Selenium
Silver· human dataAn antioxidant and thyroid mineral with a narrow safe range — more is not better.
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.
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Written and reviewed by Mathew Beale, MSc Biotechnology, University of Reading.
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