Background Insulin resistance is strongly associated with obesity and other components of the metabolic syndrome. The relative importance of these components in the determination of endothelial function is unknown. Furthermore, there is conflicting evidence whether there are ethnic differences in the relative importance of these components in regard to other cardiovascular outcomes. We evaluated the relative contributions of insulin resistance, obesity, and the other components of the metabolic syndrome to impaired endothelial function.
Methods and Results We evaluated studies in 52 Caucasian and 76 African American subjects. African American subjects exhibited reduced endothelium-dependent vasodilation compared to Caucasian subjects (p = 0.03), and both groups demonstrated significantly worse endothelial function when the metabolic syndrome was present (p = 0.0004). In both groups, impaired endothelial function was associated with the presence of 3 or more metabolic syndrome components. By multivariable analysis waist circumference, systolic blood pressure, and triglyceride levels were associated with impaired endothelium-dependent vasodilation (p<0.0001). Waist circumference was no longer significantly associated after adding insulin resistance (HOMA-IR) to the modeling. The relative importance of these components differed by ethnic subgroup. In African American subjects, blood pressure was the dominant correlate of endothelial dysfunction, while insulin resistance was dominant among Caucasian subjects.
Conclusions These findings suggest that there are ethnic differences in vascular biology as it relates to endothelium-dependent vasodilation, and may imply different benefits from treatments targeting blood pressure or insulin resistance in different ethnic groups.