The relationship of sex hormones to hyperinsulinemia and hyperglycemia

Mexican-Americans, a high-risk population for non-insulin-dependent diabetes mellitus (NIDDM), have been previously reported to have decreased levels of sex-hormone-binding globulin (SHBG). We measured total testosterone, total estradiol and SHBG, glucose and insulin in premenopausal women (58 Mexican-Americans and 38 non-Hispanic whites) as part of the San Antonio Heart Study, a population-based study of cardiovascular risk factors. Although total estradiol and total testosterone were, in general, not correlated with metabolic variables, SHBG was negatively correlated with glucose and insulin. After adjustment for body mass index (BMI), ratio of waist-to-hip circumference (WHR) and ratio of subscapular-to-triceps skinfold (Centrality Index), SHBG was still significantly correlated with insulin concentrations (P < .001). Since Mexican-Americans were previously reported to be more hyperinsulinemic than non-Hispanic whites, we examined the effect of adjusting for SHBG on insulin levels in this small population. While unadjusted insulin concentrations in Mexican-Americans were higher than in non-Hispanic whites (354 μU/mL v 236 μU/mL, respectively, P = .009), adjustment for BMI, WHR, and centrality index reduced the ethnic difference in insulin levels considerably (P = .014). However, only after adjusting for SHBG as well, did the ethnic difference in insulin levels became nonsignificant. Our data suggest that alterations in sex hormones and SHBG in particular may be related to the hyperinsulinemia and the high rates of NIDDM in Mexican-Americans.