Association of Body Roundness Index with all-cause and cardiovascular mortality in patients with cardiovascular-kidney-metabolic (CKM) syndrome stages 0–3: a cohort study

Objective: This study aimed to investigate the association of body roundness index (BRI) with all-cause and cardiovascular mortality in patients with cardiovascular-kidney-metabolic (CKM) syndrome stages 0–3. Methods: We analyzed data from 18,984 participants in the National Health and Nutrition Examination Survey (NHANES) from 2003 to 2018. We employed Cox proportional hazards models, Fine-Gray proportional subdistribution hazards models, restricted cubic splines (RCS), and subgroup analysis to examine the associations between BRI and all-cause and cardiovascular mortality in patients with CKM syndrome stages 0–3. Results: Over a median follow-up of 7.5 years, 1756 all-cause and 471 cardiovascular deaths were documented. Cox and Fine-Gray models revealed a significant positive association between the BRI and both all-cause and cardiovascular mortality after full adjustment. RCS indicated a U-shaped nonlinear relationship between BRI and all-cause mortality (P for nonlinear <0.0001), while a linear association was observed with cardiovascular mortality (P for nonlinear = 0.0635). Threshold analysis identified an inflection point at BRI = 5.68. BRI levels below 5.68 showed a negative correlation (HR = 0.90, 95% CI: 0.83–0.96, P = 0.0024); above 5.68 BRI was positively correlated (HR = 1.12, 95% CI: 1.08–1.17, P < 0.0001). Subgroup analyses revealed significant interactions (P for interaction <0.05) whereby the association was strongest among participants with less than high school diploma and current drinkers (for all-cause mortality), and among younger participants(< 50 years) and current smokers (for cardiovascular mortality). Conclusion: In CKM syndrome stages 0–3, BRI shows a U-shaped link to all-cause mortality but a linear association with cardiovascular mortality.