Influence of short-term selenium supplementation on the natural course of Hashimoto’s thyroiditis: clinical results of a blinded placebo-controlled randomized prospective trial

Background: The real efficacy of selenium supplementation in Hashimoto’s thyroiditis (HT) is still an unresolved issue. Objectives: We studied the short-term effect of l-selenomethionine on the thyroid function in euthyroid patients with HT. Our primary outcome measures were TSH, thyroid hormones, thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TGAb) levels and thyroid echogenicity after 6 months of l-selenomethionine treatment. The secondary outcome measure was serum CXCL10 levels. Methods: In a placebo-controlled randomized prospective study, we have enrolled untreated euthyroid patients with HT. Seventy-six patients were randomly assigned to receive l-selenomethionine 166 µg/die (SE n = 38) or placebo (controls n = 38) for 6 months. TSH, free T₄ (FT₄), free T₃ (FT₃), TPOAb and CXCL10 serum levels were assayed at time 0, after 3 and 6 months. An ultrasound examination of the left and right thyroid lobe in transverse and longitudinal sections was performed. A rectangular region, the region of interest, was selected for analysis. Results: TSH, FT4, FT3, TPOAb, thyroid echogenicity and CXCL10 were not statistically different between SE and control groups at time 0, after 3 and 6 months. In the SE group, FT₄ levels were significantly decreased (P < 0.03) after 3 months, while FT₃ increased (P < 0.04) after 3 and 6 months versus baseline values. In the control group, the FT₃ decreased after 3 and 6 months (P < 0.02) compared to baseline. Conclusion: The short-term l-selenomethionine supplementation has a limited impact on the natural course in euthyroid HT. Our results tip the balance toward the ineffectiveness of short-term l-selenomethionine supplementation in HT.