Evidence for insulin resistance in black women from South Africa

OBJECTIVE: The rate of glucose disposal was determined in 10 black and 10 w hite obese nondiabetic urban women from South Africa to assess insulin resi stance. DESIGN AND METHODS: Euglycemic hyperinsulinemic clamp and body composition analysis, RESULTS: Age, body mass index (BMI), anthropometric measurements and body c omposition were similar in both groups of women. A five-level computed tomo graphy (CT) scan showed a similar mean subcutaneous fat mass in both groups of women (black obese women 555 +/- 9.0 vs white obese women 532 +/- 6.0 c m(2)), but less visceral fat in black obese women (90 +/- 3.0 vs 121 +/- 3. 1 cm(2); P < 0.05). Black obese women had higher fasting free fatty acid (9 97 +/- 69 vs 678 +/- 93 mu mol/l; P < 0.05) and lactate concentrations (146 2 +/- 94 vs 1038 +/- 39 mu mol/l; P < 0.05), but lower fasting insulin leve ls (87 +/- 12 vs 155 +/- 9 pmol/l: P < 0.001). Black obese women also had a more favorable HDL: total cholesterol ratio (30.5% vs 23.0%; P < 0.04). Th e mean glucose disposal rate (M) and disposal expressed as glucose sensitiv ity index (M/I) were reduced in the black obese women vs white obese women (M: 7.1 +/- 0.8 vs 13.7 +/- 1.0 mmol/kg . min(-1) x 100; P < 0.01. and M/I: 0.12 +/- 0.01 vs 0.24 +/- 0.02 mmol/kg . min(-1)/pmol/l x 1000; P < 0.01). Only black obese women showed a significant decrease in C-peptide levels d uring the clamp (2.9 +/- 0.22 vs 1.2 +/- 0.12 nmol/l; P < 0.001), During th e euglycemic period, the black obese women had higher lactate levels at all time points, but only the white obese women had increased lactate levels ( 918 +/- 66 to 1300 +/- 53 mu mol/l; P < 0.05), CONCLUSION: Black obese women demonstrate a higher degree of insulin resist ance, despite less visceral fat and a higher HDL: total-cholesterol ratio. In addition, endogenous beta-cell secretory function in black obese women a ppears to be more sensitive to the suppressive effect of exogenous insulin administration. The significant increase in lactate levels in white obese w omen confirms that they are more insulin sensitive.