Frailty Index and Risk of Ischemic Stroke in China: Evidence from a Cohort Study, Disease Burden Analysis, and Mendelian Randomization

Objective: This study aims to examine the association between the frailty index (FI) and stroke risk among Chinese adults, describe the burden of stroke in China, and explore the causal role of FI in ischemic stroke through Mendelian randomization. Methods: Data from the China Health and Retirement Longitudinal Study (CHARLS) included 13,473 participants aged 45 years and older without a history of stroke. Cox models, restricted cubic splines, and sensitivity analyses were employed to assess the association between the modified frailty index (mFI) and incident stroke. Additionally, data from the Global Burden of Disease (GBD) 2021 data report were utilized to describe stroke trends in China from 1990 to 2021. Two-sample Mendelian randomization was conducted to evaluate the causal effects of FI on ischemic stroke subtypes. Results: During a median follow-up period of approximately 7 years, 811 incident strokes were recorded. Each 0.1-point increase in mFI was associated with a 16% increase in stroke risk (HR = 1.16, 95% CI: 1.06–1.27), demonstrating a linear dose–response relationship. From 1990 to 2021, the proportion of ischemic stroke rose from 46.9% to 63.2%. Mendelian randomization analysis provided genetic evidence supporting a causal association between FI and ischemic stroke (OR = 1.191, 95% CI: 1.046–1.357), particularly driven by large-artery atherosclerotic (OR = 1.852) and small-vessel stroke (OR = 1.415), but not by cardioembolic stroke. Conclusions: A higher FI is associated with an increased risk of stroke among Chinese adults, with genetic evidence supporting a causal role in ischemic stroke. Therefore, FI may serve as a valuable addition to existing risk assessment tools.