INSULIN SENSITIVITY AND ABDOMINAL OBESITY IN AFRICAN-AMERICAN, HISPANIC, AND NON-HISPANIC WHITE MEN AND WOMEN THE INSULIN-RESISTANCE AND ATHEROSCLEROSIS STUDY

Increased abdominal obesity has been related to lower insulin sensitiv ity (S-I), independent of overall obesity, but it has been suggested t hat this relationship may be weaker in non-whites. In the Insulin Resi stance and Atherosclerosis Study (IRAS), S-I was estimated using a min imal model analysis of the frequently sampled intravenous glucose tole rance test in 1,625 men and women aged 40-69 years. Subjects included African-Americans, Hispanics, and non-Hispanic whites from Oakland and Los Angeles, CA, San Antonio, TX, and the San Luis Valley, CO. Minimu m waist circumference was significantly (P = 0.0001) associated with S -I after adjusting for age, sex, height, BMI, glucose tolerance status , ethnicity, and clinic. This relationship was significantly (P = 0.00 01) stronger in subjects with normal glucose tolerance (NGT) (beta = - 0.030, P 0.0001) than in those with impaired glucose tolerance (IGT) ( beta = -0.010, P = 0.02; NIDDM: beta = -0.013, P 0.0001). There were n o significant ethnic differences in effect size across the spectrum of glucose tolerance. Waist circumference was also positively related to fasting insulin, an indirect measure of insulin sensitivity, in NGT ( P = 0.0001), IGT (P = 0.0003), and NIDDM (P = 0.0002). The waist-fasti ng insulin relationship was significantly weaker in African-Americans, relative to non-Hispanic whites, in NGT and IGT (tests of statistical interaction: P = 0.04 and P = 0.02, respectively). In general, these patterns were similar in models specifying waist-to-hip ratio (WHR), r ather than waist circumference, as the independent variable. While som e ethnic variability exists, a negative relationship between abdominal obesity and insulin sensitivity was confirmed for all three ethnic gr oups across the spectrum of glucose tolerance.