"In persons with diabetes, we know that traditional cardiovascular risk factors, such as hypertension and high cholesterol, should be treated aggressively. Our results also suggest that improving blood-glucose control may further reduce heart disease risk," said Elizabeth Selvin, PhD, MPH, lead author of the study and a postdoctoral fellow in the Bloomberg School of Public Health's Department of Epidemiology. "For non-diabetics, lifestyle modifications, such as increased physical activity, weight loss and eating a healthful, low-glycemic, index diet rich in fiber, fruit and vegetables, may not only help prevent diabetes, but also reduce the risk of heart disease," she said.
The researchers used data from the Atherosclerosis Risk in Communities Study (ARIC), a community-based cohort of almost 16,000 people from four states--North Carolina, Mississippi, Maryland and Minnesota. HbA1c levels were taken from ARIC study participants during clinical examinations in 1990-1992. ARIC researchers tracked study participants for 10-12 years to acquire coronary heart disease events, hospitalizations and deaths.
In participants with diabetes, the researchers found a graded association between HbA1c and increasing coronary heart disease risk. Each 1-percentage-point increase in HbA1c level was associated with a 14 percent increase in heart disease risk. According to the study authors, the current target for "good" glycemic control established by the American Diabetes Association is an HbA1c value less than 7 percent. However, the researchers' analyses suggest that heart disease risk begins to increase at values even below 7 percent.
They found that those study participants without diabetes but who had "high normal" HbA1c levels (approximately 5 percent to 6 percent) were at an increased heart disease risk, even after accounting for other factors such as age, cholesterol level, blood pressure, body mass index and smoking. Non-diabetic persons with HbA1c levels of 6 percent or higher had almost a two-fold greater heart disease risk compared to persons with an HbA1c level below 4.6 percent.
"There are large, on-going clinical trials which should definitively answer the question of the effectiveness of blood glucose-lowering medications in decreasing cardiovascular risk in persons with type-2 diabetes. But our results suggest we should also be concerned about elevated blood sugar levels in non-diabetics as well. An important next step is to investigate strategies for lowering HbA1c in persons without diabetes," said Selvin.
Co-authors of the study are Elizabeth Selvin, Josef Coresh, Sherita H. Golden, Frederick L. Brancati, Aaron R. Folsom and Michael W. Steffes.
Archives of Internal Medicine