We examined the association of purpose in life with risk of incident AD in more than 900 community-dwelling older persons. During up to 7 years of follow-up, greater purpose in life was associated with a substantially reduced risk of AD such that a person with a high score (90th percentile) on the purpose in life measure was approximately 2.4 times more likely to remain free of AD than was a person with a low score (10th percentile). The association of purpose in life with AD persisted after adjustment for several important covariates (ie, depressive symptoms, neuroticism, social network size, and number of chronic medical conditions) and in sensitivity analyses in which we excluded persons who developed AD during the first 3 years of follow-up. Furthermore, in subsequent analyses, purpose in life was associated with a reduced risk of incident MCI, an early preclinical manifestation of AD. Finally, in models that controlled for baseline level of cognitive function, we found that purpose in life was associated with a less rapid rate of cognitive decline in persons without AD and in persons without AD or MCI. These findings suggest that the tendency to derive meaning from life's experiences and to possess a sense of intentionality and goal directedness are associated with a substantially reduced risk of AD and a less rapid rate of cognitive decline in old age.
Emerging data suggest that psychological and experiential factors are related to the risk of AD, with some (eg, neuroticism, loneliness, social isolation, and depressive symptoms) increasing risk and others (eg, conscientiousness, extraversion, and social integration) decreasing risk. Purpose in life is an indicator of human thriving that has long been hypothesized to buffer against adverse health outcomes.5-14
In recent years, purpose in life has been conceptualized as a component of psychological well-being9-11
; in this context, purpose in life has been shown in cross-sectional studies to be associated with psychological health, including happiness, satisfaction, personal growth, self-acceptance, and better sleep.9-12,14
Although prospective data on the association of purpose in life with health outcomes are limited, we recently reported14
that purpose in life was associated with a reduced risk of all-cause mortality in older persons from this cohort. We are not aware of any previous study that has examined the association of purpose in life with risk of AD.
The finding that purpose in life is associated with cognitive outcomes may have important public health implications. In particular, these findings may provide a new treatment target for interventions aimed at enhancing health and well-being in older adults. Purpose in life is a potentially modifiable factor that may be increased via specific behavioral strategies that help older persons identify personally meaningful activities and engage in goal-directed behaviors. Even small behavioral modifications ultimately may translate into an increased sense of intentionality, usefulness, and relevance. Furthermore, purpose in life may be modifiable, even in persons for whom participation in more effortful activities (ie, physical activity, volunteerism, and other activities involving travel outside the home or local area) may be limited because of underlying health problems. Thus, purpose in life may offer a new treatment focus and may represent a target accessible to most of the aging population. If true, the implications could be far reaching, and efforts to increase purpose in life may help reduce the rapidly increasing burden of cognitive impairment in old age.
At present, the biological basis of the association of purpose in life with AD is unknown. Purpose in life is hypothesized to provide protective benefit in the face of illness or disease because it contributes to the optimal functioning of multiple physiologic systems.11,20,24
Although relatively few data are available on the association of purpose in life with physiologic measures, emerging evidence suggests that psychological well-being in general and purpose in life in particular are associated with important disease-related biomarkers.5,6,9
For example, purpose in life is negatively associated with immune markers, including salivary cortisol and the proinflammatory cytokines interleukin-6 receptor in women older than 75 years.26-28
In addition, purpose in life is positively correlated with high-density lipoprotein cholesterol levels and negatively with waist-hip ratios. Immune function and vascular health are related to cognitive function and the risk of dementia in old age,29
and it is possible that purpose in life is associated with a reduced risk of AD via its beneficial effect on these systems. However, future studies are needed to elucidate the biological basis of the association of purpose in life with cognition. In addition, because purpose in life is a potentially modifiable factor that all persons experience to some degree,30
future studies could examine potential strategies (eg, facilitation of participation in personally meaningful activities and goal setting) to increase purpose in life in older persons.
This study has some notable strengths, including the assessment of purpose in life in a large group of community-dwelling older persons free of dementia at baseline who underwent detailed annual structured clinical evaluations to document incident AD. Cognitive function was assessed at evenly spaced intervals using psychometrically sound composite measures for up to 8 years with high rates of follow-up participation, which enhanced our ability to reliably characterize individual paths of cognitive decline. Finally, we assessed purpose in life using a standard scale previously shown to have predictive validity for adverse health outcomes in older persons.14
One limitation of the study is the selected nature of the cohort, which may have restricted the range of scores on the purpose in life measure and may limit the generalizability of findings. In addition, there are factors that we did not measure (eg, apathy, motivation, and spirituality or religiosity) that may affect the associations of purpose in life with health outcomes. Recent data have shown that apathy, a syndrome of decreased motivation and interest, is common in persons with early cognitive impairment (ie, MCI and early AD) and is associated with functional status.31,32
Apathy and other lifestyle factors (eg, exercise and nutrition) may be related to the level of engagement in purposeful behaviors and may have implications for our understanding of the link between purpose in life and cognition. Finally, an inherent limitation of this study, as in all epidemiologic studies, is the inability to establish causality with certainty. Note that purpose in life was protective against AD even when examined carefully in a series of sensitivity analyses and after controlling for several important covariates; however, our ability to make causal inferences is limited. Future studies are needed to further clarify the role of apathy and other lifestyle factors as they relate to purpose in life and to examine the biological basis of the association of purpose in life with adverse health outcomes in old age.