Increased total and intraabdominal fat (IAF)
obesity as well as other metabolic conditions associated with the
insulin resistance syndrome (IRS) are related to low levels of
sex hormone-binding globulin (SHBG) in young and older Caucasian (CAU) and young African-American (AA) women. We examined whether postmenopausal AA women, a population with a high incidence of
obesity and IRS despite low IAF, would have higher levels of circulating SHBG compared with CAU women, and whether there would be negative relationships between indexes of
obesity and risk factors associated with IRS and SHBG levels. We measured body composition, SHBG, free
testosterone,
leptin,
glucose tolerance,
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 fat, 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 lower IAF/SC ratio (0.28 +/- 0.12 vs. 0.38 +/- 0.15; P < 0.01), but similar waist 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% higher
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, women 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 response to oral
glucose (r = -0.37; P < 0.05) and positively with
high density lipoprotein cholesterol (r = 0.30; P = 0.03). The relationship between
insulin area and SHBG in CAU women disappeared after adjusting for IAF, whereas the relationship between
high density lipoprotein cholesterol and SHBG persisted 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
insulin 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
insulin. 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.