Evidence for insulin resistance in black women from South Africa.
OBJECTIVE
The rate of glucose disposal was determined in 10 black and 10 white obese nondiabetic urban women from South Africa to assess insulin resistance.


METHODS
Euglycemic hyperinsulinemic clamp and body composition analysis.


RESULTS
Age, body mass index (BMI), anthropometric measurements and body composition were similar in both groups of women. A five-level computed tomography (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 cm2), but less visceral fat in black obese women (90 +/- 3.0 vs 121 +/- 3.1 cm2; P< 0.05). Black obese women had higher fasting free fatty acid (997 +/- 69 vs 678 +/- 93 micromol/l; P < 0.05) and lactate concentrations (1,462 +/- 94 vs 1,038 +/- 39 micromol/l; P < 0.05), but lower fasting insulin levels (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). The mean glucose disposal rate (M) and disposal expressed as glucose sensitivity 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 x min(-1)/pmol/1 x 1,000; P < 0.01). Only black obese women showed a significant decrease in C-peptide levels during the clamp (2.9 +/- 0.22 vs 1.2 +/- 0.12 nmol/l; P<0.001). During the 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 1,300 +/- 53 micromol/l; P< 0.05).


CONCLUSIONS
Black obese women demonstrate a higher degree of insulin resistance, despite less visceral fat and a higher HDL: total-cholesterol ratio. In addition, endogenous beta-cell secretory function in black obese women appears to be more sensitive to the suppressive effect of exogenous insulin administration. The significant increase in lactate levels in white obese women confirms that they are more insulin sensitive.
van der Merwe
M T
MT
Carbohydrate and Lipid Metabolism Research Group, University of Witwatersrand Medical School, Johannesburg, South Africa. 014jhp@chiron.wits.ac.za
Crowther
N J
NJ
Schlaphoff
G P
GP
Gray
I P
IP
Joffe
B I
BI
Lönnroth
P N
PN
D000328:Adult; D001741:Black or African American / Q000706:statistics & numerical data*; D044383:Black People; D001786:Blood Glucose / Q000378:metabolism*; D001823:Body Composition; D015992:Body Mass Index; D002096:C-Peptide / Q000097:blood; D005260:Female; D015309:Glucose Clamp Technique; D006801:Humans; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance; D007773:Lactates / Q000097:blood; D008055:Lipids / Q000097:blood*; D009765:Obesity / Q000208:ethnology / Q000378:metabolism*; D015995:Prevalence; D013019:South Africa / Q000453:epidemiology; D044465:White People / Q000706:statistics & numerical data
D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin; D007773:Lactates; D008055:Lipids