Across 3 studies, 2 reported small beneficial effects of selenium on increasing serum free thyroxine (FT4) levels in clinical populations with thyroid disorders, while 1 found no significant effect in hemodialysis patients. The predominant effect size was small, and effects were typically observed at a dose of 200 μg per day over approximately 12 weeks. Evidence primarily comes from patients with Hashimoto thyroiditis or Graves-Basedow disease.
Caveats: Evidence base is small (only 3 studies) — conclusions should be considered preliminary. The neutral study was conducted in hemodialysis patients with nonthyroidal illness syndrome, which may differ from autoimmune thyroid populations where benefits were observed.
Significant effects on declining the TSH titers were found after 6 months (SMD = -0.18, 95%CI = -0.35 to -0.01; P = .03).
selenium supplementation was associated with significant improvements in TSH, FT4, FT3, TPOAb, TgAb, and TRAb levels
Although there were no significant differences in ... FT4 (p = 0.76) ... between the groups at the end of the trial.