Impaired Glucose Tolerance, but not Impaired Fasting Glucose, Is Associated With Increased Levels of Coronary Heart Disease Risk Factors

Impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) identify individuals at high risk for progression to diabetes. Whether IFG and IGT have comparable coronary heart disease (CHD) risk factor profiles, independent of their progression to diabetes, is unclear. We determined CHD risk factor levels in 937 nondiabetic individuals at baseline and biannually over a mean follow-up period of 9.5 years. Subjects had no known CHD at baseline and had ≥2 (mean 4.2) oral glucose tolerance tests during follow-up. We classified glucose tolerance categories using American Diabetes Association diagnostic criteria or modified criteria that redefined IFG as 100–126 mg/dl, creating a similar baseline prevalence of IFG and IGT. Subjects who developed diabetes during follow-up were excluded from our analysis. Baseline CHD risk factors were similar in subjects with normal glucose tolerance (NGT) and IFG, but significantly more atherogenic in those with IGT or IFG + IGT. These findings were unchanged when the modified criteria were used, suggesting that IGT is phenotypically different from IFG and is associated with increased levels of CHD risk factors. Subjects with isolated IFG had similar levels of CHD risk factors as NGT subjects, even when IFG was redefined with a lower threshold. Although CHD risk factors were increased in the IGT group, the incidence of CHD events was not significantly different among groups, perhaps owing to the limited number of events. The differences in CHD risk factors among prediabetic groups may have clinical implications for screening strategies and CHD risk stratification of individuals with IFG and IGT.