Race Differences in the Association of Oxidative Stress With Insulin Sensitivity in African‐ and European‐American Women

Excessive metabolism of glucose and/or fatty acids may impair insulin signaling by increasing oxidative stress. The objective of this study was to examine the association between insulin sensitivity and protein carbonyls, a systemic marker of oxidative stress, in healthy, nondiabetic women, and to determine if the relationship differed with race. Subjects were 25 African‐Americans (AA, BMI 28.4 ± 6.2 kg/m 2 , range 18.8–42.6 kg/m 2 ; age 33.1 ± 13.5 years, range 18–58 years) and 28 European‐Americans (EA, BMI 26.2 ± 5.9 kg/m 2 , range 18.7–48.4 kg/m 2 ; age 31.6 ± 12.4 years, range 19–58 years). Insulin sensitivity was determined using an intravenous glucose tolerance test incorporating [6,6‐ 2 H 2 ]‐glucose, and a two‐compartment mathematical model. Multiple linear regression results indicated that insulin sensitivity was inversely associated with protein carbonyls in AA (standardized regression coefficient −0.47, P < 0.05) but not EA (0.01, P = 0.945), after adjusting for %body fat. In contrast, %body fat was significantly and positively associated with insulin sensitivity in EA (−0.54, P < 0.01) but not AA (−0.24, P = 0.196). Protein carbonyls were associated with free fatty acids (FFA) in AA ( r = 0.58, P < 0.01) but not EA ( r = −0.11, P = 0.59). When subjects were divided based on median levels of fasting glucose and FFA, those with higher glucose/FFA concentrations had a significantly greater concentration of circulating protein carbonyls compared to those with lower glucose/FFA concentrations ( P < 0.05). These results suggest that oxidative stress independently contributes to insulin sensitivity among AA women. Further, this association in AA may be mediated by circulating FFA and/or glucose.