BACKGROUND:
Recent prospective studies have shown a strong inverse association between sex hormone-binding globulin (SHBG) levels and risk of clinical diabetes in Whites. However, it remains unknown whether this relation extends to other racial/ethnic populations.
METHODS:
We evaluated the association between baseline levels of SHBG and risk of clinical diabetes in the Women’s Health Initiative Observational Study. Over a median follow-up of 5.9 years, 542 postmenopausal women developed clinical diabetes (338 Blacks, 128 Hispanics, 76 Asians) and were matched to 1,110 controls (707 Blacks, 249 Hispanics, 154 Asians). To complement our protein-level findings, we also genotyped 5
SHBG
polymorphisms. We performed Mendelian randomization analysis to assess the potential causal relation between SHBG levels and risk of clinical diabetes.
RESULTS:
Overall, higher levels of SHBG at baseline were associated with a significantly lower risk of clinical diabetes (Relative risk [RR]=0.24, 95% confidence interval [CI]=0.15-0.39 for highest versus lowest quartile of SHBG, adjusted for BMI and other known diabetes risk factors). The associations remained consistent across ethnic groups (p-for-heterogeneity=0.72): RR=0.29 (95%CI=0.16-0.54) for Blacks, RR=0.26 (95%CI=0.09-0.74) for Hispanics, and RR=0.32 (95%CI=0.06-1.73) for Asians, comparing highest to lowest quartiles of SHBG. In addition,
SHBG
polymorphisms affected diabetes risk proportional to serum SHBG levels. Mendelian randomization analysis confirmed the significant direct effect of SHBG on diabetes development (p=0.03).
CONCLUSIONS:
In this prospective cohort of postmenopausal women, we observed a robust, inverse relation between serum levels of SHBG and clinical diabetes risk in American Blacks, Hispanics, and Asian/Pacific Islanders. Genetic variants associated with SHBG levels demonstrated a similar relationship, providing support for a causal role of SHBG in the pathogenesis of type 2 diabetes.
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