BACKGROUND:

Physical activity may help maintain cognitive function and decrease dementia risk, but epidemiological findings remain controversial. The aim of our study was to investigate the association between leisure-time physical activity at midlife and the subsequent development of dementia and Alzheimer's disease (AD).

METHODS:

Participants were randomly selected from the survivors of a population-based cohort previously surveyed in 1972, 1977, 1982, or 1987. 1449 persons (72.5%) age 65-79 years participated in the re-examination in 1998 (mean follow-up, 21 years). 117 persons had dementia and 76 had AD. Multiple logistic regression methods were used to analyse the association between leisure-time physical activity and dementia or AD.

FINDINGS:

Leisure-time physical activity at midlife at least twice a week was associated with a reduced risk of dementia and AD (odds ratio [OR] 0.48 [95% CI 0.25-0.91] and 0.38 [0.17-0.85], respectively), even after adjustments for age, sex, education, follow-up time, locomotor disorders, APOE genotype, vascular disorders, smoking, and alcohol drinking. The associations were more pronounced among the APOE epsilon4 carriers.

INTERPRETATION:

Leisure-time physical activity at midlife is associated with a decreased risk of dementia and AD later in life. Regular physical activity may reduce the risk or delay the onset of dementia and AD, especially among genetically susceptible individuals.