Association Between Frailty Index and New-Onset Stroke in Middle-Aged and Elderly Chinese Adults with Gastrointestinal or Liver Diseases: A Longitudinal Cohort Study

Background: Although the frailty index (FI) has been reported to associate with stroke risk in older adults, its relationship in those with gastrointestinal (GI) or liver diseases remains unclear. We examined this association in a Chinese cohort with these comorbidities. Methods: Using baseline data from the China Health and Retirement Longitudinal Study (CHARLS) 2011, we included participants aged ≥45 years with GI or liver diseases. Cox proportional hazards models, restricted cubic splines, and likelihood ratio tests were applied to evaluate the association between FI and new-onset stroke risk. Results: A total of 3682 participants were included (mean age 58.78 ± 9.3 years; 55.78% female). Over a mean follow-up of 8 years, 9.26% experienced a stroke. FI was significantly associated with new-onset stroke risk in a non-linear manner (likelihood ratio test p < 0.001), with an exploratory threshold identified at FI = 0.18 (95% CI: 0.1–0.2). Below this threshold, each 0.1-unit increment in FI was strongly associated with elevated stroke risk (HR = 2.10, 95% CI: 1.56–2.82, p < 0.0001); above it, the association plateaued and was no longer significant (HR = 1.10, 95% CI: 0.99–1.22, p = 0.079). These results remained robust across subgroup and sensitivity analyses. Conclusions: This study demonstrates a significant non-linear association between FI and new-onset stroke risk in middle-aged and elderly individuals with GI or liver diseases, highlighting the importance of FI assessment in this population.