The Relationship between Blood Sugar Control and Cardiovascular Disease in Patients with Diabetes

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The summary below is from the full report titled "Meta-Analysis: Glycosylated Hemoglobin and Cardiovascular Disease in Diabetes Mellitus." It is in the 21 September 2004 issue of Annals of Internal Medicine (volume 141, pages 421-431). The authors are E. Selvin, S. Marinopoulos, G. Berkenblit, T. Rami, F.L. Brancati, N.R. Powe, and S. Hill Golden.

What is the problem and what is known about it so far?

Diabetes interferes with the body's ability to store energy from food. The pancreas makes a substance called insulin that helps the body to turn food into stored energy. Type 1 diabetes (juvenile diabetes) occurs when the pancreas stops making insulin. In type 2 diabetes (adult-onset diabetes), the body still makes insulin but cannot use it normally. In both cases, the result is high blood sugar levels. Over time, high blood sugar levels can lead to many complications, including blindness, kidney failure, nerve damage, and cardiovascular disease (heart disease and stroke). Fortunately, good care with diet, exercise, and medications to control blood sugar levels clearly prevents or delays the development of diabetes-related blindness, kidney failure, and nerve damage. The relationship between blood sugar control and cardiovascular disease is less clear. Glycosylated hemoglobin is a blood test that measures blood sugar control over the previous 3 months.

Why did the authors do this meta-analysis?

To summarize evidence from previous studies to determine the strength of the relationship between glycosylated hemoglobin levels and cardiovascular disease in patients with diabetes.

How did the authors do this meta-analysis?

The researchers searched the computerized database of the National Library of Medicine for studies related to glycosylated hemoglobin, diabetes, and cardiovascular disease. They included only studies that first measured glycosylated hemoglobin levels and then followed patients to see whether they developed cardiovascular disease. The authors used special statistical techniques to combine the information from the studies in order to more precisely estimate the relationship than would be possible in any single study by itself.

What did the authors find?

Of studies that met their requirements, the authors found 3 studies involving 1688 patients with type 1 diabetes and 10 studies involving 7435 patients with type 2 diabetes. When they combined the data from these studies, the researchers found that the risk for cardiovascular disease increased with increasing glycosylated hemoglobin levels. Higher levels means worse blood sugar control. The relationship was present and similar for both type 1 and type 2 diabetes.

What are the implications of the meta-analysis?

Poor control of blood sugar levels in people with type 1 or type 2 diabetes is associated with the development of cardiovascular disease. These findings suggest, but cannot prove, that improved blood sugar levels will decrease the chances that a person with diabetes will develop cardiovascular disease.