Muscle Strength and Later Incident Dementia and Related Mortality: The Cooper Center Longitudinal Study.

Background: This study aimed to examine the longitudinal association between muscle strength, incident dementia, and dementia-related mortality among community-dwelling adults.

Methods: This prospective cohort study included 7755 participants (20-90 y) participating in the Cooper Center Longitudinal Study (1980-1990) and enrolled in Medicare between 1999 and 2019. Upper and lower body strength was measured with 1-repetition isotonic maximum bench and leg press. Relative muscle strength was computed relative to body weight and categorized into tertiles based on previously established age and sex normative data. Earliest indication of dementia and dementia-related mortality were determined with Medicare Administrative Claims Data and the National Death Index. The associations of muscle strength with incident dementia and dementia-related mortality were determined using an illness-death model with random frailty.

Results: Participants were predominantly White (97%) and male (86%), with an average age of 44 years at baseline. The mean duration between baseline muscle strength assessment and Medicare surveillance was 23 years. The incidence of all-cause dementia was 18.2 per 1000 person-years. Individuals in the medium tertile of lower body strength had reduced hazard of all-cause dementia (hazard ratio = 0.84; 95% CI, 0.72-0.98) relative to the low tertile, controlling for cardiovascular risk factors. Yet, the association was marginally significant (hazard ratio = 0.86; 95% CI, 0.73-1.0) when further controlled for cardiorespiratory fitness. There were no associations between body strength and dementia-related mortality.

Conclusions: No associations of upper and lower body muscle strength with the risk of dementia and related mortality were observed after adjusting for cardiovascular risk factors and cardiorespiratory fitness.