Association of Erythrocyte Distribution Width with the Albumin-to- Ratio (RAR) and Osteoporosis: Mediation by Obesity Indicators (BRI/ABSI)

Abstract Background: The Albumin-to-Ratio (RAR) value represents an innovative composite indicator defined as the ratio of red blood cell distribution width (RDW) to serum albumin（SA）. Recent research has highlighted its potential as a biomarker in cardiovascular and metabolic diseases. However, the influence of RAR on the incidence of osteoporosis(OP) remains uncertain. Furthermore, the Body Roundness Index (BRI) and the Abdominal Body Shape Index (ABSI) are modern indicators of obesity that consider fat distribution. Our study aims to explore the relationship between RAR and OP, while also examining the mediating role of BRI and ABSI in this association. Methods: In this study, data were sourced from the National Health and Nutrition Examination Survey (NHANES), spanning the period from 2007 to 2018. The analysis was based on a cross-sectional design and included a cohort of 14,549 adult participants. We applied multivariate logistic regression, subgroup analyses, smoothed curve fitting, and mediation analyses to examine both linear and nonlinear relationships between RAR and the prevalence of OP, while also assessing the mediating effects of obesity indicators (BRI and ABSI) in this association. Results: We found a negative correlation between RAR and the incidence of osteoporosis, with an odds ratio (OR) of 1.44 (95% CI: 1.14-1.83, P = 0.003), indicating that higher RAR values are associated with increased OP risk. Restricted cubic spline (RCS) analysis confirmed that this relationship is linear. Subgroup analyses consistently demonstrated a similar trend across various demographics. Moreover, mediation analysis revealed a partial mediating effect of the Body Roundness Index (BRI) and the Abdominal Body Shape Index (ABSI) on the relationship between RAR and OP incidence, with mediation ratios of 15.89% for BRI and 9.83% for ABSI. Conclusion:The study established that elevated levels of RAR are significantly linked to the prevalence of osteoporosis in the adult population in the United States, indicating its potential as a cost-effective screening biomarker. Mediation analysis demonstrated that ABSI and BRI accounted for 9.8% and 15.9% of this association, respectively, suggesting that central obesity may contribute to bone loss through RAR-related