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