Effect of Thyroid Hormone Replacement on Methionine-Stimulated Homocysteine Levels in Patients with Subclinical Hypothyroidism: A Randomized, Double-Blind, Placebo-Controlled Study

Abstract

Objective To determine whether treatment of subclinical hypothyroidism with levothyroxine would improve homocysteine metabolism. Methods Twenty-four patients with subclinical hypothyroidism who had thyrotropin (thyroid-stimulating hormone or TSH) levels between 5 and 10 μIU/mL and normal free thyroxine concentrations were recruited from a primary care clinic and were randomized to receive levothyroxine (N = 12) or placebo (N = 12) for a period of 6 months in a double-blind, placebo-controlled study. Homocysteine was measured during fasting and after methionine challenge at the beginning and the end of the study in all patients treated with levothyroxine or placebo. Results The 12 patients treated with levothyroxine had normal TSH levels at the end of the study, with a median value of 1.8 μIU/mL. The 12 patients receiving placebo had a median TSH of 6.0 μIU/mL after the 6-month study period. The ratio of fasting homocysteine at 6 months in comparison with baseline was 1.16 (95% confidence interval, 0.90 to 1.63) for the levothyroxine-treated group and 1.00 (0.88 to 1.29) for the placebo group (P = 0.95). The ratio of post-methionine homocysteine at 6 months in comparison with baseline was 1.00 (95% confidence interval, 0.92 to 1.35) for the levothyroxine-treated group and 0.89 (0.68 to 1.05) for the placebo group (P = 0.081). Conclusion In this study, levothyroxine treatment of patients with subclinical hypothyroidism did not alter homocysteine levels in the fasting or post-methionine states. (Endocr Pract. 2006;12:529-534)