Discovering how certain health factors contribute to functional declines may help to promote successful aging. To determine the independent and joint associations of handgrip strength (HGS) and cognitive function with instrumental activities of daily living (IADL) and activities of daily living (ADL) disability decline in aging Americans. Data from 18,391 adults aged 50 years and over who participated in at least one wave of the 2006–2014 waves of the Health and Retirement Study were analyzed. A hand-held dynamometer assessed HGS and cognitive functioning was examined with a modified version of the Telephone Interview of Cognitive Status. IADL and ADL abilities were self-reported. Participants were stratified into four distinct groups based on their HGS and cognitive function status. Separate covariate-adjusted multilevel models were conducted for the analyses. Participants who were weak, had a cognitive impairment, and had both weakness and a cognitive impairment had 1.70 (95% confidence interval (CI) 1.57–1.84), 1.97 (CI 1.74–2.23), and 3.13 (CI 2.73–3.59) greater odds for IADL disability decline, respectively, and 2.26 (CI 2.03–2.51), 1.26 (CI 1.05–1.51), and 4.48 (CI 3.72–5.39) greater odds for ADL disability decline, respectively. HGS and cognitive functioning were independently and jointly associated with IADL and ADL disability declines. Individuals with both weakness and cognitive impairment demonstrated substantially higher odds for functional decline than those with either risk factor alone. Including measures of both HGS and cognitive functioning in routine geriatric assessments may help to identify those at greatest risk for declining functional capacity.
