Cognitive Function as a Predictor of Major Mobility Disability in Older Adults: Results From the LIFE Study

Background and Objectives: Many cross-sectional studies have confirmed a link between gait speed and cognitive function. However, it is unknown whether cognitive function plays a role in the onset of major mobility disability (MMD) and if the effects are independent of physical function. This study examined cognitive and physical function as predictors of MMD across an average of 2.6 years of follow-up in community-dwelling older adults with compromised mobility. Research Design and Method: Data were collected from 1,635 participants in the Lifestyle Interventions and Independence for Elders (LIFE) study ages 70-89 years free of MMD at baseline. MMD was assessed every 6 months and defined as the inability to walk 400 m in <= 15 min without assistance or sitting. Cognitive function was assessed at baseline, 18 months, and 24 months using a cognitive battery categorized into four domains: global cognitive function, processing speed, verbal memory, and executive function. Results: Across the study duration of 2.6 years, 536 participants (32.8%) developed MMD. Cox Proportional Hazard models indicated a protective relationship for higher baseline processing speed (Hazard Ratio [HR] per standard deviation: 0.86, p = .006), executive function (HR: 0.86, p = .002), and global cognition (HR: 0.85, p = .001) on incidence of MMD adjusted for demographics, intervention, and comorbidities. Results were not significant after adjustment for gait speed. In adjusted longitudinal models, a positive change in processing speed was significantly associated with reduced risk of MMD (HR: 0.52, p < .001) while other domains were not. Discussion and Implications: In the LIFE study, processing speed at baseline and follow-up was a significant predictor of subsequent MMD although the observed association may be explained by physical function as reflected in gait speed. More studies are needed to understand how cognitive function, alone and in combination with physical function, influences risk of MMD.