Hypothyroidism is Not Associated with Increased Carotid Atherosclerosis when Cardiovascular Risk Factors Are Accounted for in Hyperlipidemic Patients

Overt hypothyroidism is associated with an increased prevalence of cardiovascular heart disease (CHD). The role of subclinical hypothyroidism as risk factor for cardiovascular diseases is supported by recent meta-analysis. However it still remains to be established whether hypothyroidism favors atherosclerosis independently of its effects on cardiovascular risk factors, such as hypercholesterolemia or hypertension. To assess whether hypothyroidism might be a risk factor per se, we analyzed carotid lesions assessed by US examination in two large populations with similar risk factors and displaying hypo- or euthyroidism. We selected, among a population of patients referred for assessment of hyperlipidemia, 794 hypothyroid patients (TSH>4mU/L), and 1588 euthyroid patients matched for the main cardiovascular risk factors (age, gender, lipid levels, hypertension, diabetes, smoking habits and obesity). All the patients had evaluation of their arterial carotid plaques, and about half of them had measurement of carotid intima-media thickness (IMT). Our hypothyroid population included 90% of patients with normal FT4 levels (subclinical hypothyroidism). We found that neither prevalence nor severity of carotid plaques nor carotid IMT were significantly different between hypothyroid patients and controls. To assess whether thyroid hormones may predict carotid atherosclerosis, we performed multivariate regression analyses, and we showed that, in both populations of hypothyroid and euthyroid patients, neither the TSH values nor the FT4 concentrations were independent risk factors for carotid atherosclerosis. In conclusion, we showed that, among a population of hyperlipidemic patients, hypothyroidism is not associated with an increased risk for carotid atherosclerosis when cardiovascular risk factors are accounted for.