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Selenium

What does the research say about Selenium?

4 health outcomes synthesised

Research on selenium has examined its effects across four health outcomes, primarily involving thyroid autoimmunity. The strongest evidence, supported by 5 studies, shows that selenium supplementation consistently reduces thyroid peroxidase antibody levels in patients with Hashimoto thyroiditis, with moderate to large effect sizes. However, no specific dose or form of selenium has been consistently identified across studies, limiting actionable recommendations.

Strongest evidence: The only outcome with high evidence strength is the reduction of thyroid peroxidase antibody (TPOAb) levels. Across 5 studies (4 beneficial, 1 neutral), selenium supplementation showed consistent benefits in patients with Hashimoto thyroiditis and Graves-Basedow disease, with moderate to large effect sizes observed at 3 and 6 months. No specific dose or form was consistently reported across studies.

Mixed or weaker evidence: Three outcomes have low evidence strength. For reduced thyroglobulin antibody levels, results were mixed: 2 of 4 studies showed benefit, but effects were small and time-dependent (observed at 3 months but not 6 months). Improved cognitive function was tested in 3 studies, with only 1 observational study showing a small benefit in elderly adults—no causal conclusions can be drawn. Increased serum free thyroxine levels showed small benefits in 2 of 3 studies, primarily in autoimmune thyroid populations.

Effective dose patterns: The only consistent dose identified across outcomes is for increasing free thyroxine levels, where 200 μg per day was used over approximately 12 weeks. For other outcomes, no effective dose range was consistently reported, and data on specific selenium forms (e.g., selenomethionine, sodium selenite) are lacking.

Population insights: Most beneficial effects were observed in patients with autoimmune thyroid disorders (Hashimoto thyroiditis, Graves-Basedow disease). Cognitive function research involved elderly adults (60+ years) and stroke survivors, but evidence remains preliminary. Hemodialysis patients with nonthyroidal illness syndrome showed neutral results for free thyroxine levels, suggesting benefits may be limited to autoimmune populations.

Notable caveats: The evidence base overall is small, with each outcome drawing from 3–5 studies. Several meta-analyses showed inconsistent results across timepoints or did not reach statistical significance. One TPOAb study included a combination with myo-inositol, potentially confounding results. Observational studies cannot establish causation, and no long-term safety or efficacy data beyond 6 months are available.

Frequently asked

  • What is selenium good for according to research?
    Research suggests selenium is most consistently beneficial for reducing thyroid peroxidase antibody (TPOAb) levels in patients with Hashimoto thyroiditis, with 4 of 5 studies showing positive effects. There is also weaker evidence for reducing thyroglobulin antibodies and increasing free thyroxine levels in thyroid disorders.
  • What dose of selenium is typically used in studies?
    Only one outcome, increased free thyroxine levels, reported a consistent dose of 200 μg per day over about 12 weeks. For other outcomes, no specific dose or form was consistently reported across studies, making dose recommendations unclear from the current evidence.
  • Who benefits most from selenium?
    The strongest evidence comes from patients with autoimmune thyroid conditions, particularly Hashimoto thyroiditis and Graves-Basedow disease. Cognitive function research involved elderly adults aged 60 and older, but the evidence is too weak to conclude who benefits most in that area.
  • Are there caveats or limitations in the research on selenium?
    Yes. The evidence base is small, with only 3–5 studies per outcome. Many studies did not reach statistical significance, and effect sizes ranged from small to large. No long-term data beyond 6 months is available, and one study combined selenium with myo-inositol, which may confound results. Observational studies cannot prove causation.
  • Does selenium help with thyroid antibody reduction?
    For reducing thyroid peroxidase antibodies, the evidence is strong with high consistency across 5 studies. However, for reducing thyroglobulin antibodies, the evidence is weaker: only 2 of 4 studies showed benefit, and effects were small and seen only at 3 months, not at 6 months.

Most-studied combinations with Selenium

most supplement research is combination research
Also studied with:L-Carnitine (2), Saw Palmetto (2), Blood Orange (2), Zinc (6), Copper (2), Iron (3), Vitamin D (8), Vitamin E (4), Vitamin C (2)

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