeavor. Thus, it is important to discuss how the negative effects of ageism among older adults during the pandemic. We believe that the intervention results of our study can be used as a basis for implementing innovative strategies to reduce ageism’s pernicious effects among older adults during periods of social distancing. These effects may result in a necessity for effective interventions in older adults, such as education for positive aging, emotional management, boosting body confidence, and flexible goal setting that may serve as downstream factors to mitigate or perhaps reverse negative effects of ageism on their psychological well-being. Our review also provides theoretical frameworks that enable a deeper understanding of the role of ageism in psychological well-being. One of these is the stress process model ( Kim, 2015 ). Recurrent experiences of ageism can be a stressor, and exposure to these stressful events could lead to depressive symptoms ( Kim, 2015 ). Unlike other stressors, ageism cannot be resolved only at the individual level. All age groups should be involved in addressing issues regarding ageism because it is one of the most socially condoned and institutionalized forms of prejudice that is reflected in many areas of society ( Nelson, 2005 ). The stereotype embodiment framework also helps us understand how ageism inhibits the psychological well-being of older adults. Stereotype embodiment refers to a person’s internalization of age stereotypes through life-long exposure ( Levy, 2009 ). This tends to adversely affect older adults psychologically, behaviorally, and physiologically. That is, when older adults endorse negative stereotypes, they are more likely to experience a broader range of adverse health outcomes.

Through the review process, we found that the research on the relationship between ageism and the psychological well-being of older adults is at an early stage with ample room for development. The number of identified quantitative studies was small, and most studies identified were conceptual. Considering that ageism is an immediate societal issue, more quantitative studies that provide generalizable empirical evidence are needed. Additionally, very few interventions regarding mediating or moderating factors between ageism and psychological well-being have been identified. That is, no definitive answer has been given for an effective method to deal with the negative effects of ageism. The need to develop an effective intervention as a buffer against the negative effects of ageism has increased due to the pervasive ageism in current society. Finding a way to mitigate or end the negative effects of ageism, especially on the psychological well-being of older adults, would provide additional insight into successful aging.

We also found the measurement of ageism to be insufficient. Among our identified studies, Kim et al. (2015) , Lee and Kim (2016) , and Lyons et al. (2018) used Palmore (2001) ’s ageism measure, and Zhang et al. (2018) and Zhang et al. (2019) used the Levy’s et al. (2004) Image of Aging Scale. Palmore’s (2001) measure and Levy’s et al. (2004) measure assess ageism from different perspectives. While Palmer examined discrimination experienced by older adults, the Images of Aging Scale by Levy et al. (2004) could be completed by respondents of any age and asked to rate the degree to which the words or phrases are representative of older adults. That is, Zhang et al. (2018) and Zhang et al. (2019) adopted and revised ageism scales that were specifically designed to measure the attitudes of younger people toward older people. Similarly, Bai et al. (2016) employed a measure of “perceptions of aging as a burden” to examine internalized ageism of older adults. Palmore’s (2001) scale was the only one to examine how older adults felt and responded to being perceived as a stereotype. However, Palmor’s (2001) scale is inadequate since it does not account for all aspects of ageism, and because of the ambiguous terminology, it is difficult to determine how the original meaning of the items was meant to be understood ( Kang, 2020 ). Except for the five studies, other studies in this review used not established scales such as uni-dimensional or simple measures. Ageism is a subjective concept, which requires considerable effort to measure accurately. Considering that ageism can be assessed using cognitive, behavioral, and informative components, a comprehensive set of constructs is necessary, as these constructs contain reliable and valid indicators.

Several limitations were identified in this systematic review. In our search, we identified a limited number of studies; whereas a comprehensive search was conducted, we found only thirteen studies that met the criteria for inclusion. Although we aimed to include all potentially relevant studies through a comprehensive search using a wide range of search strategies, some literature could not be included. For example, we were not able to include studies in languages other than English. Further, we found several articles that discussed the ageism of older adults aged 50+ or 55+. Our review also found many qualitative studies on ageism. Therefore, we suggest that future researchers might consider setting an age cutoff of 50 for the review, which would provide a larger number of studies to consider. In addition, research will be conducted to review more diverse forms of evidence, both quantitatively and qualitatively. Using qualitative research methods can also help to deepen the understanding of ageism, which is an extremely subjective concept.

From our review, we found that ageism can be a significant threat to the well-being of older adults. Ageism is negatively associated with older adults’ psychological health, causing mental health issues such as depression and anxiety and well-being in a negative way. Considering the growing mental health needs of older adults, future research needs to focus on establishing an effective preventive intervention against ageism. The importance of reducing or preventing ageism is often noted ( Nelson, 2005 ; Raposo & Carstensen, 2015 ), but few specific methods or variables have been presented that might help to reduce ageism, especially from the perspective of older adults. The results from the systematic review contribute to building a literature base that can be used to guide future research on developing interventions for older adults.

In light of the rapid growth of aging people, research on ageism should receive greater attention. While ageism, unlike sexism or racism, is a problem that all individuals may potentially face ( Nemmers, 2005 ), its importance has been neglected, and there is much less research on ageism than on sexism and racism ( Kim, 2009 ). Significant scholarly attention should be given to ageism, considering its importance and universality, as it encompasses every generation and the growth of the population of older adults. At this important moment, this systematic review lays the foundation for future work on ageism against older adults.

Appendix B. 

PRISMA 2020 Item Checklist

Note. The PRISMA 2020 item checklist is from Page et al. (2021) .

Declaration of Conflicting Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding: The author(s) received no financial support for the research, authorship, and/or publication of this article.

Hyun Kang https://orcid.org/0000-0003-3804-7165

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