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

Objectives Functional impairment (FI) represents a major health challenge among older adults. This study aims 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 National Health and Nutrition Examination Survey (NHANES, 1999–2018), comprising 15,110 older adults. BRI was calculated using waist circumference and height. FI was defined based on physical limitations (PL), basic activities of daily living (BADL), and instrumental activities of daily living (IADL). 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, 9,734 individuals were identified as having FI. In the fully adjusted model, BRI was significantly positively associated with the presence of FI (OR = 1.70, 95% 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 for nonlinearity < 0.001) and between SIRI and FI (P overall < 0.001; P for 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 functional impairment in older adults, offering insights for targeted prevention of functional disability.