Insulin Response In Relation To Insulin Sensitivity: An Appropriate β-Cell Response In Black South African Women

  1. Julia H. Goedecke, PhD (julia.goedecke{at}uct.ac.za)1,3,
  2. Joel A. Dave, MB, ChB, PhD2,
  3. Mirjam V. Faulenbach, MD4,
  4. Kristina M. Utzschneider, MD4,
  5. Estelle V. Lambert, PhD1,
  6. Sacha West, PhD1,
  7. Malcolm Collins, PhD1,3,
  8. Tommy Olsson, MD5,
  9. Brian R Walker, MD5,
  10. Jonathan R Seckl, MB, PhD5,
  11. Steven E. Kahn, MB, ChB4 and
  12. Naomi S. Levitt, MB, ChB2
  1. 1UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology and
  2. 2Endocrine Unit, Department of Medicine, University of Cape Town, South Africa
  3. 3South African Medical Research Council
  4. 4Division of Metabolism, Endocrinology and Nutrition, Department of Medicine, VA Puget Sound Health Care System and University of Washington, Seattle, WA, USA
  5. 5Department of Medicine, Umeå University, Sweden
  6. 6Endocrinology Unit, Centre for Cardiovascular Science, University of Edinburgh, Scotland

    Abstract

    Objective: To characterise differences in the acute insulin response to glucose (AIRg) relative to insulin sensitivity (SI) 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 body mass index. SI, AIRg and the disposition index (DI=AIRg × SI) were measured using a frequently sampled intravenous glucose tolerance test with Minimal Model analysis and similar measures using an oral glucose tolerance test (OGTT). Body composition was assessed by dual-energy X-ray absorptiometry and computerised tomography.

    Results: SI 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 AIRg significantly higher (1028±255 vs. 352±246 and 1968±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 to their white counterparts, respectively. DI, a marker of β-cell function, was not different between ethnic groups (3811±538 vs. 2966±518 and 3646±485 vs. 2353±518 ×10−5min, 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 in order to maintain normal glucose levels, suggesting an appropriate β-cell response for the level of insulin sensitivity.

    Footnotes

      • Received November 13, 2008.
      • Accepted January 30, 2009.

    This Article

    1. Published online before print February 5, 2009, doi: 10.2337/dc08-2048
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