Abstract

Background: Alzheimer disease and other dementing disorders are major sources of morbidity and mortality in aging societies. Proven strategies to delay onset or reduce risk for dementing disorders would be greatly beneficial. Objective: To determine whether regular exercise is associated with a reduced risk for dementia and Alzheimer disease. Design: Prospective cohort study. Setting: Group Health Cooperative, Seattle, Washington. Participants: 1740 persons older than age 65 years without cognitive impairment who scored above the 25th percentile on the Cognitive Ability Screening Instrument (CASI) in the Adult Changes in Thought study and who were followed biennially to identify incident dementia. Measurements: Baseline measurements, including exercise frequency, cognitive function, physical function, depression, health conditions, lifestyle characteristics, and other potential risk factors for dementia (for example, apolipoprotein E ε4); biennial assessment for dementia. Results: During a mean follow-up of 6.2 years (SD, 2.0), 158 participants developed dementia (107 developed Alzheimer disease). The incidence rate of dementia was 13.0 per 1000 person-years for participants who exercised 3 or more times per week compared with 19.7 per 1000 person-years for those who exercised fewer than 3 times per week. The age- and sex-adjusted hazard ratio of dementia was 0.62 (95% CI, 0.44 to 0.86; P = 0.004). The interaction between exercise and performance-based physical function was statistically significant (P = 0.013). The risk reduction associated with exercise was greater in those with lower performance levels. Similar results were observed in analyses restricted to participants with incident Alzheimer disease. Limitations: Exercise was measured by self-reported frequency. The study population had a relatively high proportion of regular exercisers at baseline. Conclusion: These results suggest that regular exercise is associated with a delay in onset of dementia and Alzheimer disease, further supporting its value for elderly persons.