Abstract
OBJECTIVES: Impairments in specific tasks that are necessary for independent living may identify future self-care limitations, and the use of time-varying covariates can better capture the fluidity in functional capacity trajectories over time. The purpose of this study was to determine the associations between individual instrumental activities of daily living (IADL) impairments and time to activities of daily living (ADL) disability for middle-aged and older adults in the United States. DESIGN: Longitudinal panel. SETTING: Detailed interviews that included physical, biological, and psychosocial measures were completed in person. The core interview was typically completed over the telephone. PARTICIPANTS: A nationally representative sample of 15,336 adults aged at least 50 years from the 2006 wave of the Health and Retirement Study was followed for 8 years. MEASURES: Ability to perform IADL and ADL were self-reported at each wave. Separate covariate-adjusted Cox models were used to examine the time-varying associations between individual IADL impairments and time to ADL disability. RESULTS: The presence of each IADL impairment was associated with a higher hazard ratio for an ADL disability for the following functions: 2.52 [95% confidence interval (CI) 2.35, 2.70] for grocery shopping, 1.91 (CI 1.77, 2.06) for preparing hot meals, 1.55 (CI 1.37, 1.76) for taking medications, 1.48 (CI 1.36, 1.61) for managing money, 1.41 (CI 1.27, 1.57) for using a telephone, and 1.38 (CI 1.29, 1.48) for using a map. CONCLUSIONS/IMPLICATIONS: Our findings provide insights into the disabling process by revealing how impairments in each IADL are differentially associated with time to ADL disability. Interventions aiming to retain function during aging should be informed by fluctuations in IADL performance and how specific IADL impairments may exacerbate functional capacity declines more so than others.