Selenium
A trace mineral with antioxidant and thyroid roles — with a narrow safe range.
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What it is
Selenium is a trace mineral that supports antioxidant enzymes and thyroid hormone metabolism. Brazil nuts are a famously concentrated source.
How it works
Selenium is built into antioxidant enzymes (like glutathione peroxidase) and into the enzymes that activate thyroid hormone, giving it central roles in antioxidant defense, thyroid function, and immunity.
What it's been studied for
Used to support antioxidant defenses, thyroid, and immune health, mainly where intake is low.
What the evidence shows
Selenium is essential, but in well-nourished populations deficiency is uncommon and routine supplementation hasn't shown broad benefits. It matters most where soil selenium is low.
Who should consider it
In well-nourished populations, deficiency is uncommon and routine supplementing shows little broad benefit; it matters most where soil selenium is low. A couple of Brazil nuts can supply a day's worth.
Amounts commonly studied
Needs are small (around 55 mcg daily). The gap between enough and too much is narrow.
How to take it
Needs are small (around 55 mcg daily), and the gap between enough and too much is narrow. Selenomethionine is well absorbed. Avoid stacking multiple selenium sources.
Forms & absorption
Selenomethionine is well absorbed. A couple of Brazil nuts can supply a day's worth.
Food sources
Brazil nuts (very concentrated), seafood, meat, eggs, and grains grown in selenium-rich soil.
Safety & interactions
Has a narrow safe range — excess causes selenosis (hair loss, nail changes, nerve issues). Don't stack multiple selenium-containing products.
Myths & what it won't do
Myth: more selenium boosts immunity and prevents disease. Reality: benefits appear mainly when you were deficient, and excess can be harmful. Myth: it's a safe 'more is better' antioxidant. Reality: its therapeutic range is narrow — too much causes selenosis.
Common questions
- Can I just eat Brazil nuts?
- Yes — one or two a day can supply a full day's selenium. Because they're so concentrated, don't overdo them.
- Does it help the thyroid?
- Selenium supports thyroid-hormone metabolism, and it's studied in certain thyroid conditions — but supplement only with guidance if you have a thyroid disorder.
- Can you get too much?
- Yes — its safe range is narrow, and excess causes selenosis (hair loss, nail changes, nerve issues).
The amounts listed here are what published research has used — not a prescription or a recommended dose for you. Confirm anything you plan to take with your own healthcare provider, especially if you take medications, are pregnant or nursing, or have a health condition.
Related goals
Research on Selenium
Recommendations on this page are informed by published research. This is educational information, not medical advice.
- Rayman MP. Selenium and human health. Lancet. 2012;379(9822):1256-1268. View study →Note: Explains that benefits depend on starting status: people who already get enough gain little, and extra selenium may raise type 2 diabetes risk.