In Chinese patients with diabetes, having hemoglobin A1c (HbA1c) levels that are too high or too low may be associated with a greater risk of cardiovascular disease and death, according to a research letter published Jan. 25 in the Journal of the American College of Cardiology.

In this population-based retrospective cohort study, Eric Yuk Fai Wan, MSc, CStat, of the University of Hong Kong, and colleagues examined 117,389 adult Chinese patients with type 2 diabetes without any history of cardiovascular disease. After a median follow-up of 54.5 to 58.5 months, a J-shaped curvilinear relationship was observed between HbA1c levels and cardiovascular disease incidence, all-cause mortality and other outcomes. An HbA1c range of ≥7.0 percent to <7.5 percent had the lowest risk of new cardiovascular disease, coronary heart disease, stroke, heart failure, all-cause mortality and cardiovascular disease-related mortality. By comparison, an HbA1c <6.5 percent or ≥8.0 percent was associated with a significantly higher incidence of cardiovascular disease and all-cause mortality.

The authors conclude that this relationship may be related to the effects of severe hypoglycemia, but it remains unclear why low levels of HbA1c are associated with a higher risk of cardiovascular disease and all-cause mortality.

“This retrospective cohort analysis by Wan and co-authors is an important contribution to our understanding of the relationship between HbA1c, cardiovascular risk and mortality,” says Laurence S. Sperling, MD, FACC, chair of ACC’s Cardiometabolic Disease Work Group. “This was a well done analysis adjusting for multiple covariates and the authors fairly acknowledged the study limitations. This data supports prior observational data that there may be an optimal range of HbA1C (potentially 6.5-7.5).”

Keywords: Cardiovascular Diseases, Cohort Studies, Coronary Artery Disease, Coronary Disease, Follow-Up Studies, Heart Failure, Glycated Hemoglobin A, Hypoglycemia, Incidence, Retrospective Studies, Risk Factors, Stroke, Diabetes Mellitus, Metabolic Syndrome

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