Intimal-medial thickness of the carotid artery in nondiabetic and NIDDM patients. Relationship with insulin resistance.

OBJECTIVE: The aim of this study was 1) to compare intimal-medial thickness (IMT) of the carotid artery in nondiabetic and NIDDM patients and 2) to evaluate the association of this early marker of atherosclerosis with several cardiovascular risk factors, including plasma insulin and insulin resistance.

RESEARCH DESIGN AND METHODS: A total of 58 nondiabetic and 56 NIDDM patients, randomly selected among those attending the outpatient Diabetes Clinic or the Clinic for Internal Medicine were examined. BMI, waist-to-hip ratio (WHR), blood pressure, glycohemoglobin (HbA1c), and fasting concentrations of plasma glucose, serum lipids (total and HDL cholesterol, triglycerides), and serum insulin were measured. Insulin resistance was assessed by computing glucose disappearance rate from plasma after intravenous insulin injection (Kitt). IMT of the carotid artery was measured by ultrasonography.

RESULTS: IMT was significantly higher in diabetic patients, and the difference remained highly significant after adjusting for sex, age, BMI, WHR, presence of hypertension and dyslipidemia, and smoking status (1.39 vs. 1.24 mm, common SD 0.12, P < 0.001). Univariate regression analyses showed that IMT was negatively correlated with Kitt in either nondiabetic (r = -0.348, P < 0.01) or diabetic patients (r = -0.492, P < 0.001). However, multiple regression analyses showed that IMT was independently associated with age and WHR in nondiabetic subjects, whereas in diabetic patients, IMT was independently predicted by Kitt and hypertension. These two variables explained approximately 62% and approximately 35% of the variability of IMT in nondiabetic and diabetic patients, respectively. Plasma insulin was not independently associated with IMT in either groups.

CONCLUSIONS: These results indicate that 1) diabetes is characterized by a greater thickness of the carotid artery independently of other established risk factor of atherosclerosis, 2) early atherosclerosis is independently associated with insulin resistance in diabetic but not in nondiabetic patients, 3) central adiposity is an independent predictor of IMT in nondiabetic individuals.