Frailty index is positively associated with stroke risk in nationally representative cohorts from the united States and China.

Frailty has been linked to adverse health outcomes, but its relationship with stroke remains insufficiently understood in general populations. In this study, we examined the association between frailty and stroke using two nationally representative cohorts: the U.S. National Health and Nutrition Examination Survey (NHANES) and the China Health and Retirement Longitudinal Study (CHARLS). Frailty was assessed using a multidimensional frailty index, analyzed both continuously and by category. Weighted logistic regression and restricted cubic spline models were applied. We found that higher frailty index scores were associated with greater odds of stroke in both populations, independent of demographic and clinical risk factors. The association appeared remained consistent in multiple sensitivity and subgroup analyses. Each 0.1-unit increase in the frailty index was associated with a 2.90-fold and 1.78-fold higher odds of stroke in NHANES and CHARLS, respectively. While CHARLS provides prospective evidence supporting the temporal relationship between frailty and stroke, the cross-sectional nature of NHANES limits causal inference. Overall, these findings suggest that frailty may be a useful marker for identifying individuals at higher risk of stroke. Further research is needed to validate its predictive utility and to explore whether modifying frailty can help reduce stroke incidence, particularly in aging populations.