Trends in trajectories and incidence of functional impairment in middle-aged Americans

The prevalence of functional impairment (i.e., difficulty performing daily activities such as bathing and dressing) has increased among middle-aged Americans, but longitudinal data are lacking. The objective of this study was to examine trajectories of functional status and incidence of functional impairment among middle-aged adults across 4 birth cohorts. We conducted a cohort study of 14,707 participants ages 50-56 enrolled between 1992-2010 in the nationally representative Health and Retirement Study (HRS) who were independent at baseline in self- or proxy-reported basic activities of daily living (ADLs, score 0-6) and instrumental ADLs (IADLs, score 0-5). Participants were born in one of four birth cohorts: "Pre-War Babies," 1935-1941; "War Babies," 1942-1947; "Early Baby Boomers," 1948-1953; or "Mid Baby Boomers," 1954-1959. Primary outcomes were trajectories of functional status (number of ADL and IADL difficulties) and incidence of functional impairment (difficulty with ≥1 ADLs or ≥1 IADLs) before age 65. We used group-based trajectory models to identify distinct classes of ADL change and multinomial logistic regression models to examine association of birth cohort with group membership. From the earliest to latest birth cohort, the percentages excluded at baseline due to prevalent functional impairment were 13.8%, 9.9%, 9.6%, and 11.7%. Mean age among participants was 53.2 years, 51.6% were women, 9.9% identified as Black, and 8.0% as Latino. In adjusted and unadjusted analyses, Pre-War Babies and War Babies were at significantly higher risk of belonging to trajectory groups with higher levels of impairment versus Mid Boomers. Over a median follow-up of 7.6 years, average annual incidence rates for ADL impairment from earliest to latest cohort were 2.0%, 0.7%, 0.7%, and 1.0%. Findings were similar for IADLs. Functional trajectories and incidence of functional impairment improved from earlier to later birth cohorts. Findings suggest differing risk factors for mid-life prevalent versus incident functional impairment.