BiomarkersSelenium

Minerals

Selenium

Antioxidant mineral that helps make thyroid hormone

On your report it may say: Serum selenium, Plasma selenium

Selenium is part of antioxidant enzymes and helps convert thyroid hormone into its active form. The gap between enough and too much is small, so testing helps before taking high doses.

Updated 2026-10-26

Typical ranges · µg/L

Low below 70
In range 70–150
High 150+

µmol/L = µg/L × 0.0127

Whole blood and serum selenium have different ranges; check which your lab used.

Ranges vary by lab, age and sex. The range printed on your report applies.

If it's low

Selenium may be too low for antioxidant and thyroid function.

Common causes

  • Low-selenium soil and diet
  • Gut absorption problems
  • Kidney dialysis

What you might notice

  • Usually subtle
  • Tiredness
  • Weak immunity

If it's high

High selenium is almost always from supplements or Brazil nuts and can be toxic.

Common causes

  • Supplements
  • Eating many Brazil nuts

What you might notice

  • Hair loss
  • Brittle nails
  • Garlic smell on the breath

Testing

Who should test
People with thyroid conditions considering selenium, or with very limited diets.
How to prepare
No fasting needed usually; follow your lab's instructions.
When to retest
3 months after a change.

What can help

Food sources

Brazil nuts (1–2 is enough)EggsFishSunflower seedsMushrooms

See a doctor if levels are high or you have hair or nail changes.

Common questions

Can TSH tell me my selenium?

No. Thyroid tests don't measure selenium.

How many Brazil nuts is safe?

One or two a day; their selenium varies a lot.

Explore further

When to take them

Sources

  1. NIH Office of Dietary Supplements: Selenium fact sheet for health professionals

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For general education only, not medical advice. Ranges shown are typical for adults; the range printed on your lab report applies. Talk to a qualified doctor about your results.