Insulin Resistance Independently Predicts the Progression of Coronary Artery Calcification

Change in coronary artery calcification is a surrogate marker of subclinical coronary artery disease (CAD). In the only large prospective study, CAD risk factors predicted progression of coronary artery calcium (CAC).

For the study theymeasured CAC at enrollment and after 24 months in a community-based sample of 869 healthy adults aged 60 to 72 years who were free of clinical CAD. They assessed predictors of the progression of CAC using univariate and multivariate models after square root transformation of the Agatston scores. Predictors tested included age, sex, race/ethnicity, smoking status, body mass index, family history of CAD, C-reactive protein and several measures of diabetes, insulin levels, blood pressure, and lipids.

The results showed that the mean age of the cohort was 66 years, and 62% were male. The median CAC at entry was 38.6 Agatston units and increased to 53.3 Agatston units over 24 months (P < .01). The CAC progression was associated with white race, diabetes, dyslipidemia, hypertension, lower diastolic blood pressure, and higher pulse pressure. After controlling for these variables, higher fasting insulin levels independently predicted CAC progression.

Diabetes was one of the strongest predictor of CAC progression in this study because each diabetes-related measure was found to be a statistically significant predictor in the univariate model. Furthermore, the diagnosis of diabetes based on all available data was one of the best overall predictors of CAC progression in the multivariate analysis.

Fasting insulin, an indicator of insulin resistance, was an independent predictor of CAC progression as well, even after adjusting for the diagnosis of diabetes. This result is not surprising because insulin resistance is the underlying cause of Type 2 diabetes and is present in many individuals without frank diabetes. Adding to the plausibility of this finding, other investigators report a positive association between fasting insulin and severity of CAD in patients undergoing elective coronary angiography.

This study confirms that the traditional cardiac risk factors of diabetes, dyslipidemia, and hypertension independently predict CAC progression in a community-based sample of older adults free of clinical CAD. These results are consistent with the results of the large prospective Multi-Ethnic Study of Atherosclerosis, small prospective studies of diabetic patients, and the findings of retrospective studies in other selected populations. They also found that insulin resistance independently predicts CAC progression, which has not been reported previously.

From the results it was concluded that insulin resistance, in addition to the traditional cardiac risk factors, independently predicts progression of CAC in a community-based population without clinical CAD.