SUMMARIES FOR PATIENTS

The Relationship Between Blood Sugar Levels and Cardiovascular Disease

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The summary below is from the full report titled "Association of Hemoglobin A_1c with Cardiovascular Disease and Mortality in Adults: The European Prospective Investigation into Cancer in Norfolk." It is in the 21 September 2004 issue of Annals of Internal Medicine (volume 141, pages 413-420). The authors are K.-T. Khaw, N. Wareham, S. Bingham, R. Luben, A. Welch, and N. Day.

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 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 makes adequate amounts of 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 a number of 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 concentration is a blood test that measures blood sugar control over the previous 3 months.

Why did the researchers do this particular study?

To determine whether glycosylated hemoglobin levels are associated with cardiovascular disease and death from any cause in adults with and without with diabetes.

Who was studied?

4662 men and 5570 women who were 45 to 79 years of age and who lived in Norfolk, United Kingdom. The people in this study were participating in a larger study of cancer risks.

How was the study done?

During 1995 to 1997, the researchers collected blood specimens to measure glycosylated hemoglobin levels and asked patients about cardiovascular risk factors, such as smoking, high blood pressure, and diabetes. The researchers then followed patients through 2003 and collected information about who developed cardiovascular disease (such as heart disease or stroke) and who died.

What did the researchers find?

During the study, 806 people developed cardiovascular disease and 521 died. The greater a person's glycosylated hemoglobin levels were at the start of the study, the more likely they were to develop cardiovascular disease or die. The level of glycosylated hemoglobin was associated with these events, even in people who did not have diabetes and who had glycosylated hemoglobin levels within the normal range.

What were the limitations of the study?

This study cannot determine whether treatment to lower glycosylated hemoglobin levels would lower a person's chance of cardiovascular disease or death.

What are the implications of the study?

Glycosylated hemoglobin levels are associated with cardiovascular disease and death, even among people who do not have diabetes.