“Successful Aging”—Where Next?

The idea of “successful aging” has been the subject of research for a broad range of academic disciplines for more than 3 decades. Early mention of “successful aging” can be found in the work of social scientists in the United States during the 1960s and 1970s.1-6 During the 1980s and 1990s, psychologists and behavioral scientists addressed successful aging.7-11 Over the last 2 decades, physicians and health services researchers have contributed to theories of successful aging.12-19 In recent years, this concept has gained increased attention, likely because of a combination of demographic trends and social forces. Baby boomers—those born between 1946 and 1965—face the prospect of surviving to very old age, and those who have already reached the age of 65 have a life expectancy of an additional 16 to 20 years.20 Furthermore, analyses using longitudinal data suggest that, in addition to living longer, people are healthier and more active than before and that rates of disability and institutionalization will continue to fall in the future.21-24 Finally, older adults are more highly educated than previous generations and are interested in health-related matters.25 Because of this combination of circumstances, healthcare providers may find their patients seeking information about how to age successfully. Some patients may want to apply scientific findings to their own situations to maximize their personal likelihood of aging successfully. We therefore conducted a review of published literature that has attempted to define successful aging and the factors that might predict success. Articles were identified from the following sources: (1) MEDLINE search (using the key terms “successful aging,”“normal aging,”“theories of aging,”“centenarians”); (2) psycINFO search (using the same key terms as in (1)); (3) on-line card catalog search (using the key term “aging”) of the University of Washington libraries, which contain over 1.9 million book titles; (4) recommendations from local reviewers of the manuscript; and (5) reference lists of all articles and books found by the procedures just described. No exclusions were made for year of publication. Studies were excluded if they used a definition of successful aging that had already been identified, if they focused on a related concept (e.g., healthy aging, effective aging, elite aging) but made no mention of the term “successful aging,” or if they were not published in English. We were not seeking to provide a comprehensive literature review on lifestyle factors that promote healthy aging. Neither did we intend to propose a definition of successful aging or argue for the validity of the concept of successful aging—as a stand-alone construct or in comparison with other related, but nonetheless distinct, concepts such as healthy aging. Rather, our intent was simply to identify and present in a highly summarized format the many and varying definitions of successful aging that have been put forth in the literature over the past 30 to 40 years. We intend this summary to be a succinct reference for clinicians who care for aging adults and researchers engaged in the study of aging. In addition, we offer a rationale for exploring the public's definition(s) of successful aging; we also suggest questions and design considerations for those seeking to pursue further work related to this concept. Four decades of literature yield a variety of definitions of successful aging. Table 1 outlines the key elements of the various definitions. We made two observations in comparing the various ways in which successful aging has been operationalized in past research. First, although several definitions emphasize maintenance of functional capacity as an essential element of success, no single, uniform, operational definition of “success” has been adopted. Studies of predictors of successful aging, wherein high-level functioning constitutes part of the definition of success, identify physical activity, social engagement, and freedom from chronic illness as predictors with some regularity (Table 2), whereas these same elements constitute how other researchers define success. Second, we observed that very little work has been done to ascertain the views of aging individuals.26-29 The relevance to aging individuals of the various definitions of successful aging thus remains uncertain. Why would the absence of a common definition of successful aging among behavioral and clinical scientists be relevant to clinicians and researchers? Simply being aware that there is no consensus on a definition of successful aging has relevance for clinicians. It points to the importance of discussing directly with patients their values and ideals related to the aging process, including their personal conception of successful aging, to ensure that there is mutual understanding of their health goals and priorities for the latter years of life. Additionally, clinicians could consider periodically reassessing their patients' ideas of what it means to age successfully. We know that one feature of individuals who achieve personal satisfaction as they age is the ability to modify their goals in accordance with changing personal circumstances.30 This would be of interest particularly if studies with aging individuals determined that beliefs change with age. For their part, researchers should recognize that, thus far, investigative work has used a composite outcome variable based on a given investigator's own definition of success and that empirical validation of that definition has not been documented. Researchers need to be aware that predictors of successful aging will depend on the way the outcome—successful aging—is defined. Future research in the area of successful aging should attempt to compare the definitions of successful aging of aging individuals themselves with those developed by the research community. An intriguing issue will be how to validate definitions if there are substantial discrepancies, but, overall, the perceptions of those undergoing the aging process will be critical in determining the relevance of researchers' definitions and most importantly, the practical value of research using this term. Inquiries into older individuals' perspectives on the meaning of “successful aging” are important next steps. It is possible, for instance, that successful aging may be a fluid concept for individuals as they age and that individuals' definitions may vary substantially by birth cohort, gender, ethnic subgroup, and the presence or absence of various chronic diseases. Exploratory research could be conducted to examine the relevance and meaning of success among different subgroups of aging individuals at different phases of the life span (i.e., middle, young-old, old, and old-old age). Cohorts of aging individuals could be reinterviewed periodically to assess whether within-individual variation in the definition of success occurs with the passage of time. Cross-cultural comparisons may be informative, particularly if comparisons were made between cultures that honor their older people (such as Asian cultures) and the American culture, which in general seeks to defy or deny aging. An important question, in light of the centrality of maintenance of function in the definitions of many researchers, would be whether individuals who experience functional loss believe they can still age successfully. Additional questions that should be addressed include the following. What role do the setting of new goals during one's later years, the history of a career filled with achievements, full- or part-time work during “retirement,” self-perceived health, economic hardship, and mandatory retirement play in older peoples' definition of success? Do definitions of successful aging have any predictable relationship to mortality? Do definitions influence healthcare-seeking behavior? How do aging individuals react to the term “successful aging”? An important first question would be, Do aging individuals find the term successful aging relevant and meaningful, or completely unacceptable? If the latter, what alternative term might they propose? Although researchers have operationalized the term in a variety of different ways, “successful aging” remains a value judgment for many. Beliefs of aging individuals about the meaning and relevance of “successful aging” have not been systematically documented. The face validity of the term, and an empirical understanding of its utility and relevance, could be enhanced if beliefs of the lay public were elicited and compared with and incorporated into researchers' def- initions. Asking aging individuals about the meaning and relevance of successful aging should enrich the theoretical definitions that have predominated on this concept that has potentially high relevance to persons of all ages, allowing a more patient-centered definition of successful aging to emerge. A clearer understanding of patients' beliefs about what constitutes successful aging should enhance providers' ability to choose from an array of healthcare recommendations those that are most relevant to their individual patients. A patient-centered definition will also be essential for future research in the field of successful aging, for it will allow determination of predictors truly relevant to persons who are aging. An enriched definition should increase our appreciation of a perspective that has not been elicited in work thus far. Such an understanding is critical to effective provider-patient communication and the provision of health care to an increasingly informed older population.