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Selenium

What does the research say about Selenium?

4 health outcomes synthesised

Selenium has been studied for 4 health outcomes, with the strongest evidence supporting its role in reducing thyroid peroxidase antibody (TPOAb) levels in patients with Hashimoto thyroiditis—5 studies show a moderate-to-large effect, including two high-quality meta-analyses. The research predominantly involves clinical populations with autoimmune thyroid conditions, and effective doses are not consistently reported across studies, limiting dose-specific recommendations.

Strongest evidence: The most robust finding is for reduced thyroid peroxidase antibody (TPOAb) levels, with high evidence strength from 5 studies (4 beneficial, 1 neutral). Two meta-analyses showed moderate-to-large statistically significant reductions (e.g., SMD −0.80 at 6 months in a 2025 analysis of 1,610 patients with Hashimoto thyroiditis). Effect sizes are moderate, and effects typically appear at 3–6 months (median study duration 182 days). No consistent dose range was reported across studies.

Mixed or weaker evidence: For reduced thyroglobulin antibody (TgAb) levels, evidence is low—2 of 4 studies were beneficial, but effects were small and significant only at 3 months (not 6 months) in one analysis. Improved cognitive function in elderly adults (aged ≥60) rests on 3 studies: 1 observational study found a small beneficial association, while 2 systematic reviews were neutral; evidence is preliminary. Increased serum free thyroxine levels showed small beneficial effects in 2 of 3 studies (in Hashimoto or Graves-Basedow populations), but a neutral finding from a small RCT in hemodialysis patients suggests benefits may not generalize.

Effective dose patterns: Dose data were not systematically reported across any synthesis, so no cross-cutting dose insights can be drawn from the available evidence.

Population insights: Most research focuses on patients with autoimmune thyroid conditions (Hashimoto thyroiditis, Graves-Basedow disease). The cognitive function data are limited to elderly adults (≥60 years), while the free thyroxine findings are specific to clinical thyroid populations—hemodialysis patients showed no benefit.

Notable caveats: Publication bias is flagged for the TPOAb evidence (null results less likely to be published). Many syntheses are based on small study counts (3–5 papers), so conclusions are preliminary for most outcomes except TPOAb reduction. One TPOAb study used selenium combined with myo-inositol, making it unclear if the neutral result reflects the combination. Observational data for cognition cannot establish causation.

Frequently asked

  • What is selenium good for according to research?
    The strongest evidence supports selenium supplementation for reducing thyroid peroxidase antibody (TPOAb) levels in patients with Hashimoto thyroiditis, with 4 of 5 studies showing beneficial effects and a high evidence strength. Weaker preliminary evidence suggests possible benefits for reducing thyroglobulin antibodies, improving cognitive function in elderly adults, and increasing free thyroxine levels in autoimmune thyroid patients, but results are mixed and based on fewer studies.
  • What dose of selenium is typically used in studies?
    Dose data were not reported consistently across the studies included in any of the syntheses, so no specific dose range can be stated from this evidence. Study durations for TPOAb reduction were typically around 6 months (median 182 days), while free thyroxine studies used a median of 12 weeks (84 days).
  • Who benefits most from selenium?
    Research consistently focuses on patients with autoimmune thyroid conditions, particularly Hashimoto thyroiditis. For TPOAb reduction, all studies enrolled Hashimoto patients (with one also including Graves-Basedow disease). Benefits for free thyroxine were seen in autoimmune thyroid groups but not in hemodialysis patients. Cognitive function findings are limited to elderly adults aged 60 and older.
  • Are there caveats or limitations in the research on selenium?
    Yes. Publication bias is a concern for the TPOAb evidence, as null-result studies are less likely to be published. Most outcomes are based on only 3–4 studies, making conclusions preliminary. The beneficial cognitive finding comes from an observational study, which cannot prove causation. One TPOAb study used selenium combined with myo-inositol, so the neutral result may reflect the combination rather than selenium alone.
  • Does selenium help reduce thyroid peroxidase antibodies?
    Yes, the evidence is strong and consistent. Across 5 studies, 4 showed beneficial effects, and two meta-analyses reported moderate-to-large statistically significant reductions (e.g., SMD −0.80 at 6 months). Effects are typically seen after 3–6 months of supplementation. This is the most well-supported outcome for selenium in the current research.
  • Does selenium improve cognitive function?
    Evidence is preliminary and weak. Only 1 observational study out of 3 found a small beneficial association between selenium levels and cognitive function in elderly adults, while 2 systematic reviews reported neutral findings. The effect size is small, and observational data cannot establish causation, so no firm conclusions can be drawn.

Most-studied combinations with Selenium

most supplement research is combination research
Also studied with:L-Carnitine (2), Saw Palmetto (2), Blood Orange (2), Zinc (5), Copper (2), Iron (3), Vitamin D (8), Vitamin E (4), Vitamin C (2)

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