Sex hormone-binding globulin and risk of clinical diabetes in American black, Hispanic, and Asian/Pacific Islander postmenopausal women.

BACKGROUND Recent prospective studies have shown a strong inverse association between sex hormone-binding globulin (SHBG) concentrations and risk of clinical diabetes in white individuals. However, it remains unclear whether this relationship extends to other racial/ethnic populations. METHODS We evaluated the association between baseline concentrations of SHBG and clinical diabetes risk in the Women's Health Initiative Observational Study. Over a median follow-up of 5.9 years, we identified 642 postmenopausal women who developed clinical diabetes (380 blacks, 157 Hispanics, 105 Asians) and 1286 matched controls (777 blacks, 307 Hispanics, 202 Asians). RESULTS Higher concentrations of SHBG at baseline were associated with a significantly lower risk of clinical diabetes [relative risk (RR), 0.15; 95% CI, 0.09-0.26 for highest vs lowest quartile of SHBG, adjusted for BMI and known diabetes risk factors]. The associations remained consistent within ethnic groups [RR, 0.19 (95% CI, 0.10-0.38) for blacks; RR, 0.17 (95% CI, 0.05-0.57) for Hispanics; and 0.13 (95% CI, 0.03-0.48) for Asians]. Adjustment for potential confounders, such as total testosterone (RR, 0.11; 95% CI, 0.07-0.19) or HOMA-IR (RR, 0.26; 95% CI, 0.14-0.48) did not alter the RR substantially. In addition, SHBG concentrations were significantly associated with risk of clinical diabetes across categories of hormone therapy use (never users: RR(per SD) = 0.42, 95% CI, 0.34-0.51; past users: RR(per SD) = 0.53;, 95% CI, 0.37-0.77; current users: RR(per SD) = 0.57; 95% CI, 0.46-0.69; P-interaction = 0.10). CONCLUSIONS In this prospective study of postmenopausal women, we observed a robust, inverse relationship between serum concentrations of SHBG and risk of clinical diabetes in American blacks, Hispanics, and Asians/Pacific Islanders. These associations appeared to be independent of sex hormone concentrations, adiposity, or insulin resistance.