Association between weight-adjusted waist index (WWI) and multimorbidity: Evidence from NHANES and prospective validation in CHARLS

WWI remained a significant and consistent predictor of multimorbidity, demonstrating greater discriminatory ability than BMI or WC. While RCS suggested a predominantly linear association, GAM revealed potential non-linearity at extreme WWI levels, indicating that dose-response patterns warrant further confirmation. Validation in the CHARLS cohort supports temporal association, offering greater causal plausibility. Collectively, these results highlight WWI as a practical marker for identifying high-risk individuals and for guiding early prevention strategies.