SUMMARIES FOR PATIENTS

Insulin Resistance Is Associated with Abnormalities of Coronary Arteries in People without Other Cardiac Risk Factors

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The summary below is from the full report titled "Coronary Vasomotor Abnormalities in Insulin-Resistant Individuals." It is in the 4 May 2004 issue of Annals of Internal Medicine (volume 140, pages 700-708). The authors are M.J. Quiñones, M. Hernandez-Pampaloni, H. Schelbert, I. Bulnes-Enriquez, X. Jimenez, G. Hernandez, R. De La Rosa, Y. Chon, H. Yang, S.B. Nicholas, T. Modilevsky, K. Yu, K. Van Herle, L.W. Castellani, R. Elashoff, and W.A. Hsueh.

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

Insulin is a substance made by the pancreas to help the body store energy from food. People with type 2 diabetes mellitus make plenty of insulin, but their bodies cannot use it normally, resulting in high blood sugar levels. Some people do not have type 2 diabetes but have "insulin resistance." People with insulin resistance do not have the high blood sugar levels that occur in people with type 2 diabetes, but their bodies must produce large amounts of insulin to keep sugar levels normal. Insulin resistance can progress to type 2 diabetes. People with type 2 diabetes have a high risk for heart disease. Some studies suggest that insulin resistance is also associated with heart disease but could not determine whether the higher rates of heart diseases in people with insulin resistance were due to the insulin resistance or to other risk factors for heart disease, such as high blood pressure, smoking, or abnormal cholesterol levels.

Why did the researchers do this particular study?

To see whether people with insulin resistance and no other risk factors for cardiovascular disease are more likely to have abnormalities of the heart's blood vessels than similar people without insulin resistance.

Who was studied?

50 young adults with no risk factors for heart disease except insulin resistance and 22 similarly aged young adults without insulin resistance or other risk factors for heart disease. All study participants were Mexican American.

How was the study done?

First, the researchers determined whether people were insulin-resistant by using a special blood test in which sugar and insulin are delivered through a small tube inserted into an arm vein. Next, they studied the blood flow to the heart by using positron emission tomography, which evaluated the function of the lining and muscular wall of the heart's blood vessels during various situations. In addition, they repeated the tests in 26 of the insulin-resistant people after giving them a medication to treat insulin resistance.

What did the researchers find?

The tests that examined the function of the muscle in the wall of the heart blood vessels showed no differences between insulin-resistant and healthy people. However, the test result of the blood vessel lining was abnormal in insulin-resistant patients. This defect in the vessel lining is important because it is the first step for developing heart disease. These abnormalities went away after the 22 patients received the medication to treat insulin resistance.

What were the limitations of the study?

This study involved a small number of people from one ethnic group. In addition, it examined blood vessel function, not actual heart disease events. Additional studies are necessary to determine whether treating people with insulin resistance before it progresses to diabetes will decrease their chances of developing heart disease.

What are the implications of the study?

Even before diabetes develops, people with insulin resistance and no other risk factors for heart disease have abnormalities of the heart's blood vessels.