Background: Loss of muscle strength is common and is associated with various adverse health outcomes in old age, but few studies have examined the association of muscle strength with the risk of Alzheimer disease (AD) or mild cognitive impairment (MCI).
Objective: To test the hypothesis that muscle strength is associated with incident AD and MCI.
Design: Prospective observational cohort study.
Setting: Retirement communities across the Chicago, Illinois, metropolitan area.
Participants: More than 900 community-based older persons without dementia at the baseline evaluation and in whom strength was measured in 9 muscle groups in arms and legs, and in the axial muscles and summarized into a composite measure of muscle strength.
Main outcome measures: Incident AD and MCI and the rate of change in global cognitive function.
Results: During a mean follow-up of 3.6 years, 138 persons developed AD. In a proportional hazards model adjusted for age, sex, and education status, each 1-U increase in muscle strength at baseline was associated with about a 43% decrease in the risk of AD (hazard ratio, 0.57; 95% confidence interval, 0.41-0.79). The association of muscle strength with AD persisted after adjustment for several covariates, including body mass index, physical activity, pulmonary function, vascular risk factors, vascular diseases, and apolipoprotein E4 status. In a mixed-effects model adjusted for age, sex, education status, and baseline level of global cognition, increased muscle strength was associated with a slower rate of decline in global cognitive function (P < .001). Muscle strength was associated with a decreased risk of MCI, the precursor to AD (hazard ratio, 0.67; 95% confidence interval, 0.54-0.84).
Conclusion: These findings suggest a link between muscle strength, AD, and cognitive decline in older persons.