Aims Although many studies have reported an association between serum γ-glutamyltransferase (GGT) and cardiovascular risk factors, the mechanism of this relationship has not been clarified.
Methods The medical records of 29 959 subjects (age, median 48, range 14–90 years; 16 706 men, 13 253 women) who visited the Center for Health Promotion at Samsung Medical Center for a medical check-up between January 2001 and December 2003, were investigated. Subjects with hepatic enzyme/GGT concentrations higher than three times the upper limit of the reference range, a positive test for hepatitis C virus antibody, a positive test for hepatitis B virus surface antigen, currently taking anti-diabetic/anti-hypertensive/anti-lipid medication, or a white blood cell (WBC) count higher than 10 000 cells/ml, were excluded. The subjects of each gender were classified into five groups according to their serum GGT concentrations, into quartiles of the normal range of GGT (groups 1, 2, 3 and 4) and into a group with elevated GGT (group 5).
Results As the group number increased (group 1 → 5), the frequencies of all of the following increased: (i) diabetes and impaired fasting glucose (IFG); (ii) hypertension, obesity (body mass index ≥ 27 kg/m2), dyslipidaemia (LDL-cholesterol ≥ 4.1 mmol/l and/or triglyceride ≥ 2.46 mmol/l, or HDL-cholesterol < 1.16 mmol/l); (iii) metabolic syndrome. Moreover, these significant relationships between GGT concentrations within its normal range and the presence of diabetes/IFG, hypertension, obesity, dyslipidaemia, and metabolic syndrome persisted after adjusting for several clinical and biochemical variables and for the presence of fatty liver based on ultrasonographic findings. Odds ratios (95% CI) for group 4 (highest quartile of normal range of GGT) vs. group 1 (lowest quartile of normal range of GGT); the referent group, were 3.16 (2.15–4.65) for diabetes, 2.24 (1.73–2.90) for IFG, 1.93 (1.59–2.33) for obesity, 1.38 (1.23–1.55) for dyslipidaemia and 2.88 (2.28–3.65) for metabolic syndrome in men. In women, the odds ratios were 2.72 (1.34–5.52), 3.67 (2.26–5.97), 2.10 (1.61–2.74), 1.80 (1.58–2.04) and 3.57 (2.52–5.07), respectively.
Conclusions Our data show that, even within its normal range, serum GGT concentrations are closely associated with the presence of diabetes and cardiovascular risk factors, and that these associations are independent of a fatty liver by ultrasonography.