More Evidence Shows a Link Between Diabetes and Heart Disease

---

Glycemic control, atherosclerosis, and risk factors for cardiovascular disease in individuals with diabetes: the Atherosclerosis Risk in Communities Study, by E. Selvin and colleagues. Diabetes Care 28:1965–1973, 2005.

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

It is already known that diabetes and high blood glucose lead to microvascular complications, or problems with the small blood vessels in the body. Diabetes decreases blood flow, and the small blood vessels are the first places affected by decreased blood flow.

But how diabetes and high blood glucose affect macrovascular health, or the health of the body's large blood vessels, is less clear.

Why did the researchers do this particular study?

The researchers of this study wanted to look at how chronically high blood glucose levels are related to the health of the large blood vessels.

Who was studied?

The researchers examined 2,060 people who had diagnosed and undiagnosed diabetes and took part in the Atherosclerosis Risk in Communities Study.

How was the study done?

On two separate occasions between 1990 and 1992, the researchers measured A1C (a measure of long-term blood glucose), lipids (or fats in the blood), weight and height, and the blood pressure of the patients. They also determined whether the patients were on any medication, smoked, drank alcohol, were on hormone therapy, and had heart-and-blood-vessel disease. They also measured the thickness of the patients' carotid arteries, the two large blood vessels in the neck. Thickening of the walls of the carotid arteries has been shown to be a sign of heart-and-blood-vessel disease and can show whether a patient has atherosclerosis. Atherosclerosis occurs when cholesterol and fat build up on artery walls, which can lead to a premature heart attack and stroke.

What did the researchers find?

Overall, A1C levels were higher in black patients than in white patients. A number of risks that lead to problems with the arteries -- high LDL cholesterol (the bad cholesterol), low HDL cholesterol (the good cholesterol), high triglycerides (another type of fat the builds up in the blood) -- were all linked to high A1C levels. The study also showed that the higher a person's A1C level, the more likely they are to have a thickening of the carotid arteries and to therefore be at a higher risk of having a heart attack or stroke.

What were the limitations of the study?

The length of this study (2 years) makes it difficult to draw long-term conclusions about the link between A1C and heart-and-blood-vessel disease. During the 2-year period, high A1C levels were not linked with prevalent heart-and-blood-vessel disease, but this could have changed over time.

During the time of the examinations, the criteria for diagnosing diabetes were different than they are now. Therefore, a number of people who were considered to have diabetes in this study would not have been considered to have diabetes during the time of the examinations.

Ninety percent of the black patients in this study were from a single study center in Jackson, Mississippi. People from other areas may lead much different lifestyles and therefore may have higher or lower A1C values.

Fasting insulin levels in this study were checked only once during the 2 years. It is possible that in some cases, high fasting insulin levels could have been temporary, although other measurements taken before 1990 seem to rule out this possibility.

What are the implications of the study?

High blood glucose levels are linked to many factors that lead to heart-and-blood-vessel disease, such as high triglyceride and cholesterol levels. In particular, high blood glucose levels are linked to a thickening of the carotid arteries and therefore may play a role in the development of atherosclerosis in people with diabetes.

For people with diabetes, it is especially important to lead a heart-healthy lifestyle. For more information on the link between diabetes and heart disease, visit Make the Link!, a joint initiative of the American Diabetes Association and the American College of Cardiology.

For more information

A1C Test

Identifying individuals at high risk for diabetes: the Atherosclerosis Risk in Communities Study, by M. Inês Schmidt and colleagues. Diabetes Care 28:2013–2018, 2005.

Fast Facts Series: Keeping Your Heart Healthy Despite Diabetes (Alexandria, Va., ADA, 2002)