Body Mass Index-Specific Central Adiposity and Risk of Incident Type 2 Diabetes Among Aging Women

CONTEXT: Body mass index (BMI) does not capture central adiposity, which may provide additional information for type 2 diabetes (T2D) risk stratification. OBJECTIVE: To evaluate BMI-specific waist circumference (WC) categories in relation to incident T2D and assess their performance across independent cohorts. METHODS: Prospective analyses included 133,620 Women's Health Initiative (WHI) participants free of T2D at baseline, randomly assigned to training (70%; n=93,463) and test (30%; n=40,157) samples. External validation included the Health and Retirement Study (HRS; n=2,885) and Healthy Aging in Neighborhoods of Diversity across the Life Span (HANDLS; n=1,037). Cox models estimated T2D risk across BMI and BMI-specific WC categories. Discrimination was assessed using Harrell's C-statistic. RESULTS: In WHI, T2D risk increased progressively across BMI categories (adjusted hazard ratios [HRs], 1.51-3.30) and joint BMI-WC categories (HRs, 1.40-4.43). Within BMI strata, higher WC generally identified greater T2D risk. Associations were directionally consistent in HRS and HANDLS. Age modified associations, with stronger gradients at younger ages, whereas race and ethnicity interactions were not statistically significant. Model discrimination was modest (C-statistics approximately 0.60-0.75). CONCLUSIONS: BMI-specific WC categories refine adiposity-related T2D risk stratification beyond BMI alone but provide modest individual-level discrimination. WC may complement BMI in identifying women warranting more comprehensive metabolic risk assessment rather than serving as a stand-alone T2D prediction tool.