Understanding temporal changes in intrinsic capacity: analysis of domain-specific intrinsic capacity using SHARE data

Global population aging challenges acute, disease-centric healthcare models and highlights the need for functional markers of aging. The World Health Organization's intrinsic capacity (IC) framework, encompassing cognition, vitality, locomotion, psychological well-being, and sensory function, provides a multidimensional measure of functional reserve. However, most longitudinal studies have collapsed IC into a single score, limiting insight into domain-specific trajectories and interrelationships. In this longitudinal cohort study, we examined 7-year changes in composite and domain-specific IC scores, stratified by age and sex, and assessed associations between changes across domains among community-dwelling adults aged 50 years and older participating in the Survey of Health, Ageing and Retirement in Europe (SHARE). The analytic sample included 27,107 participants (56.5% women; mean age 65.1 ± 8.2 years) with complete IC data at baseline (Wave 6, 2015) and follow-up (Wave 9, 2022). IC was operationalized as a 0-50 composite score derived from five domains, each standardized to a 0-10 scale using SHARE-specific measures. Over 7 years, composite IC declined statistically significantly (mean difference - 1.57 points; 95% CI - 1.63 to - 1.50; p < 0.001), with greater decline in men than women (- 1.71 vs - 1.46; p < 0.001). Locomotion domain contributed most to overall decline across age groups. Changes in vitality were moderately correlated with changes in locomotion (r≈0.30) and psychological well-being (r≈0.25), suggesting that vitality may function as a physiological node linking physical and psychological domains. These findings demonstrate that IC declines progressively from midlife, with steeper trajectories in men, and support domain-specific monitoring to better characterize age-related functional decline.