Background: The purpose of this study is to examine whether physical disability is associated with faster rate of decline in cognitive function.
Methods: A longitudinal population-based cohort of 6,678 initially nondisabled older adults from a biracial urban community was interviewed at 3-year intervals from 1993 to 2012. Cognitive function was assessed using a standardized global cognitive score, and physical disabilities using activities of daily living (ADL) and instrumental activities of daily living (IADL).
Results: During the follow-up period, 2,450 of 6,678 participants (37%) developed ADL and 2,069 of 4,287 participants (48%) developed IADL disability. After adjusting for demographic and physiologic confounders, cognitive function declined a mean of 0.048 unit per year before ADL disability and 0.047 unit per year before IADL disability. In comparison, the rate of cognitive decline accelerated further by 0.076 unit per year (156% increase) after ADL disability and 0.054 unit per year (115% increase) after IADL disability. Severity of ADL and IADL disabilities were also associated with faster cognitive decline following disability.
Conclusions: In old age, cognitive function declines substantially faster following physical disability even after controlling for demographic and physiologic characteristics of participants.