Higher Glucose Levels Increase Risk for Heart Disease

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Relation between blood glucose and coronary mortality over 33 years in the Whitehall Study, by E.J. Brunner and colleagues. Diabetes Care 29:26–31, 2006

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

People with impaired glucose tolerance have blood glucose levels that are higher than normal but not high enough to say they have diabetes. This condition is diagnosed using the oral glucose tolerance test. After not eating for 8 to 12 hours, a person's blood glucose is measured before and 2 hours after drinking a solution that contains 75 grams of glucose.

In normal glucose tolerance, blood glucose rises no higher than 140 mg/dL 2 hours after the drink.

In impaired glucose tolerance, the 2-hour blood glucose is between 140 and 199 mg/dL.

If the 2-hour blood glucose rises to 200 mg/dL or above, a person is considered to have diabetes.

When a person has higher-than-normal blood glucose levels, he or she may be more likely to develop disease of the heart and the blood vessels, but doctors are not sure what exactly the relationship is between blood glucose level and risk for heart disease.

Why did the researchers do this particular study?

Studies have shown that people with very high blood glucose levels are more likely to die from heart disease. However, researchers are not sure what level blood glucose must reach for a person to be at high risk for heart disease. Researchers did this study to find more information on the connection between blood glucose levels, glucose tolerance, and different causes of death.

Who was studied?

A total 17,869 men from London who were between 40 and 64 years old. The men were examined between September 1967 and January 1970.

How was the study done?

Between 1967 and 1970, the patients were given an oral glucose tolerance test: the men fasted overnight, then they drank a solution that contained 50 grams of glucose (most of these tests now usually use 75 grams of glucose), and 2 hours later the researchers measured their blood glucose levels to see how well the men's bodies processed the glucose. In this study, 95% of the men had glucose levels below 96 mg/dL 2 hours after drinking the solution. Therefore, this level was considered normal glucose tolerance, 96 to 199 mg/dL was considered impaired glucose tolerance, and 200 mg/dL and above was considered diabetes.

The researchers then followed up with the men over a 33-year period to check things like blood pressure and cholesterol and to record the cause of death.

What did the researchers find?

The researchers found that death from heart disease, breathing problems, and all causes was higher in participants who had higher-than-normal glucose levels. The risk for dying of problems associated with heart disease seemed to begin to increase among people who had a blood glucose level of at least 83 mg/dL 2 hours after drinking the glucose solution. The higher the glucose level above 83 mg/dL, the greater the risk. People who had a glucose level below 83 did not seem to be at risk.

What were the limitations of the study?

The limitations to the study include that the findings are based on one certain procedure for testing blood glucose, the oral glucose tolerance test with a solution containing 50 grams of glucose; a slightly different test and dose of glucose could produce a different relationship. Also, triglycerides and HDL cholesterol were not measured, and these factors could have affected the results. Finally, the people who took part in the study were all European men who were middle-aged when the study began in the late 1960s. It is possible that the study findings would not apply to a more diverse population or would be different in populations today.

What are the implications of the study?

An increase in blood glucose levels is related to an increased risk of having heart problems. Doctors should closely monitor these levels, even in patients who are considered to have normal glucose tolerance.

FOR MORE INFORMATION

Make the Link! Diabetes, Heart Disease, and Stroke

Fight Against Diabetes and Heart Disease Link Intensifies

ADA Clinical Practice Recommendations: Standards of Medical Care in Diabetes

Diabetes: A Guide to Living Well