Effect of Serum Gamma-Glutamyltransferase and Obesity on the Risk of Dyslipidemia and Poor Glycemic Control in Type 2 Diabetic Patients: Cross-Sectional Findings from the Verona Diabetes Study

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To the Editor:

We read with interest the article by Lim et al. (1) regarding a strong interaction between serum gamma-glutamyltransferase (GGT) activity and body mass index (BMI) and their effect on the risk of prevalent diabetes. The authors found that BMI is associated with prevalent diabetes only among individuals with high-normal GGT, suggesting that GGT determination can be useful in clinical settings for identifying individuals at high risk for diabetes.

Given the scientific and clinical importance of an interaction between obesity and GGT in predicting diabetes, we investigated possible interactions between BMI and GGT in predicting poor glycemic control and common comorbidities of diabetes. Therefore, we assessed whether the association of BMI with hypertension, dyslipidemia, and poor glycemic control differed according to serum GGT activities in a type 2 diabetic population.

Study participants were enrolled in the Verona Diabetes Study, a prospective observational study designed primarily to evaluate associations between type 2 diabetes and incidence of cardiovascular complications (2). In this analysis, we included 2929 type 2 diabetic outpatients [56% males; mean (SD) age 68 (10) years] who regularly attended our clinic and who had complete data for analysis. Fasting serum GGT and lipid values were determined by standard laboratory procedures (Roche Diagnostics). Hemoglobin A1c was measured with an HPLC analyzer (Bio-Rad Diamat); the upper limit of the reference interval for the laboratory was 5.9%. LDL-cholesterol was calculated with the Friedewald’s equation. Patients were considered to have hypertension if they had blood pressure values ≥140/90 mmHg or were on treatment, and to have atherogenic dyslipidemia if they had high triglycerides (>1.7 mmol/L) and/or low HDL cholesterol (<1.04 mmol/L) or were on treatment(3). Poor glycemic control was defined as hemoglobin A1c >7%(3). We used separate multivariable logistic regression analyses to examine the interaction relationships with hypertension, dyslipidemia, or glycemic control as the dependent variables, predicted from BMI (categorized as <25, 25–29.9, 30–34.9, and ≥35 kg/m²) within the quartiles of GGT (<16, 16–25, 26–43, and ≥44 U/L). Adjusting variables were sex, age, and diabetes duration and treatment (diet, oral agents, or insulin).