Although the scientific literature is replete with references to healthy aging, actually measuring the phenomenon is challenging. Unless one wishes to limit the study of healthy aging to those with near-perfect health, one must find a balance between “what is possible” and the reality that as people grow older decrements in health are likely to occur. Although, for instance, some older adults remain free of chronic illness until very late in life, over 80% of older adults have at least one chronic condition (18
). Thus, although it is “possible” to remain disease free into older adulthood, it is unlikely for most—especially as one reaches advanced old age. More importantly, the mere presence of any particular decrement in health may be relatively inconsequential for both the individual and larger society.
In this investigation, we examined four definitions of healthy aging—all informed by Rowe and Kahn's concept of successful aging (4
). Specifically, we assessed how relaxing the operational criteria affects prevalence estimates, demographic patterns in healthy aging, and the validity of the concept. Not surprisingly, we found that the measured prevalence of healthy aging increased steadily as we relaxed the criteria, rising from 3.3% to 35.5%. To the extent that definitions of healthy aging are used to identify segments of the population that might benefit from intervention efforts, these differences are not trivial. Using the definition that we refer to as Rowe and Kahn’s, roughly 1 million older Americans were classified as experiencing healthy aging in 2006. For Level III Healthy Aging, that number increased to over 11 million.
Across definitions, the odds of healthy aging were lower among those of advanced age, those with lower levels of education, and women than for their corresponding counterparts. These findings are consistent with a broad literature documenting higher levels of disease and functional limitations among those of advanced age and those with lower levels of education (see, eg, 18
) and a higher prevalence of functional health problems among older women (21
), suggesting that our definitions are capturing known health disadvantages in the older population.
We found a complex pattern of results by race and ethnicity. Although Hispanic adults had significantly lower odds of meeting the criteria for our purely functional definition of healthy aging, no significant difference was evident for definitions that incorporated disease prevalence. This finding is consistent with work documenting as good or better chronic disease profiles but worse functional health among Hispanic older adults, with differences in the latter often attenuated when factors such as socioeconomic status are controlled (see, eg, 19
). In contrast with Hispanic–white differences, black older adults generally had significantly lower odds of meeting each definition than older white adults. The magnitude of the difference varied by definition, however, with the difference most striking for the definition that incorporated obesity and hypertension. Given the higher prevalence of hypertension among older black adults (22
) and obesity in older black women (23
), this is not unexpected. Variation in observed racial and ethnic differences highlight, however, how findings about racial and ethnic disparities in healthy aging may be particularly sensitive to the operational definition of healthy aging employed.
Although differing definitions and varying degrees of statistical adjustment make it difficult to compare findings across other recent studies (6
), healthy aging is generally reported to be lower among those of advanced age and lower socioeconomic status, which is similar to what we observed here. Gender differences tend to be less consistent, indicating that—like race and ethnicity—gender differences in healthy aging are sensitive to the measurement and analytic strategies employed. Even in this study—where we found that women had significantly lower odds of being classified as experiencing healthy aging across the conceptual continuum—the magnitude of the difference varied across definitions. The largest difference was for our purely functional definition (ie, Level III Healthy Aging), suggesting that gender differences in functional aspects of health are greater than differences in chronic disease prevalence as measured in this study.
We found that by using each definition, we were able to identify a group of older adults who were markedly less likely to report fair or poor health and to die over an 8-year period than their respective counterparts, providing evidence of the validity of all four definitions. For both self-rated health and death, the odds ratios were lowest for Rowe and Kahn's definition. This suggests that Rowe and Kahn's criteria—as operationalized herein—identified a subset of older adults with particularly low odds of adverse outcomes. It should be acknowledged, however, that the precision of the estimates for Rowe and Kahn's definition is lower than for the less stringent definitions due to the small number of older adults who meet the criteria.
Our analysis of the sensitivity and specificity of each definition in predicting mortality adds an additional dimension to our understanding of the validity of the definitions examined. Results indicate that the more stringent definitions were most sensitive (ie, those who died were readily classified as unhealthy in 1998) but least specific (ie, most of those who survived were not classified as healthy in 1998). In conjunction with the results of our examination of the odds of fair or poor self-rated health and death, these findings shed insight into how best to operationalize healthy aging. In particular, they support the use of definitions that emphasize freedom from symptomatic disease and functional limitations over those that incorporate more rigid disease criteria. The former identify a group of individuals for whom the odds of adverse outcomes are sizably diminished while, at the same time, reducing the chances of misclassifying healthy individuals as unhealthy—characteristics that are essential if one seeks to distinguish the truly healthy from the truly unhealthy. Although they would benefit from additional refinement, we believe that our Level II and Level III definitions provide a useful starting place for establishing a realistic benchmark for healthy aging.