Selenium
A trace element that powers key antioxidant enzymes and helps process thyroid hormone. Deficiency is uncommon where soil selenium is adequate but occurs with malabsorption or long-term artificial feeding; too much from supplements is toxic, so both directions matter.
What it measures
Selenium is an essential trace element built into a family of proteins (selenoproteins), including the glutathione peroxidase enzymes that protect cells from oxidative damage and the enzymes that convert thyroid hormone to its active form. The amount in food depends on how much selenium is in the soil where it was grown, so intake varies by region. In areas with adequate soil selenium, deficiency is uncommon; it occurs mainly with malabsorption (such as coeliac or bowel disease), long-term intravenous (artificial) feeding without supplementation, and in regions with very selenium-poor soil, where a severe deficiency historically caused a heart-muscle disease (Keshan disease). Milder deficiency may affect immunity and thyroid function. Importantly, selenium has a narrow safety margin: too much, usually from over-enthusiastic supplementation, is toxic (selenosis), causing hair and nail changes, a garlic breath odour, and nerve and gut symptoms. So both a low and a high level can matter.
What a high value can mean
- Over-supplementation — the commonest cause; selenium supplements taken in excess.
- Selenium toxicity (selenosis) — hair loss, brittle nails, a garlic-like breath odour, nausea, and nerve symptoms. Selenium has a narrow safe range, so a high level from supplements is a real concern.
What a low value can mean
- Malabsorption — coeliac or bowel disease reducing absorption.
- Long-term artificial (intravenous) feeding without selenium.
- Very selenium-poor soil regions — historically linked to a heart-muscle disease (Keshan disease).
- Possible effects — reduced immunity and altered thyroid function.
When to discuss with a doctor
Selenium is a targeted test, not routine. It is worth checking in someone with malabsorption or on long-term artificial feeding who might be deficient, or when selenium toxicity is suspected from high-dose supplements (hair and nail changes, garlic breath, nerve or gut symptoms). Because the safe range is narrow, routine high-dose selenium supplementation in well-nourished people is not recommended and can do harm. Its level is interpreted with the clinical context and albumin. Mediora.AI shows selenium alongside thyroid and related markers so the level is read in context; the interpretation and any supplement change belong with your doctor.