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Selenium

What does the research say about Selenium?

4 health outcomes synthesised

Selenium has been researched for 4 health outcomes, primarily related to thyroid function and cognitive health. The strongest evidence supports its role in reducing thyroid peroxidase antibody (TPOAb) levels, based on 5 studies with moderate effect sizes and high evidence strength in patients with Hashimoto thyroiditis. While a dose of 200 μg per day is noted for increasing free thyroxine levels, most studies lack dose-specific data, limiting precise recommendations.

Strongest evidence

The most robust research area for selenium is reducing thyroid peroxidase antibody (TPOAb) levels. Across 5 studies (4 beneficial, 1 neutral), the evidence strength is high. A 2025 meta-analysis of 1,610 patients found a moderate-to-large statistically significant reduction (SMD –0.80) at 6 months. Effects are seen primarily in patients with Hashimoto thyroiditis, with median study duration of 182 days.

Mixed or weaker evidence

Other outcomes show low evidence strength and small effect sizes. For reducing thyroglobulin antibody (TgAb) levels, 2 of 4 studies were beneficial and 2 neutral, with effects possibly transient (significant at 3 but not 6 months). Improved cognitive function is supported by only one large observational study (neutral in 2 others), making conclusions preliminary. Increasing serum free thyroxine (FT4) levels had small benefits in 2 of 3 studies, with one neutral result in a different population.

Effective dose patterns

Only the FT4 outcome reported a specific effective dose: 200 μg per day over approximately 12 weeks. Other studies did not consistently report dose data, so cross-outcome dose comparisons are not possible.

Population insights

Research predominantly focuses on patients with autoimmune thyroid conditions, especially Hashimoto thyroiditis and Graves-Basedow disease. Cognitive function studies included elderly adults (60+ years), mild cognitive impairment, and stroke survivors, but the evidence is too limited to identify a clear responsive group.

Notable caveats

  • The TPOAb evidence is subject to publication bias, as null results are less likely to be published.
  • For TgAb and cognitive function, much of the evidence comes from small studies or single observational analyses that cannot establish causation.
  • The neutral FT4 study involved hemodialysis patients with nonthyroidal illness syndrome, limiting generalizability to autoimmune populations.

Frequently asked

  • What is selenium good for according to research?
    The strongest research support is for reducing thyroid peroxidase antibody (TPOAb) levels in patients with Hashimoto thyroiditis, where 4 of 5 studies showed beneficial effects with moderate-to-large effect sizes. Selenium may also have small effects on reducing thyroglobulin antibodies and increasing free thyroxine levels, but these findings are based on fewer studies and lower evidence strength.
  • What dose of selenium is typically used in studies?
    Most studies did not report specific doses, but one outcome (increased free thyroxine levels) used 200 μg per day over 12 weeks, showing small beneficial effects. No consistent dose range is available for other outcomes due to lack of reporting.
  • Who benefits most from selenium?
    The research primarily involves patients with autoimmune thyroid conditions, especially Hashimoto thyroiditis and Graves-Basedow disease. For reducing TPOAb, benefits are most consistently observed in Hashimoto patients. Cognitive function studies include elderly adults and those with mild impairment, but the evidence is too mixed to conclude a clear benefit.
  • Does selenium help with cognitive function?
    The evidence is mixed and weak: only 1 of 3 studies (an observational study in adults aged 60+) found a small association between higher blood selenium and better cognitive scores, while 2 found no effect. No randomized controlled trials specifically support selenium supplementation for cognitive improvement.
  • Are there caveats or limitations in the research on selenium?
    Yes. Publication bias is a concern in the TPOAb literature, as null results are underrepresented. For lower-evidence outcomes, conclusions are preliminary due to small study counts, lack of statistical significance, and reliance on observational data. Many studies also fail to report dose information, limiting dose-specific guidance.

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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