NEW YORK - Among healthy middle-aged and older women, the hemoglobin A1c level -- a measure of blood sugar control -- is an independent predictor of type 2 diabetes, a study shows.

Hemoglobin A1c (HbA1c) is a marker of cumulative exposure to glucose (sugar) over the preceding 2- to 3-month period, Dr. Aruna D. Pradhan, of Brigham and Women's Hospital, Boston, and colleagues explain in the American Journal of Medicine.

Whether mild elevations of this biomarker provide prognostic information on the occurrence of type 2 diabetes and cardiovascular disease among individuals at "usual risk" for these disorders is uncertain, the investigators continue.

Pradhan and colleagues examined whether baseline HbA1c levels can predict diabetes and a first heart-related event in 26,563 participants of the Women's Health Study who at the outset were at least 45 years of age and did not have diabetes or cardiovascular disease.

A total of 1,238 cases of diabetes and 684 cardiovascular events occurred during follow-up, which lasted a median of 10 years.

They observed a graded increase in risk for both diabetes and heart-related events, such as heart attack, with increasing levels of HbA1c.

HbA1c remained a strong predictor of diabetes, but not heart-related events, in analyses adjusting for multiple factors that might influence the results.

"Although these data do not support the use of HbA1c as a single measure of diabetes risk, our results do suggest that the prognostic significance of elevated HbA1c may warrant a greater emphasis in primary prevention," Pradhan's team concludes.

SOURCE: American Journal of Medicine, August 2007.