Endothelial dysfunction and the risk of atherosclerosis in overt and subclinical hypothyroidism

Hypothyroidism is associated with increased risk of atherosclerosis. We assessed carotid intima-media thickness (CIMT), as a marker of atherosclerosis, and endothelial function in patients with hypothyroidism. We included 70 female patients with hypothyroidism in the study, 40 patients with overt and 30 patients with subclinical hypothyroidism. Forty, age- and sex-matched, subjects with normal thyroid functions were also included as a control group. CIMT was measured using high-resolution color-coded Doppler ultrasonography. Endothelial function was assessed by measuring the percent of change in blood flow following heat-mediated vasodilation using laser Doppler flowmetry. CIMT was significantly higher in patients with overt and subclinical hypothyroidism as compared with the control group (0.7 +/- 0.2 and 0.6 +/- 0.2 mm respectively vs 0.45 +/- 0.07mm, P< 0.001 for both). The percent of change in blood flow following heat-mediated vasodilation was significantly impaired in patients with overt and subclinical hypothyroidism as compared with the control group (328 +/- 17 and 545 +/- 406% respectively vs 898 +/- 195%, P< 0.001 for both). The impairment was more significant in overt as compared with subclinical hypothyroidism (P=0.014). CIMT negatively correlated with percent of change in blood flow following heat-mediated vasodilation in patients with overt and subclinical hypothyroidism (P< 0.001 for both). We concluded that CIMT is significantly higher in patients with overt and subclinical hypothyroidism compared with normal control subjects. Impairment of endothelial function is a contributing factor to the increased risk of atherosclerosis in both groups of patients.