Abstract
Intravenous glucose tolerance tests have demonstrated lower whole-body insulin sensitivity (SI) among African Americans (AA) compared with European Americans (EA). Whole-body SI represents both insulin-stimulated glucose disposal, primarily by skeletal muscle, and insulin's suppression of endogenous glucose production (EGP) by liver. A mathematical model was recently introduced that allows for distinction between disposal and hepatic SI. The purpose of this study was to examine specific indexes of SI among AA and EA women to determine whether lower whole-body SI in AA may be attributed to insulin action at muscle, liver, or both. Participants were 53 nondiabetic, premenopausal AA and EA women. Profiles of EGP and indexes of Disposal SI and Hepatic SI were calculated by mathematical modeling and incorporation of a stable isotope tracer ([6,6-2H2]glucose) into the intravenous glucose tolerance test. Body composition was assessed by dual-energy x-ray absorptiometry. After adjustment for percentage fat, both Disposal SI and Hepatic SI were lower among AA (P = .009 for both). Time profiles for serum insulin and EGP revealed higher peak insulin response and corresponding lower EGP among AA women compared with EA. Indexes from a recently introduced mathematical model suggest that lower whole-body SI among nondiabetic AA women is due to both hepatic and peripheral components. Despite lower Hepatic SI, AA displayed lower EGP, resulting from higher postchallenge insulin levels. Future research is needed to determine the physiological basis of lower insulin sensitivity among AA and its implications for type 2 diabetes mellitus risk.
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