Flow-Mediated, Endothelium-Dependent Vasodilatation 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 highresolution ultrasound imaging of the brachial artery to assess endothelial and smooth muscle responses. Flowmediated, endothelium-dependent vasodilatation was significantly higher in subjects with TSH 0.4–2 μIU/mL (11.8 ± 2.7%), compared with subjects with TSH 2.01-4 μIU/mL (6.8 ± 2.9%), 4.01-10 μIU/mL (5.2 ± 6.3%) and >10 μIU/mL (4.0 ± 4.4%); TSH levels correlated inversely to endothelium-dependent dilatation. Thus, flowmediated 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 μIU/mL) that may be characterized as possibly abnormal.