Flow-mediated, endothelium-dependent vasodilation is impaired in subjects with hypothyroidism, borderline hypothyroidism, and high-normal serum thyrotropin (TSH) values.

Patients with hypothyroidism are considered to have an increased risk of developing atherosclerosis; because endothelial dysfunction is an early sign of atherosclerosis, we investigated whether endothelial dysfunction is present in patients with hypothyroidism. Thirty-five subjects with various TSH levels were investigated by high-resolution ultrasound imaging of the brachial artery to assess endothelial and smooth muscle responses. Flow-mediated, endothelium-dependent vasodilatation was significantly higher in subjects with TSH 0.4-2 microIU/mL (11.8 +/- 2.7%), compared with subjects with TSH 2.01-4 microIU/mL (6.8 +/- 2.9%), 4.01-10 microIU/mL (5.2 +/- 6.3%) and >10 microIU/mL (4.0 +/- 4.4%); TSH levels correlated inversely to endothelium-dependent dilatation. Thus, flow-mediated vasodilatation, a marker of endothelial function, is impaired not only in patients with mild hypothyroidism but also in subjects with "high-normal" serum TSH levels (ie, 2.01-4.0 microIU/mL) that may be characterized as possibly abnormal.