Multi-trajectories of intrinsic capacity and their impact on incident disability in community-dwelling older adults in Japan

BACKGROUND: The World Health Organization's intrinsic capacity (IC) framework has shifted focus from functional deficits to preserving abilities in ageing. However, the trajectories of IC and their impact on disability remain insufficiently explored. Therefore, we aimed to examine variability in IC trajectories and their impact on incident disability among community-dwelling Japanese older adults. METHODS: We analyzed 1056 disability-free community-dwelling older adults (aged 65-89 years) from the National Institute for Longevity Sciences-Longitudinal Study of Aging who completed three or more surveys between waves 2-7 (2000-2012), using their final assessment as baseline for disability follow-up. Using group-based multi-trajectory modelling, we obtained IC trajectories across six domains: cognition, locomotion, vitality, vision, hearing, and psychological well-being. Incident disability was confirmed through the Long-term Care Insurance System certificate over a 17.5-year maximum follow-up period. Multivariable-adjusted cause-specific Cox proportional hazards models and Fine-Gray subdistribution hazard models (to account for the competing risk of mortality) were employed to investigate the relationships between IC trajectories and incident disability. RESULTS: We identified four distinct IC trajectories: preserved (60.5 %), hearing-decline (15.9 %), physio-psychological decline (17.5 %), and global decline (6.1 %). During a median 9.8-year follow-up, 380 (36.0 %) participants developed disabilities. Compared to "preserved group" (reference), the "hearing-decline" and "physio-psychological decline" groups had notably higher disability risks, with multivariable-adjusted hazard ratios (aHR) and 95 % confidence intervals (CI) of 1.53 (1.17-1.99) and 1.66 (1.26-2.18), respectively. While the risk for the "global decline group" was not statistically significant in the cause-specific Cox model (aHR 1.41; 95 % CI 0.96-2.08), it became significant after accounting for the competing risk of mortality (Subdistribution aHR 1.56; 95 % CI 1.09-2.22). Time-stratified analyses revealed differential patterns: during the first two years of follow-up, "physio-psychological decline group" and "global decline group" exhibited significantly higher risks of incident disability, whereas beyond two years, elevated risks were observed in "hearing decline group" and "physio-psychological decline group". CONCLUSIONS: This study identified four distinct IC trajectories among older adults. After accounting for mortality as a competing risk, all declining patterns showed higher disability risks than non-declining ones, and their time-varying relationships with disability onset highlight the importance of IC-pattern-based assessments and targeted interventions tailored to specific decline patterns to prevent disability in ageing populations.