Effects of Zinc and Selenium Supplementation on Thyroid Function in Overweight and Obese Hypothyroid Female Patients: A Randomized Double-Blind Controlled Trial

Objective: Zinc (Zn) and selenium (Se) are essential trace elements involved in thyroid hormone metabolism. This study was conducted to investigate the effects of Zn and Se supplementation on thyroid function of overweight or obese female hypothyroid patients in a double-blind, randomized controlled trial.Methods: Sixty-eight female hypothyroid patients were randomly allocated to one of the 4 supplementation groups receiving Zn + Se (ZS; 30mg Zn as zinc-gluconate and 200g Se as high-selenium yeast), Zn + placebo (ZP), Se + placebo (SP), or placebo + placebo (PP) for 12 weeks. Serum Zn, Se, free and total triiodothyronine (FT3 and FT4), free and total thyroxine (FT4 and TT4), thyroid-stimulating hormone (TSH), and anthropometric parameters were measured. Dietary intake was recorded using 24-hour food recall. Physical activity questionnaire was completed.Results: No significant alterations were found in serum Zn or Se concentrations. Mean serum FT3 increased significantly in the ZS and ZP groups (p < 0.05) but this effect was significant in the ZP group compared to those in SP or PP groups (p < 0.05). Mean serum FT4 increased and TSH decreased significantly (p < 0.05) in the ZS group. TT3 and TT4 decreased significantly in the SP group (p < 0.05). Mean FT3:FT4 ratio was augmented significantly in the ZP group (p < 0.05). No significant treatment effects were found for TT3, FT4, TT4, or TSH between groups.Conclusion: This study showed some evidence of an effect of Zn alone or in combination with Se on thyroid function of overweight or obese female hypothyroid patients.