Minerals
Selenium
Also called: selenium, selenomethionine
A trace mineral used in antioxidant enzymes and the thyroid.
- Why people take it
- Thyroid health, immunity, cancer prevention.
- What the evidence says
- May lower thyroid antibodies in Hashimoto's. Did not prevent cancer in large trials.
- How it is usually taken
- Usually 50 to 200 mcg a day; the upper limit is 400 mcg. Two Brazil nuts can contain more than a day's need.
- Be careful
- Toxic in high doses (hair loss, brittle nails, garlic breath); adults should stay under 400 µg a day from all sources. Brazil nuts are very high in it.
- Medicines it can interact with
- High doses may add to bleeding risk with blood thinners.
Other minerals
Common questions
What is Selenium?
A trace mineral used in antioxidant enzymes and the thyroid.
Why do people take Selenium?
Thyroid health, immunity, cancer prevention.
Does Selenium work?
May lower thyroid antibodies in Hashimoto's. Did not prevent cancer in large trials.
How much Selenium do people take?
Usually 50 to 200 mcg a day; the upper limit is 400 mcg. Two Brazil nuts can contain more than a day's need.
Is Selenium safe?
Toxic in high doses (hair loss, brittle nails, garlic breath); adults should stay under 400 µg a day from all sources. Brazil nuts are very high in it.
Does Selenium interact with medicines?
High doses may add to bleeding risk with blood thinners.
Sources and further reading
Last reviewed 31 October 2026. Written by Satya Babu.
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