Fasting Glucose Linked to Cardiovascular Risk

CAULFIELD, Australia, June 21 -- The risk of cardiovascular mortality increases at the earliest sign of impaired glucose metabolism, researchers reported here.

After adjusting for other risk factors impaired fasting glucose was associated with a 2.5-fold increase in the risk of a fatal cardiac event within five years (hazard ratio 2.5, 95% CI 1.2-5.1), said Elizabeth L.M. Barr, M.P.H., of the International Diabetes Institute, and colleagues.

Moreover diabetes or conditions considered to be pre-diabetic--impaired glucose tolerance and impaired fasting glucose-accounted for 65% of all heart disease deaths in the study of 10,429 patients (mean age 51) in the Australian Diabetes, Obesity, and Lifestyle study (AudDiab), which was published online by Circulation, Journal of the American Heart Association.

"This confirms the clinical importance of pre-diabetic conditions and suggests the need to target glucose abnormalities with lifestyle interventions-diet and exercise-to prevent these from progressing to frank diabetes," Barr said.

After adjusting for other risk factors for heart disease mortality such as age, sex, history of heart disease, smoking, blood pressure, total cholesterol to HDL ratio, and waist circumference, the increased risk associated with impaired glucose tolerance was about the same as the risk associated with known diabetes.

The five-year risk of cardiac mortality was 2.6 fold higher among people who had diabetes versus a 2.5 fold increase in risk for those with impaired glucose tolerance, Barr said. That risk, she added, was higher than the 80% increase in risk of dying form heart disease for people who were newly diagnosed with diabetes.

Impaired glucose tolerance, by contrast, was associated with a 20% increase in risk of cardiac mortality, which was significant but was only predictive of all-cause mortality.

Compared with patients who metabolized glucose normally, those with impaired glucose tolerance had a 50% increase in risk of dying within five years and people with impaired fasting glucose had a 60% increase in five-year mortality risk.

By contrast, impaired fasting glucose and diabetes were both independent predictors of cardiac mortality.

Among the findings:

• There were 298 deaths during a median 5.2 years of follow-up-an all-cause mortality rate of 5.5 per 1,000 person-years.
• Thirty-four percent of those deaths were due to heart disease.
• About 12% of the people who had diabetes at baseline died during follow-up.
• Just over 6% of participants with newly diagnosed diabetes died during follow-up versus 5.2% of participants with impaired glucose tolerance and 3.9% of those who had impaired fasting glucose.
• The five-year death rate for those who had normal glucose metabolism at baseline was 1.7%.

Study participants ages 25 or older were enrolled in 1999 and 2000 and were followed for a median of 5.2 years. At baseline all underwent oral glucose tolerance test as well as fasting plasma glucose, two-hour plasma glucose, fasting serum total cholesterol, triglycerides, and HDL measurements.

Participants were classified as known diabetics if they reported receiving a diagnosis of diabetes from a physician and were taking drugs to lower blood sugar or had blood tests that confirmed diabetes. Persons who had not previously been diagnosed with diabetes but had blood tests that indicated diabetes were classified as newly diagnosed diabetes.

Impaired fasting glucose was defined as a glucose concentration of 6.1 mmol/L or higher but less than 7.0 mmol/L and a two hour plasma glucose of less than 7.8 mmol/L. Impaired glucose tolerance was defined as a two-hour plasma glucose of at least 7.8 mmol/L but less than 11.1 mmol/l and a fasting plasma glucose of less than 7.0 mmol/L.

The authors pointed out that one limitation of the study was inadequate statistical power because of the short follow-up.