Cardiovascular disease accounts for more than 75% of all deaths among people with diabetes mellitus. Over time, high blood sugar levels wreak havoc on the body, causing many complications, including kidney failure , blindness, nerve damage, and cardiovascular disease.

Research has shown that with diet, exercise, and medications to keep blood sugar levels within a near normal range, it is possible to delay the onset of small vessel diseases such as kidney failure, blindness, and nerve damage. Yet remarkably, there is limited information on whether keeping blood sugars levels tightly controlled can lower the risk of large vessel disease, namely cardiovascular disease.

Simply stated, diabetes is the body’s inability to use glucose for energy because of a lack of insulin ( type 1 ) or because the body’s tissues are resistant to insulin and not able to use it efficiently ( type 2 ). If untreated, both cases result in high blood sugar. Glycosylated hemoglobin , also called hemoglobin A1C, is a blood test that reliably indicates blood sugar control over the previous three months. A value of less than 7%, which roughly equates to an average day-to-day blood sugar level below 150 milligrams per deciliter, is recommended for people with diabetes.

A new study published in the September 21, 2004 issue of the Annals of Internal Medicine suggests that long-term blood sugar control—as measured by glycosylated hemoglobin—may indeed prevent cardiovascular diseases and events such as coronary heart disease , stroke , and peripheral arterial disease in diabetics.

About the Study

Johns Hopkins researchers searched the medical literature for published studies relating to glycosylated hemoglobin, diabetes, and cardiovascular disease. Of the 694 articles they found on these topics, they included only the 13 studies that directly measured glycosylated hemoglobin and recorded cardiovascular events such as heart attack and stroke over time.

Three of the studies looked at people with type 1 diabetes (1,688 participants) and 10 studies looked at people with type 2 diabetes (7,435 participants). The authors combined the studies’ results and used special statistical methods to summarize the relationship between blood sugar control and cardiovascular disease.

The Findings

The researchers found that the risk for cardiovascular disease increased with increasing hemoglobin A1C levels. Specifically, in people with type 2 diabetes, every 1% increase in hemoglobin A1C resulted in an 18% increase in the risk for coronary heart disease or stroke, and a 28% increase in the risk for peripheral vascular disease. Similar trends were found for people with type 1 diabetes, although the results were not statistically significant.

Although these results are interesting, there are limitations to this study. Regardless of how comprehensive the selection process was, the authors may not have identified all of the available literature on this topic. If the studies they missed did not show a clear relationship between blood sugar control and cardiovascular disease, then the actual connection would be weaker. There were also many fewer studies involving type 1 diabetes, which may explain why the results seen in this population were not statistically significant. In addition, the relationship between diabetes and cardiovascular disease is certainly not as simple at many of the studies assumed it was.

How Does This Affect You?

This study suggests that monitoring blood sugar levels often—and subsequently adjusting diet, exercise, and medications to achieve near normal blood sugar levels—may help prevent cardiovascular disease. These results make sense and are consistent with other studies showing similar benefits for the prevention of kidney, eye, and nerve complications of diabetes.

Maintaining such tight control over blood sugar levels is not easy, and there is always the increased risk of a hypoglycemic reaction in those taking medication including insulin. Still, keeping blood sugar—as measured by hemoglobin A1C—as close to normal as possible appears to be worth the effort in the long run.