Age‐Related Changes in Insulin Sensitivity and β‐Cell Function Among European‐American and African‐American Women

Abstract

Type 2 diabetes (T2D) is more prevalent among African‐American (AA) than European‐American (EA) women for reasons that are unknown. Ethnic differences in physiological processes related to insulin sensitivity (S_I) and secretion, and age‐related changes in these processes, may play a role. The purpose of this study was to identify ethnicity‐ and age‐related differences in S_I and β‐cell responsivity among AA and EA females, and to determine whether these differences are independent of body composition and fat distribution. Healthy, normoglycemic females aged 7–12 years (n = 62), 18–32 years (n = 57), and 40–70 years (n = 49) were recruited for entry into this study. Following an overnight fast, S_I, intravenous glucose tolerance (Kg), acute C‐peptide secretion (X0), and basal, first‐phase, second‐phase, and total β‐cell responsivity to glucose (PhiB, Phi1, Phi2, and Phi_TOT, respectively) were measured by an intravenous glucose tolerance test. Total % body fat was assessed by dual‐energy X‐ray absorptiometry, and intra‐abdominal adiposity (IAAT) by computed tomography. Main effects of age group and ethnicity were measured with analysis of covariance, adjusting for % fat, IAAT, and S_I as indicated. AA had lower S_I, and higher Kg, X0, Phi1, and Phi_TOT (P < 0.05), which remained after adjustment for % fat and IAAT. Greater X0, Phi1, and Phi_TOT among AA were independent of S_I. Advancing age was associated with greater Phi2 among both EA and AA. To conclude, inherent ethnic differences in β‐cell function exist independently of adiposity and S_I. Future research should examine whether ethnic differences in β‐cell physiology contribute to disparities in T2D risk.