Selenium

Trace mineral

What does Selenium do in your body?

Built into selenoproteins that protect cells from oxidative damage and activate thyroid hormone.

What does Selenium do?

Part of glutathione peroxidases (antioxidant defense) and deiodinases (thyroid hormone activation).

Where does Selenium act in the body?

Thyroid, immune cells, every cell.

Which foods contain Selenium?

Brazil nuts (one nut can exceed the RDA), seafood, meat, eggs, grains (varies by soil).

How much Selenium do adults need?

RDA: 55 mcg for adults. Upper limit: 400 mcg.

What happens with too little Selenium?

Rare where soils contain selenium.

Can you get too much Selenium?

Hair and nail loss, garlic breath. Eating several Brazil nuts every day can exceed the upper limit.

What does Selenium interact with?

Works with iodine for thyroid function.

What is known and unknown about Selenium?

Large trials (e.g., SELECT) found selenium supplements didn't prevent prostate cancer.

Evidence & sources

• The adult RDA for selenium is 55 mcg/day; the UL is 400 mcg. Evidence: regulatory. Known: Set by the Institute of Medicine (2000). Unknown: — Source: NIH Office of Dietary Supplements, Selenium — Health Professional Fact Sheet (Current revision).

Connected topics

• Thyroid
• Iodine
• Brazil Nuts

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General education only, not medical advice. Drafted Oct 2026 · pending qualified expert review.