Gender differences in insulin-stimulated glucose utilization among African-Americans

The purpose of this study was to determine whether there are gender differences in plasma insulin levels or insulin resistance in young adult African-Americans. Male (n = 53) and female (n = 45) subjects (age 23 to 28 years) included normotensives (N, blood pressure [BP] < 135/85 mm Hg) and borderline hypertensives (BH, BP > 135/85 mm Hg). Plasma insulin concentration was measured during an oral glucose tolerance test (OGTT) in all subjects. In 50 cases, insulin clamps were performed. Plasma estradiol and free testosterone were analyzed in a subsample (n = 15) of women. Data were analyzed for BP and gender groups by two-way ANOVA. Compared to men, women in each BP group had higher plasma insulin: glucose ratios (P < .01) and sums of insulin on OGTT (P < .02). The insulin clamp data also demonstrated significantly lower insulin-stimulated glucose utilization (M) in women compared to men in each BP group (N males 7.28 +/- 0.72 v N females 4.94 +/- 1.2 mg/kg-min; BH males 5.28 +/- .56 v BH females 2.59 +/- 0.50 mg/kg-min; P < .004 for gender differences). Analysis of the sex hormone data found a significant correlation in the ratio of free testosterone/estradiol (T/E) with plasma glucose, insulin, insulin/glucose, and systolic BP (P < .05), and no correlation of T/E with body mass index or triceps skinfold thickness. These data indicate that there are significant gender differences in plasma insulin levels and in insulin sensitivity in African-Americans. The relationship of plasma insulin to sex hormones suggests that in females, hyperinsulinemia cosegregates with increased androgenicity.