Objective: To analyse the associations between serum gamma-glutamyl transpeptidase activity (GTP) and the components of the metabolic syndrome.
Design: Cross-sectional, observational study of hypertensive patients and controls.
Setting: The participating subjects visited the research laboratory of the Department of Internal Medicine, University of Oulu, Oulu, Finland.
Subjects: A total of 1045 Caucasians, 40-59 years of age, consisting of 261 drug-treated hypertensive men, 258 drug-treated hypertensive women and 526 age- and sex-matched controls.
Main outcome measures: The associations between GTP and the cardiovascular risk factors were analysed through multiple regression and logistic methods and by GTP tertiles. The independent effect of GTP on different insulin measures, calculated from the values of 2 h of oral glucose tolerance test, was estimated after concurrent adjustment for age, obesity and alcohol consumption.
Results: GTP correlated highly significantly with the components of the metabolic syndrome. The correlation coefficient were 0.33 between GTP and body mass index, 0. 25 between GTP and systolic blood pressure in control men (P = 0. 0001), 0.39 between GTP and triglycerides, and 0.32 between GTP and fasting insulin in hypertensive women (P = 0.0001). The association between GTP and blood pressure remained significant only at upright measurements in controls. All insulin measures had a significant positive association with increasing GTP tertiles in all the study groups (e.g. fasting insulin 8.1 mU L-1 in the lowest and 11.0 mU L-1in the highest tertile in control women, P = 0.0001), with the exception of fasting insulin in control men. In a pooled logistic analysis after adjustment for age, body mass index, alcohol consumption and gender, the independent predictors of the metabolic syndrome were body mass index, uric acid, total cholesterol and GTP (for log-transformed GTP odds ratio 4.0, 95% CI: 2.80-5.69).
Conclusions: There are significant associations between GTP and the components of the metabolic syndrome. Elevated levels of GTP may not always indicate increased alcohol consumption, but may also suggest the existence of the metabolic syndrome with its subsequent deleterious consequences.