Social connection and intrinsic capacity in later life across the USA, England, Europe, China, and Japan: a harmonised multicohort longitudinal study

Background Social connection represents a key modifiable determinant of healthy ageing, yet cross-national longitudinal evidence linking it to intrinsic capacity and its trajectories remains scarce. We examined whether baseline social connection was associated with baseline intrinsic capacity and annual intrinsic capacity change, whether associations differed across intrinsic capacity domains, and which components of social connection were most consistently associated with intrinsic capacity across cohorts. Methods The present study was a harmonised longitudinal cohort study using data from five ageing cohorts: the Health and Retirement Study (HRS; USA), English Longitudinal Study of Ageing (ELSA; England), Survey of Health, Ageing and Retirement in Europe (SHARE; Europe and Israel), China Health and Retirement Longitudinal Study (CHARLS; China), and Japanese Study of Aging and Retirement (JSTAR; Japan). Participants were aged 50 years or older. Baseline social connection was operationalised as a 0–5 composite score (marital or partnered status, living with others, family contact, friends or relatives contact, and social activity participation). Intrinsic capacity, encompassing locomotion, cognition, psychological, sensory, and vitality domains, was summed (0–10) and converted to cohort-specific and wave-specific Z scores. Survey-weighted linear mixed models with random intercepts estimated baseline associations adjusted for age, sex, educational attainment, household wealth tertile, and chronic disease burden. Trajectory models included time (years since baseline) and a social connection × time interaction. Cohort-specific estimates were pooled using random-effects meta-analysis with false discovery rate (FDR) control for domain tests. Findings Among 39 021 participants (CHARLS 5538; ELSA 3294; HRS 3015; SHARE 26 239; and JSTAR 935), baseline age ranged from 61·1 in CHARLS to 70·8 years in HRS, the weighted proportion of males from 44·2% in HRS to 56·9% in JSTAR across cohorts, and follow-up ranged from two years in JSTAR to 12 years in ELSA. Higher baseline social connection was associated with higher total intrinsic capacity at baseline (pooled β=0·04 SD per 1-point increase; 95% CI 0·03–0·06). Domain-specific associations were the strongest for psychological (β=0·05 SD; 95% CI 0·03–0·06) and cognition (β=0·03 SD; 95% CI 0·01–0·05) domains, both remaining statistically significant after FDR correction. Locomotion showed a smaller association (β=0·02 SD; 95% CI 0·00–0·04) that remained significant after FDR correction. By contrast, sensory and vitality showed weaker associations that did not remain significant after FDR correction. Baseline social connection was not associated with differential rates of intrinsic capacity change over follow-up (pooled slope difference β=0·0024 SD per year; 95% CI −0·0004 to 0·0053; I 2 =26·3%). Among the five social connection components, social participation (β=0·13 SD; 95% CI 0·10–0·15) and married or partnered status (β=0·06 SD; 95% CI 0·02–0·09) showed the most consistent associations with higher total intrinsic capacity and remained statistically significant after FDR correction. Interpretation Across diverse cultural contexts, stronger social connection is consistently associated with higher baseline intrinsic capacity, particularly in cognitive and psychological domains. By contrast, we found no clear evidence that baseline social connection predicted differential rates of intrinsic capacity decline over follow-up. These findings support greater attention to social connection in healthy ageing policies and community services while recognising the need for further evidence on whether strengthening social connection can improve intrinsic capacity. Funding Department of Medicine & Therapeutics Geriatric Research Fund; CUHK Vice-Chancellor's Discretionary Fund.