Obesity, Insulin Resistance, and the Metabolic Syndrome Determinants of Endothelial Dysfunction in Whites and Blacks

Background—Insulin resistance is strongly associated with obesity and other components of the metabolic syndrome (MS). The relative importance of these components in the determination of endothelial function is unknown. Furthermore, there is conflicting evidence about whether ethnic differences exist in the relative importance of these components in regard to other cardiovascular outcomes. We evaluated the contributions of insulin resistance, obesity, and the other components of the MS to impaired endothelial function. Methods and Results—The relationships of the MS components (as defined according the National Cholesterol Education Program) and insulin resistance (estimated using the homeostasis model) with endothelium-dependent vasodilation were examined in 42 white and 55 black subjects. Endothelium-dependent vasodilation was assessed as the increment in leg blood flow (measured by thermodilution) after exposure to methacholine chloride. Waist circumference, glucose, blood pressure, and insulin resistance distributions did not differ between ethnic groups; blacks in our sample had higher HDL cholesterol (1.31 versus 1.09 mmol/L; P0.001) and lower triglyceride levels (1.01 versus 1.37 mmol/L; P0.005) than white subjects. In the absence of the MS, black subjects exhibited reduced endothelium-dependent vasodilation compared with white subjects (P0.005), and both groups demonstrated significantly worse endothelial function when the MS was present (maximal increase in leg blood flow: blacks: 1079 % MS absent, 5316 % MS present; whites