Frailty Index Changes Before and After Stroke: Findings from Four Cohorts covering 18 Countries

Background: Frailty is a dynamic predictor of adverse stroke outcomes, but its bidirectional relationship with stroke—how frailty progresses before and after stroke—remains underexplored. Aims: This study aims to examine longitudinal frailty index (FI) trajectories in individuals with and without stroke, and changes in frailty trajectories within individuals before and after a stroke event across four international longitudinal studies. Methods: This prospective cohort study analyzed data from four longitudinal cohorts: CHARLS, ELSA, HRS, and SHARE. Frailty progression was assessed using validated FI scores. Incident strokes were identified through self-reported doctor diagnoses. Linear mixed models were used to evaluate changes in FI before and after stroke. Results: Among the 73,961 participants, 4374 (5.9%) incident stroke events were identified. Compared to stroke-free individuals, stroke survivors exhibited an observable increase in FI prior to the stroke event (e.g., CHARLS: β = 0.016/year, 95% CI: 0.014–0.017). A sharp increase in FI occurred during the incident stroke event (HRS: β = 0.078, 95% CI: 0.074–0.083), followed by sustained post-stroke acceleration (ELSA: β = 0.019/year, 95% CI: 0.016–0.022). Sensitivity analyses confirmed robustness across cohorts. Conclusions: Frailty accelerates significantly both before and after an incident stroke, suggesting a bidirectional relationship between stroke and frailty. Integrating frailty assessment into stroke risk stratification, rehabilitation, and secondary prevention to optimize patient outcomes, particularly in ageing populations. Data access statement: The datasets generated and analyzed during the current study are available on the HRS website ( https://hrs.isr.umich.edu/ ), CHARLS ( https://charls.pku.edu.cn/en ), SHARE ( https://share-eric.eu/ ), and ELSA ( https://www.elsa-project ).