Association between a novel obesity index WWI and chronic kidney disease in a Chinese middle-aged and older population: a national prospective cohort study

Obesity is a significant risk factor for chronic kidney disease (CKD), but traditional body mass index (BMI) cannot distinguish between muscle and fat mass. Weight-adjusted waist index (WWI), as a novel obesity indicator, better reflects central adiposity and body composition; however, its longitudinal association with CKD incidence remains unclear, particularly regarding sex differences. This study utilized prospective cohort data including middle-aged and older adults with a median follow-up of 8.0 years. WWI was categorized into sex-specific quartiles. Prior to covariate adjustment, the log-rank test and Kaplan-Meier curves were used to assess cumulative risk of CKD incidence across WWI groups. Cox proportional hazards models were employed to evaluate the association between WWI and CKD risk. CKD was defined as estimated glomerular filtration rate < 60 mL/min/1.73 m² or self-reported kidney disease during follow-up. Results showed that WWI was significantly associated with CKD incidence in females, with hazard ratios of 1.56 (95%CI 1.04–2.34), 1.59 (95%CI 1.08–2.34), and 1.53 (95%CI 1.01–2.31) for Q1, Q3, and Q4, respectively, compared with Q2, whereas no significant association was observed in males. ROC curve analysis demonstrated that WWI (AUC = 0.80) exhibited superior predictive performance for CKD in females compared with traditional obesity indices BMI (AUC = 0.78) and WC (AUC = 0.79) (P < 0.05). Sensitivity analyses confirmed the robustness of these findings. This study suggests that WWI is an independent predictor of CKD risk in middle-aged and older women, providing a novel anthropometric indicator for renal disease prevention and control in female populations.