Serum gamma-glutamyltransferase levels are related to insulin sensitivity and secretion in subjects with abnormal glucose regulation

BACKGROUND: To test the association between gamma-glutamyltransferase level and glucose regulation. METHODS: We performed a cross-sectional analysis of 500 subjects [199 men/301 women, age 47 +/- 11 years, body mass index (BMI) 28.6 +/- 5.5 kg/m(2)] referred to Diabetes Clinics because of potential risk of type 2 diabetes mellitus (T2DM). RESULTS: The prevalence of all glucose intolerance categories was higher in the top quartile of gamma-glutamyltransferase than in the first. Subjects with normal glucose tolerance showed lower gamma-glutamyltransferase levels compared with those with impaired glucose tolerance (IGT), impaired fasting glucose (IFG)+ IGT and T2DM (ANOVA, p < 0.0001), but not those with IFG. Homeostasis model assessment-insulin resistance (HOMA-IR) increased with increasing levels of gamma-glutamyltransferase, while the insulinogenic index/HOMA-IR ratio decreased. In an age- and sex-adjusted analysis, the top gamma-glutamyltransferase quartile was independently associated with IFG + IGT [odds ratio (OR) 2.41; 95% confidence interval (CI): 1.13-5.15] and T2DM (OR 2.77; 95% CI: 1.47-5.22). After further adjustment for BMI, alcohol intake, family history of diabetes, cigarette smoking and physical activity, the top quartile of gamma-glutamyltransferase remained an independent predictor of IFG + IGT (OR 2.62; 95% CI: 1.13-6.07) and T2DM (OR 2.39; 95% CI: 1.20-4.76). Only when transaminases and HOMA-IR have been added to the model, the top quartile of gamma-glutamyltransferase resulted no more independently associated to IFG + IGT or T2DM. CONCLUSIONS: Gamma-glutamyltransferase is closely related to insulin resistance, reduced beta-cell function and deterioration of glucose tolerance