Relationship between body roundness index and mortality rates and life expectancy in populations with metabolic syndrome.

Background: Cardiovascular Disease (CVD) represents a significant global public health challenge. Metabolic Syndrome (MetS) notably elevates the risk of CVD, with MetS patients facing approximately 2-3 times the risk compared to the general population. Body Roundness Index (BRI), a novel anthropometric marker, has recently gained attention; However, its comprehensive association with mortality risk in MetS populations remains incompletely elucidated. Methods: This longitudinal study analyzed data from 10 consecutive cycles of the National Health and Nutrition Examination Survey (NHANES) between 1999 and 2018, comprising 19,535 participants with MetS. We employed Cox proportional hazards regression models to elucidate the association between BRI and mortality risk. Nonlinear relationships were comprehensively examined using smooth curve fitting and two-segment Cox regression models to identify potential threshold effects. Life table analysis was utilized to calculate life expectancy by levels of the BRI, with multiple sensitivity analyses performed to validate the robustness and consistency of the primary findings. Results: BRI demonstrated a U-shaped association with mortality risk (P for nonlinearity <0.001), with the highest quintiles showing markedly increased all-cause (HR: 1.29, 95% CI: 1.12-1.48) and cardiovascular mortality risk (HR: 1.39, 95% CI: 1.13-1.73). BRI and BMI performed similarly in predicting all-cause mortality (AUC: 0.810 vs. 0.802, P = 0.18). Gender-stratified analyses revealed significant effect modification (P < 0.001): males in Q5 exhibited a 56% increased mortality risk (HR: 1.56, 95% CI: 1.30-1.87) and a 3.8-year reduction in life expectancy at age 45, while females in Q4 showed a protective effect (HR: 0.77, 95% CI: 0.66-0.90) and females in Q5 demonstrated only a modest 0.9-year life expectancy reduction. Conclusion: Our findings demonstrate a U-shaped association between BRI and all-cause and cardiovascular mortality in individuals with MetS. Notably, BRI showed comparable predictive performance to BMI for all-cause mortality in this population. Maintaining an optimal BRI level may be associated with improved survival outcomes.