Association between Body Roundness Index and Functional Impairment in Older Adults: Exploring the Potential Mediating Role of Systemic Inflammation Response Index

BACKGROUND: Functional impairment (FI) represents a major health challenge among older adults. OBJECTIVES: This study aimed to investigate the association between the body roundness index (BRI), a novel indicator of central obesity, and FI, as well as to examine the mediating role of the systemic inflammation response index (SIRI) in this relationship. METHODS: Data were obtained from the NHANES (1999-2018), comprising 15,110 older adults. BRI was calculated using waist circumference and height. FI was defined based on physical limitations, basic activities of daily living, and instrumental activities of daily living. SIRI was derived from peripheral blood cell counts. Weighted multivariable logistic regression, restricted cubic spline (RCS) curves, subgroup analyses, mediation analysis, and sensitivity analyses were performed. RESULTS: Among the participants, 9734 individuals were identified as having FI. In the fully adjusted model, BRI was significantly positively associated with the presence of FI [odds ratio (OR): 1.70; 95% confidence interval (CI): 1.60, 1.80]. A similar positive association was observed between SIRI and FI (OR: 1.23; 95% CI: 1.16, 1.32). RCS curves revealed a nonlinear dose-response relationship between BRI and FI (P-overall < 0.001; P-nonlinearity < 0.001) and between SIRI and FI (P-overall < 0.001; P-nonlinearity = 0.016). Notably, mediation analysis indicated that SIRI partially mediated the association between BRI and FI in older adults (indirect effect = 0.00116; P < 0.001; mediated proportion = 2.23%). CONCLUSIONS: These findings may help elucidate the potential mechanisms linking central obesity to FI in older adults, offering insights for targeted prevention of functional disability.