Racial disparities in metabolism, central obesity, and sex hormone-bindingglobulin in postmenopausal women

Increased total and intraabdominal fat (LAF) obesity as well as other metab olic conditions associated with the insulin resistance syndrome (IRS) are r elated to low levels of sex hormone-binding globulin (SKBG) in young and ol der Caucasian (CAU) and young African-American (AA) women. We examined whet her postmenopausal AA women, a population with a high incidence of obesity and IRS despite low IAF, would have higher levels of circulating SHBG compa red with CAU women, and whether there would be negative relationships betwe en indexes of obesity and risk factors associated with IRS and SHBG levels. We measured body composition, SHBG, free testosterone, leptin, glucose tol erance, insulin, and lipoprotein lipids in 55 CAU (mean +/- SD, 59 +/- 7 yr ) and 35 AA (57 +/- 6 yr) sedentary women of comparable obesity (48% body f at, by dual energy x-ray absorptiometry). Compared with CAU women, AA women had larger waist (101 vs. 96 cm), larger fat mass (44.9 +/- 8.8 vs. 39.9 /- 8.1 kg), larger sc fat area (552 +/- 109 vs. 452 +/- 109 cm(2)), and low er IAF/SC ratio (0.28 +/- 0.12 vs. 0.38 +/- 0.15; P < 0.01), but similar wa ist to hip ratio (0.83). Both groups had similar SHBG (117 vs. 124 nmol/L) and free testosterone (3.7 vs. 3.4 pmol/L) levels, but AA women had a 35% h igher leptin, 34% higher fasting insulin, and 39% greater insulin response to a glucose load (P < 0.05) compared with CAU women. In CAU, but not AA, w omen SHBG correlated negatively with body mass index (r = -0.28; P < 0.05), waist (r = -0.36; P = 0.01), IAF (r = -0.34; P = 0.01), and insulin respon se to oral glucose (r = -0.37; P < 0.05) and positively with high density l ipoprotein cholesterol (r = 0.30; P = 0.03). The relationship between insul in area and SHBG in CAU women disappeared after adjusting for IAF, whereas the relationship between high density lipoprotein cholesterol and SHBG pers isted after adjusting for IAF, but not for fat mass. Leptin was positively related to fat mass (P < 0.05) in both groups, but it was related to insuli n only in the Caucasian women (P < 0.01). There was a racial difference in the slopes (P < 0.05) of the relationships of leptin to fat mass (P < 0.05) . Racial differences in leptin disappeared after adjustment for fasting ins ulin. These results suggest that the metabolic relationships between total and regional obesity, glucose, and lipid metabolism with SHBG in CAU women are different from those in postmenopausal obese AA women.