Inconvenient relationship of haemoglobin A1c level with endothelial function in type 2 diabetes in a cross-sectional study

Objective The aim of this study was to determine the relationship of haemoglobin A1c (HbA1c) level with flow-mediated vasodilation (FMD) and nitroglycerine-induced vasodilation (NID) in patients with type 2 diabetes. Design Cross-sectional study. Setting 22 university hospitals and affiliated clinics in Japan. Participants 1215 patients with type 2 diabetes including 349 patients not taking antidiabetic drugs. Measures We evaluated FMD and HbA1c level. All patients were divided into four groups based on HbA1c level: <6.5%, 6.5%-6.9%, 7.0%-7.9% and >= 8.0%. Results An inverted U-shaped pattern of association between HbA1c level and FMD was observed at the peak of HbA1c of about 7%. FMD was significantly smaller in the HbA1c <6.5% group than in the HbA1c 6.5%-6.9% group and HbA1c 7.0%-7.9% group (p<0.001 and p<0.001), and FMD values were similar in the HbA1c <6.5% group and HbA1c >= 8.0% group. There were no significant differences in NID values among the four groups. After adjustments for confounding factors, FMD was significantly smaller in the HbA1c <6.5% group than in the HbA1c 6.5%-6.9% and HbA1c 7.0%-7.9% group (p=0.002 and p=0.04). In patients not taking antidiabetic drugs, FMD was also significantly smaller in the HbA1c <6.5% group than in the HbA1c 6.5%-6.9% group and HbA1c 7.0%-7.9% group (p<0.001 and p=0.02), and there were no significant differences in NID values among the four groups. Conclusions These findings suggest that there is an inverted U-shaped pattern of association between FMD and HbA1c and that a low HbA1c level of

Automated summary

This study aimed to investigate the relationship between HbA1c levels and vascular function in patients with type 2 diabetes. Results showed an inverted U-shaped pattern of association between HbA1c levels and FMD, with FMD being significantly smaller in patients with low HbA1c levels. There were no significant differences in NID values among the groups.