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.

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.

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.

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. Competing Interest Statement The authors have declared that no competing interests exist. Funding Statement The author(s) received no specific funding for this work. Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethical approval for the original CHARLS project was granted by the Peking University Biomedical Ethics Committee (IRB00001052-11015), and all participants provided written informed consent. Our current work is a secondary analysis of the fully anonymized, publicly available CHARLS data. We combined data from CHARLS waves conducted in 2011-2012, 2013-2014, and 2015-2016. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data Availability All data files are available from the CHARLS database(https://charls.pku.edu.cn/)