Clinical evidence of impairment in glucose metabolism as small as just an abnormal fasting glucose level increases the risk for death from heart disease, according to an article in the June 19 issue of Circulation.

In the Australian Diabetes, Obesity and Lifestyle Study (AusDiab), participants with impaired fasting glucose, a condition considered pre-diabetes, "after five years were more than twice as likely to die of cardiovascular disease," said Elizabeth L.M. Barr, MPH, lead author of the study at the International Diabetes Institute in Melbourne, Australia.

"Moreover, diabetes and pre-diabetes (impaired glucose tolerance and impaired
fasting glucose) accounted for 65 percent of all heart disease deaths in the
study of 10,429 Australians."

Study participants age 25 years or older were enrolled in 1999 and 2000 and followed for a median of 5.2 years. At baseline, all participants underwent an oral glucose tolerance test, fasting serum total cholesterol, triglycerides and high-density-lipoprotein cholesterol measurements.

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

In addition to participants whose physician had diagnosed diabetes, participants whose study bloodwork showed diabetes were considered diabetics for the purpose of analysis. After adjusting for other risk factors for heart disease mortality such as age, sex, history of heart disease, smoking, blood pressure, total cholesterol to high-density lipoprotein cholesterol ratio, and waist circumference, the increased risk associated with impaired fasting glucose was about the same as the risk associated with known diabetes.

During follow-up (median, 5.2 years), 298 deaths occurred, for an all-cause mortality rate of 5.5 per 1,000 person-years. Of those deaths, 88 were due to heart disease.

Almost 12 percent of people with known diabetes at baseline died during follow-up compared with 6.2 percent of those newly diagnosed with diabetes, 5.2 percent of participants with impaired glucose tolerance, and 3.9 percent of those with impaired fasting glucose. The five-year death rate for those who had normal glucose metabolism at baseline was 1.7 percent.

"The five-year risk of cardiac mortality was 2.6 times higher among people who
had diabetes and was 2.5 times higher in those with impaired fasting glucose,"
Barr said.

Impaired glucose tolerance, by contrast, was associated with a 20 percent increase in risk of cardiac mortality, which was not statistically significant, unlike impaired fasting glucose and known diabetes, which were both independent predictors of heart disease death. Impaired glucose tolerance was, however, predictive of all-cause mortality.

Compared with people who metabolized glucose normally, the five-year total mortality risk was 50 percent higher for people with impaired glucose tolerance and 60 percent higher for people with impaired fasting glucose.