Cardiovascular risk factors in confirmed prediabetic individuals. Does the clock for coronary heart disease start ticking before the onset of clinical diabetes?

Although type II diabetes is associated with both microvascular and macrovascular complications, duration of diabetes and severity of glycemia are strongly associated only with the former. Since prediabetic individuals are hyperinsulinemia, and since hyperinsulinemia may be a cardiovascular risk factor, we hypothesized that prediabetic individuals might have an atherogenic pattern of risk factors even before the onset of clinical diabetes, thereby explaining the relative lack of an association of macrovascular complications with either glycemic severity or disease duration. We documented the cardiovascular risk factor status of 614 initially nondiabetic Mexican Americans who later participated in an 8-year follow-up of the San Antonio Heart Study, a population-based study of diabetes and cardiovascular disease. Individuals who were nondiabetic at the time of baseline examination, but who subsequently developed type II diabetes (ie, confirmed prediabetic subjects, n = 43), had higher levels of total and low-density lipoprotein cholesterol, triglyceride, fasting glucose and insulin, 2-hour glucose, body mass index, and blood pressure, and lower levels of high-density lipoprotein cholesterol than subjects who remained nondiabetic (n = 571). Most of these differences persisted after adjustment for obesity and/or level of glycemia, but were abolished after adjustment for fasting insulin concentration. When subjects with impaired glucose tolerance at baseline (n = 106) were eliminated, the more atherogenic pattern of cardiovascular risk factors was still evident (and statistically significant) among initially normoglycemic prediabetic subjects. These results indicate that prediabetic subjects have an atherogenic pattern of risk factors (possibly caused by obesity, hyperglycemia, and especially hyperinsulinemia), which may be present for many years and may contribute to the risk of macrovascular disease as much as the duration of clinical diabetes itself.