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Selenium (Selenomethionine)
Required for selenoprotein production that regulates thyroid hormones, powers glutathione peroxidase, and strengthens immune defense.
What the evidence says
Selenium appears to help in 19 of 23 studies with measurable effects — the evidence leans clearly favourable.
Most evidence is from high-quality meta-analyses and randomised trials published 2008–2026 with a typical study size of 230 participants.
Based on 133 studies · 38 meta-analyses · 13 RCTs · 211,631 total participants
Confidence
HighWhat the studies found
By outcome
Selenium has an evidence score of 9/10 — very strong evidence based on 131 indexed studies, including 31 meta-analyses. Required for selenoprotein production that regulates thyroid hormones, powers glutathione peroxidase, and strengthens immune defense.
The commonly studied dose of Selenium is 100-200mcg. Research points to an estimated optimal dose around 200mcg, with a minimum effective dose near 100mcg. Individual response varies — start low and adjust.
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).
Last reviewed May 2026 · evidence from 39 studies · how we score
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.
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 suboptimal levels may affect thyroid function and immune health. 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.
100-200mcg
Take with food
| Form | Type |
|---|---|
| 💊Selenomethionine (best absorbed) | Recommended |
| 💊Selenium yeast | Alternative |
| 💊Sodium selenite | Alternative |
Selenomethionine is the most bioavailable organic form.
Minimum: 4 weeks
Optimal: weeks
Cycling: Not required
Note: Take with food for better absorption. Do not exceed 400mcg/day from all sources.
You can get selenium from these foods and drinks. Doses are typical per-serving estimates — actual content varies by brand, brew, cooking, etc.
70 mcg per piece
1 nut ≈ 70 mcg = ~127% RDA. Don't eat more than a few per day — selenium toxicity at sustained high intake.
Based on Cochrane systematic review showing moderate-certainty evidence for TPO antibody reduction. Effects on thyroid hormone levels (TSH, T4, T3) were inconsistent across studies.
Supports healthy thyroid hormone levels
Supports immune cell activity
Safe at RDA levels; don't exceed 400mcg
May interact; consult oncologist
May affect cholesterol-lowering effects
Tip: Take with food
Tip: Reduce dose
Tip: Stop supplementation; indicates excess
Both support immune function and antioxidant defense
Enhanced immune and antioxidant support
Selenium is required for thyroid hormone conversion
Optimal thyroid function — don't supplement iodine without adequate selenium
Both support glutathione antioxidant system
Enhanced antioxidant defense
Selenium is generally safe at recommended doses, with a few precautions worth noting. The most commonly reported side effects are 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; Thyroid conditions (hypothyroidism, hyperthyroidism, Hashimoto's, Graves' disease) — selenium affects thyroid hormone metabolism and may alter thyroid function; consult endocrinologist before use.
NAC
Likely helpsRate-limiting precursor to glutathione, the body's master antioxidant — supports mood, respiratory health, and liver protection.
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