Selenium Supplementation and Thyroid

GRAND FORKS, N.D.—–A recent study found selenium supplementation produced no clinically significant changes in thyroid hormone concentrations; however, a small but statistically significant increase in triiodothyronine (T3) concentrations was noted in men, with no corresponding decreases in thyrotropin (TSH) (Am J Clin Nutr. 2009;89(6):1808-14).

Twenty-eight healthy adults took 200 µg of selenomethionine/d for 28 months. The thyroid hormones thyroxine (T4) and TSH were measured in plasma for four months before supplementation and quarterly during supplementation. The assay methods were changed midstudy; the results of the 2 methods were not comparable. Therefore, one analysis was conducted based on the results of the first method, and a second analysis was based on all of the data, adjusted for the change. Serial data collection permitted a test for trends rather than simply a difference between initial and final values.

By nine months, mean plasma selenium concentrations had increased from 1.78 ± 0.07 µmol/L at baseline to 2.85 ± 0.11 µmol/L for men and from 1.64 ± 0.04 to 3.32 ± 0.1.2 µmol/L for women. T3 concentrations in men increased 5 percent per year (P=0.01). T4 and TSH concentrations were unchanged.