Nonlinear association between body roundness index and all-cause mortality in myocardial infarction survivors: A cohort study based on NHANES 1999-2018.

While anthropometric indices predict cardiovascular mortality, the novel body roundness index (BRI)'s association with all-cause mortality in myocardial infarction (MI) survivors remains unknown. This cohort study analyzed 2099 National Health and Nutrition Examination participants (1999-2018) with prior MI. Mortality was ascertained via National Death Index linkage (median follow-up ~ 9 years). Using Cox regression with covariate adjustment and penalized splines, we identified an L-shaped BRI-mortality relationship with an inflection point at 3.99. Below this threshold, each 1-unit BRI increase significantly reduced mortality risk (hazard ratio = 0.62, 95% CI: 0.50-0.75, P  < .0001). Above 3.99, BRI showed no association (hazard ratio = 1.02, 95% CI: 0.98-1.06, P = .4242). This threshold pattern persisted in subgroups. Our findings first demonstrate that lower BRI was associated with higher mortality in MI survivors, suggesting maintaining BRI above critical thresholds may confer survival benefits.