Larson EB, Wang L, Bowen J, McCormick WC, Teri L, Crane P, Kukull W
Circulation. 2006;144(2):73-81.
Background:
Alzheimer disease and other dementing illnesses are major sources of morbidity and mortality among the aging population. Effective prevention strategies would result in substantial benefits through improved quality of life, prolonged independent life expectancy, and reduced economic cost and social burdens. Evidence from some longitudinal studies and randomized trials suggest that regular physical exercise enhances cognitive function in older adults.
Objective:
The purpose of this study was 2-fold: (1) to determine whether regular exercise is associated with a reduced risk for incident dementia and (2) to examine whether the association of physical exercise with the incidence of dementia is modulated by other potential risk factors.
Methods:
The Adult Changes in Thought study is a population-based, longitudinal study of aging and dementia. A random sample of individuals ages 65 years and older was drawn from Seattle-area members of a consumer-governed health maintenance organization. Individuals with an existing diagnosis of dementia or were current residents of a nursing home were excluded. Participants were screened for cognitive function; persons scoring above the 25th percentile on the Cognitive Ability Screening Instrument were enrolled. Physical function was assessed at baseline by questionnaire. Biennial examinations were performed to identify cases of incident dementia.
Results:
A total of 1,740 persons were followed for a mean of 6.2 years. One hundred fifty-eight (9%) participants developed dementia; 107 developed Alzheimer disease. The incidence rate of dementia was 13.0 per 1,000 person-years for persons who exercised >=3times per week, compared with 19.7 per 1,000 person-years for persons who exercised <3 times per week. The age- and sex-adjusted hazard ratio of dementia for the regular exercise group was 0.62 (confidence interval 0.44-0.86, P = .004). When potential confounders (including presence of apolipoprotein E [varepsilon]4 alleles, diabetes, hypertension, cerebrovascular disease, coronary heart disease, self-rated health, physical performance, and depression) were adjusted for, the hazard ratio of dementia for the regular exercise group was 0.68 (confidence interval 0.48-0.96, P = .03). The interaction of exercise and Physical Performance Functioning score was statistically significant (P = .013). The risk of reduction of dementia with exercise was greater among participants with lower Physical Performance Functioning scores than among those with higher Physical Performance Functioning scores.
Discussion:
This study found a 32% reduction in the risk of dementia for persons who exercised 3 or more times per week. An interesting finding is the effect modification seen between exercise and physical functioning in relation to incident dementia. There was greater risk reduction of dementia by exercise among participants who had lower levels of physical functioning at baseline. This suggests that one of the ways that regular exercise might reduce the risk of dementia is through modulating the relationship between physical functioning and dementia. These results suggest that regular exercise is associated with a delay in the onset of dementia. Physicians and health-promotion programs might find these data valuable as they seek truly effective ways to promote physical activity among their patients.
Comment:
This is an observational cohort study that contributes to the evidence that regular physical exercise is associated with a lower risk of dementia. However, one limitation relates to the measure of exercise intensity, which was obtained only through self-reported frequency. Generalizability is also limited because data were obtained from a predominantly white, well-educated cohort with a relatively high proportion of regular exercisers at baseline. Nevertheless, this study is supported by recent findings that report that the area of the brain most susceptible to ischemic damage (the hippocampus) is also the earliest areas of the brain affected by Alzheimer disease; this area had less tissue loss in older persons at higher levels of physical conditioning. The authors point out that Alzheimer disease is one of the most feared illnesses of aging and is frequently cited as a reason for not wanting to "get old." Hence, public dissemination of a possible preventive strategy for this condition, by increasing physical activity, with all of its health benefits, may capture a wider audience.
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