This cohort study used data from the nationally representative Health and Retirement Study (HRS) to examine how functional status changed and how frequently new functional impairment occurred among middle-aged U.S. adults born between 1935 and 1959. The primary outcomes were trajectories of difficulty in basic activities of daily living (ADLs) and instrumental ADLs (IADLs), and the incidence of new functional impairment (defined as difficulty with ≥1 ADL or ≥1 IADL) before age 65.
Participants (n = 14,707) were ages 50–56 at enrollment and were recruited into the HRS between 1992 and 2010. All included participants were independent at baseline by self- or proxy-report for basic ADLs (score range 0–6) and IADLs (score range 0–5). Birth cohorts were defined as: Pre-War Babies (1935–1941), War Babies (1942–1947), Early Baby Boomers (1948–1953), and Mid Baby Boomers (1954–1959).
Across the analytic sample the mean age was 53.2 years. Slightly more than half were women (51.6%). Racial and ethnic composition included 9.9% identifying as Black and 8.0% identifying as Latino. Further demographic or clinical breakdowns beyond these figures were not reported in the abstract.
The investigators applied group-based trajectory models to identify distinct classes of change in the number of ADL and IADL difficulties over time. To assess the association between birth cohort and trajectory-group membership, multinomial logistic regression models were used. The primary analytic focus was on incident functional impairment occurring before participants reached age 65.
Individuals with prevalent functional impairment at baseline were excluded from the incident analyses. The proportions excluded at baseline because of existing functional impairment differed by birth cohort and, from earliest to latest cohort, were: 13.8%, 9.9%, 9.6%, and 11.7%.
Group-based trajectory analysis identified distinct patterns of ADL and IADL change over the follow-up period. In both unadjusted and adjusted analyses, participants from the earliest cohorts (Pre-War Babies and War Babies) were more likely to belong to trajectory groups characterized by higher and worsening levels of impairment compared with the reference group of Mid Baby Boomers. Specific trajectory shapes, numbers of groups, and the absolute counts of participants within each trajectory class were not detailed in the abstract.
Over a median follow-up of 7.6 years, the average annual incidence rates for new ADL impairment by cohort from earliest to latest were reported as 2.0%, 0.7%, 0.7%, and 1.0%. The authors report that findings for IADL impairment were similar to those for ADLs, although exact incidence percentages for IADLs were not provided in the abstract.
The analysis showed that being born in earlier cohorts (Pre-War and War Babies) conferred significantly higher risk of membership in higher-impairment trajectory groups relative to Mid Baby Boomers. These associations persisted after adjustment for covariates in the models. Exact adjusted odds ratios, confidence intervals, and the covariates included in adjustment were not listed in the abstract.
The study reports an overall improvement in functional trajectories and lower incidence of new functional impairment in later birth cohorts compared with earlier cohorts. This pattern suggests that risk of developing new ADL and IADL difficulties in mid-life may be declining across these birth cohorts. The authors note that these cohort patterns imply differing determinants for prevalent mid-life functional impairment versus incident impairment occurring before age 65, but specific causal factors were not described in the abstract.
The abstract does not provide details on several important items: the specific covariates used in adjusted models, absolute numbers in each trajectory group, precise IADL incidence estimates, methodology specifics for trajectory modeling (number of groups selected, model fit criteria), and potential mechanisms or risk factors underlying cohort differences. Information on sensitivity analyses, handling of missing data, or subgroup analyses (for example by sex or race/ethnicity) is also not reported in the abstract.
Among 14,707 HRS participants ages 50–56 who were independent at baseline, trajectories of functional status and incidence of new ADL and IADL impairment generally improved from earlier birth cohorts to later birth cohorts. Pre-War Babies and War Babies were at higher risk of following trajectories with greater impairment compared with Mid Baby Boomers. The study highlights cohort-level improvements in mid-life functional outcomes and suggests that drivers of prevalent versus incident functional impairment may differ; further detail on underlying factors was not provided in the abstract.