Are High Sugar Levels Associated with New Cardiovascular Events in Postmenopausal Women Who Have Already Had a Heart Attack?

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The summary below is from the full report titled "Impaired Fasting Glucose and Cardiovascular Outcomes in Postmenopausal Women with Coronary Artery Disease." It is in the 17 May 2005 issue of Annals of Internal Medicine (volume 142, pages 813-820). The authors are A.M. Kanaya, D. Herrington, E. Vittinghoff, F. Lin, V. Bittner, J.A. Cauley, S. Hulley, and E. Barrett-Connor.

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

The pancreas makes a substance called insulin that helps the body turn food into stored energy. In type 2 diabetes (adult-onset diabetes), the body still makes insulin but cannot use it normally. The result is high blood sugar (glucose) levels. Over time, high blood sugar levels can lead to many complications, including heart disease and stroke (cardiovascular disease). Some people have slightly high blood sugar levels for years before reaching diabetes levels, a condition called "impaired fasting glucose." In 1997, blood sugar levels between 110 mg/dL and 125 mg/dL were defined as impaired fasting glucose. In 2003, the definition was changed to blood sugar levels between 100 mg/dL and 125 mg/dL because studies showed that even mildly high blood sugar levels were related to health problems. People who do not have cardiovascular disease are at higher risk for developing it if they have impaired fasting glucose than if they have normal blood sugar levels. Whether impaired fasting glucose increases the risk for new cardiovascular events in people who already have cardiovascular disease is not known.

Why did the researchers do this particular study?

To find out whether people with cardiovascular disease are at higher risk for having another cardiovascular event if they have impaired fasting glucose than if they have normal blood sugar levels.

Who was studied?

2768 women who were postmenopausal, had had a previous heart attack, and were participating in a study of hormone replacement therapy.

How was the study done?

The women had blood tests to measure blood sugar levels at the beginning of the study. The researchers classified women as having impaired fasting glucose by the 1997 definition, impaired fasting glucose by the 2003 definition, or normal blood sugar levels. They followed the women for almost 7 years to see who developed 1 or more of the following events: heart attack with or without death, stroke, or hospitalization for congestive heart failure. They compared the frequency of these events in women with different blood sugar levels.

What did the researchers find?

Of the 2768 women, 218 met the 1997 definition and 698 met the 2003 definition for impaired fasting glucose. The women who met the 1997 definition for impaired fasting glucose had a higher risk for cardiovascular events, but those who met the 2003 definition for impaired fasting glucose did not. This suggests that blood sugar levels were associated with cardiovascular disease only when they were 110 mg/dL or higher.

What were the limitations of the study?

The study included only postmenopausal women. The results might not apply to men or to women who have not reached menopause. This study cannot rule out a link between blood sugar levels and cardiovascular disease over periods longer than 7 years.

What are the implications of the study?

In postmenopausal women who have already had a heart attack, impaired fasting blood sugar levels between 100 mg/dL and 125 mg/dL are not associated with new cardiovascular events within the next 7 years.