The Association Between Race/Ethnicity and Risk of Type 2 Diabetes in Women Varies by BMI: A Pooled Analysis of Individual Data From 15 Cohort Studies

OBJECTIVE: To examine the association between race/ethnicity and type 2 diabetes risk in women and assess the interaction between race/ethnicity and BMI. RESEARCH DESIGN AND METHODS: We analyzed individual-level data from 730,408 women across 15 cohort studies. Six racial/ethnic groups were identified: White, Chinese, Japanese, South/Southeast Asian, Black, and mixed/other. Cox proportional hazards models with study as a random effect were used to estimate hazard ratios (HRs) for type 2 diabetes associated with race/ethnicity. The joint association of race/ethnicity and BMI was assessed using BMI categories incorporating Asian-specific cutoffs (<18.5, 18.5-22.9, 23.0-24.9, 25.0-27.4, 27.5-29.9, and ≥30 kg/m2), with White women having a BMI of 18.5-22.9 kg/m2 as the reference. RESULTS: Overall, 37,329 women (5.1%) were diagnosed with type 2 diabetes. By age 70, the cumulative incidence was highest among South/Southeast Asian (24.6%) and Black women (23.6%), with baseline obesity rates of 40.0% (BMI ≥27.5 kg/m2) and 45.6% (BMI ≥30 kg/m2), respectively. After adjusting for BMI, South/Southeast Asian women had the highest diabetes risk compared with White women (HR 4.13, 95% CI 3.78-4.51), while other racial/ethnic groups had about twice the risk. Joint effect analysis showed South/Southeast Asian women with a BMI ≥23 kg/m2 had a substantially greater diabetes risk than other racial/ethnic groups with the same BMI, especially those with BMI 27.5-29.9 kg/m2 (HR 23.17, 19.21-27.95) and ≥30 kg/m2(HR 35.52, 30.57-41.28). CONCLUSIONS: South/Southeast Asian women have a markedly elevated risk of type 2 diabetes, further amplified by modestly higher BMI, highlighting the need for ethnicity-specific diabetes prevention strategies for women.