Relationship between Hemoglobin A1c Level and Flow-mediated Vasodilation in Patients with Type 2 Diabetes Mellitus Receiving Antidiabetic Drugs.

AIMS/INTRODUCTION Diabetes mellitus (DM) is associated with endothelial dysfunction. However, it is still controversial whether antidiabetic drug treatment affects endothelial function. The purpose of this study was to evaluate the relationships of hemoglobin A1c (HbA1c) level with flow-mediated vasodilation (FMD) and nitroglycerine-induced vasodilation (NID) in patients with type 2 DM who are receiving antidiabetic drugs. MATERIALS AND METHODS We measured FMD in 866 patients with type 2 DM who were receiving antidiabetic drugs (625 men and 241 women; mean age: 62±10 years). The patients were divided into four groups according to HbA1c levels: <6.5%, 6.5%-6.9%, 7.0%-7.9%, and ≥8.0%. RESULTS There was an inverted U-shaped pattern of the association of HbA1c level with FMD at an HbA1c level of about 7% of the peak of FMD in patients with type 2 DM who were receiving antidiabetic drugs. FMD was significantly smaller in the HbA1c level of <6.5% group than in the HbA1c level of 6.5%-6.9% group and HbA1c level of 7.0%-7.9% group (p<0.001 and p<0.001, respectively). FMD values were similar in the HbA1c level of <6.5% group and HbA1c level of ≥8.0% group (p=0.10). There were no significant differences in NID among the four groups (p=0.98). CONCLUSIONS These findings suggest that a low HbA1c level of <6.5% as well as a high HbA1c level of ≥8.0% is associated with endothelial dysfunction in patients with type 2 DM who are receiving antidiabetic drugs and that vascular smooth muscle function is similar in such patients regardless of the HbA1c level.