Insulin Response in Relation to Insulin Sensitivity: An appropriate β-cell response in black South African women

OBJECTIVE: The purpose of this study was to characterize differences in the acute insulin response to glucose (AIR(g)) relative to insulin sensitivity (S(I)) in black and white premenopausal normoglycemic South African women matched for body fatness. RESEARCH DESIGN AND METHODS: Cross-sectional analysis including 57 black and white South African women matched for BMI, S(I), AIR(g), and the disposition index (AIR(g) × S(I)) were performed using a frequently sampled intravenous glucose tolerance test with minimal model analysis, and similar measures were analyzed using an oral glucose tolerance test (OGTT). Body composition was assessed by dual-energy X-ray absorptiometry and computed tomography. RESULTS: S(I) was significantly lower (4.4 ± 0.8 vs. 9.4 ± 0.8 and 2.9 ± 0.8 vs. 6.0 ± 0. 8 × 10(−5) min(−1)/[pmol/l], P < 0.001) and AIR(g) was significantly higher (1,028 ± 255 vs. 352 ± 246 and 1,968 ± 229 vs. 469 ± 246 pmol/l, P < 0.001), despite similar body fatness (30.9 ± 1.4 vs. 29.7 ± 1.3 and 46.8 ± 1.2 vs. 44.4 ± 1.3%) in the normal-weight and obese black women compared with their white counterparts, respectively. Disposition index, a marker of β-cell function, was not different between ethnic groups (3,811 ± 538 vs. 2,966 ± 518 and 3,646 ± 485 vs. 2,353 ± 518 × 10(−5) min, P = 0.10). Similar results were obtained for the OGTT-derived measures. CONCLUSIONS: Black South African women are more insulin resistant than their white counterparts but compensate by increasing their insulin response to maintain normal glucose levels, suggesting an appropriate β-cell response for the level of insulin sensitivity.