Racial differences in peripheral insulin sensitivity and mitochondrial capacity in the absence of obesity

Abstract

Context: African-American women (AAW) have an increased risk of developing type 2 diabetes compared with Caucasian women (CW). Lower insulin sensitivity has been reported in AAW, but the reasons for this racial difference and the contributions of liver versus skeletal muscle are incompletely understood. Objective: We tested the hypothesis that young, nonobese AAW manifest lower insulin sensitivity specific to skeletal muscle, not liver, and is accompanied by lower skeletal muscle mitochondrial oxidative capacity. Copyright © 2014 by the Endocrine Society. Participants and Main Outcome Measures: Twenty-two nonobese (body mass index 22.7± 3.1 kg/m2) AAW and 22 matched CW (body mass index 22.7± 3.1 kg/m2) underwent characterization of body composition, objectively assessed habitual physical activity, and insulin sensitivity with euglycemic clamps and stable-isotope tracers. Skeletal muscle biopsies were performed for lipid content, fiber typing, and mitochondrial measurements. Results: Peripheral insulin sensitivity was26%lower inAAW(P < .05). Conclusion: When compared with CW, AAW have similar hepatic insulin sensitivity but a muscle phenotype characterized by both lower insulin sensitivity and lower mitochondrial oxidative capacity. These observations occur in the absence of obesityandare not explained by physical activity. The only factor associated with lower insulin sensitivity in AAW was mitochondrial oxidative capacity. Because exercise training improves both mitochondrial capacity and insulin sensitivity, we suggest that it may be of particular benefit as a strategy for diabetes prevention in AAW.