Association between intrinsic capacity and disability before death among older adults: a decedent cohort study

Background Intrinsic capacity is inversely associated with disability; however, little is known about how the magnitude of this association varies before death. We aimed to use time-varying effect modelling (TVEM), a statistical tool for capturing dynamic patterns of change, to evaluate the association between intrinsic capacity and disability as a function of time before death. Methods In this decedent cohort study, we included participant data from the Precipitating Events Project in the USA. Community-dwelling individuals aged 70 years and older who were initially free of disability in four activities of daily living (bathing, dressing, transferring from a chair, and walking around the house) were included in the study. Individuals with substantial cognitive impairment and without an available proxy, with a life expectancy of less than 12 months, who had plans to relocate, or who were unable to speak English were excluded. Participants who had died by Dec 31, 2024, were included in the analytical sample. Intrinsic capacity was assessed at baseline and subsequently at 18-month intervals for up to 306 months (except at 126 months) using 25 items. Intrinsic capacity scores (0–100) were derived using Bayesian multilevel item response theory. Disability, defined as dependence in instrumental activities of daily living, was assessed monthly. TVEM was applied to evaluate the association between intrinsic capacity and disability, anchored to participants' time of death. Results are presented as time-varying adjusted odds ratios reflecting the increase (or decrease) in the log-odds of disability corresponding to a 10-point increase in intrinsic capacity, controlling for covariates. Findings Of the 1002 eligible individuals, 754 were enrolled between March 23, 1998, and Oct 26, 1999; data from 746 participants who died by Dec 31, 2024, were included in the analyses. Among the 746 decedents, 479 (64%) were women, 267 (36%) were men, and 675 (90%) were White. Trajectories using a backwards timescale spanning 20 years showed a gradual decline in mean intrinsic capacity from 80 (95% CI 77–83) points to 47 (45–48) points and a non-linear rise in the probability of disability. Higher intrinsic capacity was associated with significantly lower odds of disability from around 13·6 years before death onwards. The inverse association between intrinsic capacity (per 10-point increase) and disability strengthened as death approached. In the final 4 years of life, adjusted odds ratios corresponding to a 10-point increase in intrinsic capacity ranged from 0·56 (95% CI 0·46–0·68) to 0·58 (0·50–0·68). Interpretation The association between intrinsic capacity and disability emerged approximately 14 years before death, suggesting that intrinsic capacity could serve as an early marker of functional decline and guide the development of targeted interventions. Funding National Institute on Aging.