Endothelial dysfunction in patients with subclinical hypothyroidism and the effects of treatment with levothyroxine

Background: Subclinical hypothyroidism (SHT) may increase the risk of cardiovascular disease. We compared endothelial function between SHT patients and euthyroid individuals, and evaluated the effects of levothyroxine therapy on endothelial function in the patients. Materials and Methods: In a quasi-experimental study, flow-mediated dilatation (FMD) and intima-media thickness (IMT) were assessed in SHT patients and healthy controls ( n = 25 in each group). Patients then received levothyroxine (50 μg/day) for 2 months, and the FMD and IMT assessments were repeated. Results: Patients and controls were similar in IMT (0.56 ± 0.09 vs. 0.58 ± 0.08 mm, P = 0.481), but FMD was lower in patients than in controls (4.95 ± 2.02 vs. 6.50 ± 2.57%, P = 0.011). A significant increase was observed in FMD (4.11 ± 2.37%, P = 0.001), but not in IMT (−0.004 ± 0.020 mm, P = 0.327), after levothyroxine therapy among the patients. Conclusions: Patients with SHT have endothelial dysfunction which responds to levothyroxine therapy. Randomized placebo-controlled trials are needed to confirm these findings.