Weight-Adjusted Waist Index Outperforms Conventional Adiposity Indices in Predicting All-Cause Mortality: A Population-Based Cohort Study.

BACKGROUND: Body mass index (BMI), the most widely used adiposity metric, cannot differentiate fat distribution from lean mass, limiting its prognostic utility. This study compared the weight-adjusted waist index (WWI) with BMI, waist-to-height ratio, and relative fat mass (RFM) as predictors of all-cause and cardiovascular mortality using a z-standard-ized framework. METHODS: Data from 18 496 adults aged ≥20 years from the National Health and Nutrition Examination Survey 2011-2018 were linked to the National Death Index through December 31, 2019. Four adiposity indices were z-standardized and analyzed using survey-weighted Cox models with sequential adjustment. Dose-response relationships were assessed using restricted cubic splines, and subgroup analyses examined the effect modification by sex, multimorbidity, and estimated glomerular filtration rate (eGFR). RESULTS: Over a median follow-up of 4.83 years, 976 all-cause and 291 cardiovascular deaths occurred. Weight-adjusted waist index demonstrated the strongest association with all-cause mortality (hazard ratio [HR] 1.34; 95% CI 1.23-1.46; P < .001); BMI and RFM did not reach significance. After mutual adjustment, WWI retained its association (HR 1.40; P < .001) while BMI did not reach statistical significance in the adjusted model. Weight-adjusted waist index showed a linear dose-response relationship, contrasting the J-shaped curve of BMI. The association was consistent across subgroups but attenuated in participants with eGFR < 60 (interaction P = .034). CONCLUSION: Weight-adjusted waist index was the strongest independent predictor of all-cause and cardiovascular mortality among 4 adiposity indices. Its linear dose-response relationship, consistency across subgroups, and calculability from waist circumference and body weight alone support its use as a practical alternative to BMI for mortality risk stratification.