Relationship Between Insulin and Carotid Atherosclerosis in the General Population

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Abstract
Background and Purpose Although several studies have investigated the association between insulin and coronary heart disease, the relationship between this hormone and carotid atherosclerosis is not well established. Methods As a part of a population-based survey on atherosclerosis and its risk factors, serum insulin was measured at fasting (n=888) and at 2 hours after an oral glucose load (n=811; known diabetic subjects were excluded). The study population comprised an age- and sex-stratified random sample of men and women aged 40 to 79 years. Atherosclerosis in the common and internal carotid arteries was assessed twice (in 1990 and 1995) by duplex sonography. Progression during the 5-year follow-up was defined by an increase in the atherosclerosis score of more than the doubled measurement error (>27%) or by the occurrence of new plaques. Subjects were stratified in quintiles according to baseline serum insulin at fasting or 2 hours after glucose loading. Results Logistic regression analysis revealed a significant association of carotid atherosclerosis with both low and high insulin (U-shaped relation). This finding was found before and after adjustment for several covariates (sex, age, body mass index, glucose tolerance, triglycerides, apolipoproteins A1 and B, fibrinogen, blood pressure status, behavioral variables, and socioeconomic status). This relation applied equally to fasting and postglucose insulin and was more pronounced in the prospective analysis than in the cross-sectional analysis. Conclusions We conclude that both “hypoinsulinemia” and hyperinsulinemia are independent risk indicators of carotid atherosclerosis.