Nonlinear associations between obesity indices and fall risk in middle-aged and older Chinese adults: a cross-sectional analysis based on CHARLS

Background: Falls are a leading cause of disability and mortality among older adults in China. The mechanisms linking various obesity indices—such as BMI, Waist-to-Height Ratio (WHtR), Body Roundness Index (BRI), and Body Fat Percentage (BFP) — to fall risk remain unclear. Given the limitations of BMI, it is important to investigate the influence of body composition and central obesity indicators on fall risk. Methods: This cross-sectional study used data from the China Health and Retirement Longitudinal Study (CHARLS, 2011–2016; n = 27,303). Logistic regression, restricted cubic spline (RCS) modeling, and piecewise regression were applied to explore the nonlinear associations between obesity indices and falls. Covariates including demographic and health-related factors were adjusted for in multivariate models. Results: WHtR, BRI, and BFP were nonlinearly associated with fall risk, while BMI showed no significant relationship. Inflection points were observed at 0.504 for WHtR, 3.06 for BRI, and 28.6% for BFP. Below these thresholds, increases in WHtR and BFP were associated with reduced fall risk; above the thresholds, fall risk increased significantly. Subgroup analyses indicated stronger associations among women, rural residents, and individuals with arthritis. Conclusion: Our findings identify WHtR, BRI, and BFP as more sensitive predictors of fall risk than BMI. Thresholds of BRI ≥ 3.0 and BFP ≥ 28% may serve as clinical screening markers for fall prevention, supporting a shift from BMI-centric to integrated body composition-function assessments.