Old and New Definitions of Impaired Fasting Glucose Predict CHD in Women, but Not Men

Shelley Wood
January 15, 2008 — The revised, 2003 definition for impaired fasting glucose offers little in the way of benefit over the 1997 definition in terms of predicting risk of cardiovascular disease or diabetes, a new analysis suggests [1]. Writing in the January 15, 2008 issue of the Journal of the American College of Cardiology, Dr Yamini S Levitzky (National Heart, Lung, and Blood Institute's [NHLBI's] Framingham Heart Study, MA) and colleagues observe that there may be important gender differences in the predictive powers of impaired fasting glucose, suggesting that coronary heart disease (CHD) risk in women may be increased at lower glucose levels than in men.
In an interview with heartwire, senior author on the study Dr Caroline Fox (National Heart, Lung, and Blood Institute, Bethesda, MD), explained that the primary reason for undertaking the study was to see how the new definition of impaired fasting glucose compared with the old in terms of predicting diabetes and cardiovascular disease. The American Diabetes Association first proposed using a fasting plasma glucose level between 110 and 125 mg/dL as a means of identifying people as "prediabetics" in 1997; in 2003, the lower threshold was reduced to 100 mg/dL, nearly tripling the number of US adults in this prediabetic category; however, very few studies have looked at whether the 2003 definition adds anything to the risk prediction provided in the 1997 definition of impaired fasting glucose, particularly for estimating risk of developing cardiovascular disease (CVD).
Their study examined Framingham Heart Study "offspring participants" with no CVD at baseline, followed between 1983 and 2004. Among women who met the definition of impaired fasting glucose according to either the 1997 or 2004 definition, the risk of coronary heart disease over four years was significantly increased as compared with women with normal glucose levels. In men, however, neither definition was predictive of coronary heart disease. When cardiovascular disease, which included end points like claudication, transient ischemic attack, stroke, and congestive heart failure, was the outcome of interest, only impaired fasting glucose according to the 1997 definition was significantly predictive of subsequent events, and only in women.
Risk of developing diabetes was significantly increased in both men and women when either the 1997 or 2004 definition of impaired fasting glucose was used; however, the risk of developing diabetes associated with impaired fasting glucose was slightly higher when the 1997 definition was used.
Fasting glucose tests may be more beneficial in women?
"One of the interesting aspects of the results was the pretty striking difference in the predictive capacity of impaired fasting glucose for the development of both diabetes and cardiovascular disease in women as compared with men," Fox commented. "What we found is that for any given category of glucose, women did have a higher relative risk of developing diabetes or cardiovascular disease."
That said, men had a higher absolute risk of developing cardiovascular disease, Fox added.
While the findings are not "particularly surprising," Fox said, "the sex differences were stronger than we might have imagined."
Further studies are warranted to see if these sex differences persist in other large cohorts and, in particular, in other ethnic and socioeconomic groups, she added.
Source
Levitzky YS, Pencina MJ, D'Agostino RB, et al. Impact of impaired fasting glucose on CVD. The Framingham Study. J Am Coll Cardiol. 2008;51:264-270.