We use essential cookies (authentication, your saved goals/stack) by default. With your permission we’ll also enable privacy-respecting analytics (Vercel Web Analytics, anonymous load-time metrics) and error-replay diagnostics (Sentry — DOM snapshots only when an error fires) so we can fix bugs faster. Learn more about cookies
Selenium (Selenomethionine)
Needed for selenoproteins, including glutathione peroxidase and the enzymes that activate thyroid hormone. Benefits are shown mainly in low selenium status and Hashimoto's antibodies.
What the evidence says
Selenium appears to help in 8 of 9 studies with measurable effects — the evidence leans clearly favourable.
Most evidence is from high-quality meta-analyses and randomised trials published 1981–2026 with a typical study size of 869 participants.
Based on 709 studies · 176 meta-analyses · 399 RCTs · 45,218 total participants
Confidence
High confidenceWhat the studies found
By outcome
Backed by many high-quality meta-analyses showing benefit for Hashimoto's TPO antibodies and thyroid function, but large RCTs found no cancer-prevention benefit and immune effects are inconsistent.
31 trials ongoing or recruiting · 222 completed on ClinicalTrials.gov
20 of the completed trials have posted results
Registered trials show research momentum for Selenium, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Oct 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for Selenium meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
Authorised claims
“Selenium contributes to normal spermatogenesis”
“Selenium contributes to the maintenance of normal hair”
“Selenium contributes to the maintenance of normal nails”
“Selenium contributes to the normal function of the immune system”
“Selenium contributes to the normal thyroid function”
“Selenium contributes to the protection of cells from oxidative stress”
Not authorised by EFSA
“Selenium supports better brain functioning”
“Selenium is necessary for normal cardiovascular function”
“Selenium - Selenium for a healthy prostate - Selenium is beneficial for prostate health”
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
Selenium is an essential trace mineral required for the production of selenoproteins, which have antioxidant and thyroid-regulating functions. Deficiency is uncommon in most developed countries, but low levels can affect thyroid function. No cited trial shows immune benefits from supplements.
Supplementation is most beneficial for those with low selenium status.
Required to make crucial antioxidant enzymes
Critical for thyroid hormone metabolism
How Selenium works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Safe at RDA levels. Stay at or under 255 mcg/day (EU upper limit, the US one is 400 mcg)
Selenium may add to antiplatelet/antioxidant effects; theoretical added bleeding risk at high doses — monitor when combined.
Tip: Take with food
Tip: Reduce dose
Tip: Stop supplementation; indicates excess
Selenium has an evidence score of 6.5/10 — moderate evidence based on 710 indexed studies, including 29 meta-analyses. Needed for selenoproteins, including glutathione peroxidase and the enzymes that activate thyroid hormone. Benefits are shown mainly in low selenium status and Hashimoto's antibodies. Representative study: PMID 23744563.
The commonly studied dose of Selenium is 100-200mcg. Individual needs vary — start at the lower end of the range and adjust based on how you respond.
The best time to take Selenium is with meals. Taking it with food is preferred. Selenium is an essential trace mineral incorporated into selenoproteins (glutathione peroxidases, thioredoxin reductases, deiodinases).
Selenium has a safety rating of "moderate". That is a category, not a measure of individual risk, and there are precautions worth knowing. Reported side effects are uncommon and include GI upset, garlic breath (high doses), hair/nail brittleness (toxicity). Use caution if any of these apply to you: Those with adequate/high selenium status — additional intake risks selenosis (narrow therapeutic window).
Zinc
Likely helpsInvolved in 300+ enzymatic reactions — supports immune defense, testosterone production, wound healing, and sleep quality.
Omega-3
Probably helpsEssential fatty acids critical for brain health, mood regulation, and reducing inflammation throughout the body.
Vitamin D3
Probably helpsHormone-like vitamin that regulates 1,000+ genes — deficiency is widespread and linked to poor immunity, depression, and bone loss.
NAC
Likely helpsRate-limiting precursor to glutathione, the body's master antioxidant — supports mood, respiratory health, and liver protection.
Explore: Best supplements for Men's HealthBest supplements for Women's HealthBest supplements for Vitality & LongevityBest supplements for Focus, Memory & Mood
Reviewed by Dr. Baher Al Hakim · Last reviewed May 2026 · evidence from 709 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
Tap node to isolate • Pinch to zoom • Tap edge for research