Plasma leptin is independently associated with the intima-media thickness of the common carotid artery

OBJECTIVE: To investigate whether intima-media thickness (IMT) of the common carotid artery (CCA), an early marker of asymptomatic atherosclerosis, is significantly and independently associated with plasma concentrations of leptin, an adipose tissue hormone that has recently been proposed as a cardiovascular risk factor in obese patients. DESIGN: Cross-sectional sample of normal-weight and obese men and women. SUBJECTS: One-hundred and twenty healthy subjects (52 men and 68 women), aged 18-45 y and with a wide range of BMI, were recruited for the study. MEASUREMENTS: Fasting plasma leptin concentrations and the IMT of the CCA were measured in all subjects. Leptin concentrations were measured by radioimmunoassay and the IMT of the CCA was quantified by high resolution B-mode ultrasound imaging. Central fat (measured by waist circumference), smoking habits, blood pressure, insulin sensitivity (measured by the insulin tolerance test), and fasting plasma glucose, insulin and lipid pattern (cholesterol, HDL-cholesterol, triglycerides, LDL-cholesterol) were also measured. RESULTS: IMT of the CCA was positively correlated with log leptin concentrations (P < 0.005 in men and P < 0.001 in women), body mass index (P < 0.001 in men and women), waist circumference (P < 0.001 in men and women), age (P < 0.001 in men and P < 0.05 in women), and negatively associated with insulin sensitivity in both sexes (P < 0.05). IMT was also directly correlated with cholesterol (P < 0.05), LDL-cholesterol (P < 0.01) and systolic blood pressure in men (P < 0.05), and with diastolic blood pressure levels in women (P < 0.05). When a multiple linear regression model was used without body mass index (BMI), the correlation between leptin and IMT was maintained in both men (P < 0.01) and women (P < 0.005), independent of age, insulin sensitivity, smoking habits, systolic blood pressure, fasting glucose, triglycerides, cholesterol, LDL-cholesterol and HDL-cholesterol. By contrast, BMI-adjusted leptin concentrations were not significantly associated with IMT (Pc (partial correlation): 0.41 in men and 0.15 in women). Moreover, when BMI was entered into a multiple linear regression model without leptin, the correlation between BMI and IMT was maintained in both men (P < 0.005) and women (P < 0.01), independent of the same parameters. CONCLUSION: Plasma leptin concentrations are independently associated with the IMT of the CCA, suggesting that the increase of adipose tissue mass (or leptin per se) may have an unfavourable influence on the development of atherosclerosis. However, the association between IMT and leptin seems to be dependent and/or confounded by the relationship between IMT and obesity.