Independent and joint associations of social participation and depressive symptoms with incident stroke risk in older adults: a prospective cohort study based on CHARLS and ELSA

BACKGROUND: Stroke remains a leading cause of death and disability among older adults. Depressive symptoms and low social participation have been linked to stroke risk via behavioral and biological pathways. This study examined the independent and joint associations of social participation (SP) and depressive symptoms (DS) with incident stroke in two nationally representative cohorts. METHODS: Data were derived from two nationally representative cohorts: the China Health and Retirement Longitudinal Study (CHARLS; 2011-2018) and the English Longitudinal Study of Ageing (ELSA; 2012-2019). SP and DS were assessed at baseline and categorized into four phenotypic subgroups (SP+/DS-, SP-/DS-, SP+/DS+, SP-/DS+). Cox proportional hazards models were fitted within each cohort with sequential covariate adjustment. To address missing data, sensitivity analyses were performed using the multiple imputation method (MICE). RESULTS: In CHARLS (n = 10,555; mean age 58.3 years), DS + was associated with elevated stroke risk (Model 3 h = 1.40, 95% CI 1.18-1.65, p < 0.001), whereas SP- showed no significant association (HR = 1.14, 95% CI 0.96-1.34, p = 0.13). Compared with the SP+/DS- reference phenotype, the SP-/DS+ joint phenotype was associated with an increased stroke risk (HR = 1.56, 95% CI 1.27-1.93, p < 0.001). In ELSA (n = 5,321; mean age 65.1 years), SP - was not associated with stroke risk (HR = 1.05, 95% CI 0.74-1.51, p = 0.78), and DS+ exhibited a similar but non-significant association (HR = 1.54, 95% CI 0.95-2.51, p = 0.08); the SP-/DS + was associated with elevated stroke risk (HR = 1.87, 95% CI 1.04-3.37, p = 0.04). CONCLUSIONS: Depressive symptoms were associated with incident stroke, whereas low social participation alone showed no consistent association with incident stroke. Notably, the joint phenotype SP-/DS+ identified a subgroup with the highest incident stroke risk, although such associations exhibited some heterogeneity between cohorts.