Supplement · Minerals
Selenium
An antioxidant and thyroid mineral with a narrow safe range: more is not better.
- Evidence
- Silver· human data
- Sources cited
- 1
- Last reviewed
- 22 July 2026
Selenium is a trace mineral built into antioxidant enzymes and thyroid-hormone metabolism. Where soil and diets are low in it, correcting a deficiency supports immune and thyroid function.
The important caveat is its narrow safe range: the gap between enough and too much is smaller than for most nutrients, and chronic excess causes selenosis (hair loss, nail changes, nerve problems). A couple of Brazil nuts can meet needs, so routine high-dose supplements are rarely wise.