Intrinsic Capacity Across 15 Countries in the Survey of Health, Aging, and Retirement in Europe.

Importance: Intrinsic capacity (IC) is a core component of the World Health Organization's healthy aging framework. Yet, despite multiple validations of IC across various settings, there is still a lack of longitudinal cross-national analysis. Objective: To validate the IC construct, describe variance between key demographic groups, and create population centile curves across 15 countries using data from the Survey of Health, Aging, and Retirement in Europe (SHARE). Design, Setting, and Participants: In this population-based multicenter cohort study, data from SHARE wave 5 (January to November 30, 2013) were analyzed, and subsequent care dependence in wave 6 (January to November 30, 2015) was determined. Adults 50 years and older from SHARE wave 5 with at least 1 available measure and follow-up data in SHARE wave 6 were included. Data analyses were conducted between December 11, 2022, and June 7, 2024. Exposure: SHARE waves 5 and 6. Main Outcomes and Measures: Changes in activities of daily living (ADL) and instrumental activities of daily living (IADL). Methods included structural equation modeling, bifactor analysis, and path analysis. Construct validity was tested through multiple linear regression and validity of estimates through mediation analysis. Centile curves were established using the generalized additive models for location, scale, and shape. Results: The sample included 64 872 eligible participants aged 50 to 104 years, with a mean (SD) age of 67.24 (10.01) years, of whom 35 976 (55.46%) were women. The bifactor confirmatory factor analysis model achieved good fit (comparative fit index, 0.986; Tucker-Lewis index, 0.981), suggesting an IC structure consisting of 1 general factor and 5 subdomains. Mediation analysis indicated that IC was associated with subsequent declining performance in ADL (standard coefficient [SD], -0.213 [0.002]; P < .001) and IADL (standard coefficient [SD], -0.209 [0.002]; P < .001) after adjusting for age, gender, educational attainment, socioeconomic status, and country. Socioeconomic status was associated with IC both within and between countries. Centile curves for IC by gender and country (5th, 10th, 25th, 50th, 75th, 90th, and 95th percentiles) were constructed. Conclusions and Relevance: Results of this cohort study of older adults suggest that IC was a valid and reliable measure that effectively captured individual-level aspects of functional ability. The centile curves developed during the study suggest that IC has the potential to serve as a benchmark for health status in older populations.