One hundred eighty-two nondiabetic African-Americans (74 Men, 108 Women) have participated. The age range of the participants is 20 to 50 years. This sample of African Americans can be considered representative because the prevalence of obesity (43%), glucose intolerance (22%) and hypertension (21%) is similar to NHANES data. NHANES stands for National Health and Nutrition Examination and is a nationwide survey with thousands of participants. The participants range from very lean to very obese. The mean body mass index of participants is 30.6 kg/m2 (range 18.5 54.7). Body mass index is a mathematical method used to correct weight for height. Due to the broad range of body mass index in the participants it is possible to make conclusions about the relationship of body size to insulin resistance. We have found in African American men that a waist circumference of 102 cm in men predicts both insulin resistance and obesity. Therefore we are completely in agreement with the National Cholesterol Education Program values for whites. However, in African American women we found that a waist circumference of 98 cm predicted both insulin resistance and obesity. Based on investigations in white women the National Cholesterol Education Program recommends that a waist circumference threshold of 88 cm be used. Therefore our work demonstrates the need for ethnic specific modifications of guidelines in women. Elevated TG and low HDL are considered lipid hallmarks of insulin resistance. However while elevated TG is a marker of insulin resistance in whites, we have shown that TG is not a marker of insulin resistance in African Americans. The investigation of the relationship of TG to insulin resistance has become such an important component of this research, that the cohort of African Americans participating in this protocol are now known as TARA for Triglyceride and Cardiovascular Risk in African Americans. Results from TARA were so impressive that the hypothesis that TG was not a marker of insulin resistance in African Americans was tested in NHANES data from 1999-2001. In this nationwide data set of whites, African Americans and Mexican Americans, the fact that TG was not a marker of insulin resistance was confirmed. However, TG was a marker of insulin resistance in whites and Mexican Americans. Again this demonstrates the need for ethnic specific guidelines. To develop an index of free fatty acid sensitivity to insulin, we are working with mathematicians. The modeling is underway. The modeling of the influence of insulin on glucose levels was done in the nineteen eighties by Richard N. Bergman and colleagues. Because of the multiplicity of hormones that affect free fatty acid levels as well as the much wider range of biological variation in free fatty acids than glucose, achieving a model of the effect of insulin on free fatty acids is an even greater challenge. To achieve a model 150 participants in TARA have had frequently sampled intravenous glucose tests with glucose, insulin and free fatty acids levels determined at 36 timepoints in a 3 to 6 hour period. The complex multicompartment modeling is underway. In the last year over 50 Black Africans living in the Washington DC metropolitan area have been recruited. We are learning that Black Africans living in the United States matched by age, sex and BMI are less metabolically healthy in terms of insulin resistance, glucose tolerance and lipid profile than African Americans. This part of the cohort will be known as BART for Black Africans and Risk regarding TG levels and other Metabolic Factors. Analyses of the data is underway, but one reason for the lower metabolic health in BA comparing to AA may be the relatively rapid weight BA experience once emigration to the United States occurs.
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