Selenium
Trace element for antioxidation, thyroid function, and immune defense
Also known as
Definition
Selenium is an essential trace element incorporated into selenoproteins (e.g., glutathione peroxidases, thioredoxin reductases, deiodinases). It protects cells from oxidative stress, regulates thyroid hormone activation (T4 → T3), and is essential for the immune system. Selenium status varies greatly by region: soils in Germany and Central Europe are selenium-poor, making deficiency common.
| Parameter | Value |
|---|---|
| Unit | µmol/l (µg/l) |
| Reference Range | 0.89–1.65 µmol/l (70–130 µg/l) |
| Optimal Range (lab2go) | 1.15–1.52 µmol/l (90–120 µg/l) (lab2go Optimum Zone; selenoprotein P fully expressed) |
Conversion: 1 µmol/l = 79 µg/l. US labs report in µg/l or ng/ml (normal: 70–150 µg/l).
↓ What a low value means
Selenium deficiency (< 0.89 µmol/l) occurs in selenium-poor regions (Central Europe), with vegan diets, kidney disease, or chronic bowel inflammation. Consequences: increased thyroid risk (Hashimoto's, hypothyroidism), weakened immune system, elevated oxidative stress, muscle pain (Keshan disease with extreme deficiency), elevated TPO antibodies.
↑ What a high value means
Selenium toxicity (> 2.5 µmol/l / > 200 µg/l) results from excessive supplementation or very high consumption of Brazil nuts. Symptoms: selenosis with hair loss, nail changes, garlic breath odor, nerve damage, nausea. The tolerable upper intake level is 300 µg/day (EFSA).
✓ How to optimize this marker
Best source: Brazil nuts (1–2 per day provide 70–90 µg selenium — caution: selenium content varies greatly by origin). Other sources: tuna, salmon, beef, poultry, eggs. Supplementation: 50–100 µg/day selenomethionine (organic form, better bioavailability). For Hashimoto's: 200 µg/day studied in clinical trials.
When to test
With thyroid disease (especially Hashimoto's), vegan diet, chronic inflammatory conditions, or hair loss. Selenoprotein P is a more sensitive marker than serum selenium. Long-term status is better reflected by whole-blood selenium.
Frequently asked questions
Does selenium help with Hashimoto's thyroiditis? +
Multiple randomized trials show that selenium (200 µg/day selenomethionine) reduces TPO antibody titers in Hashimoto's and decreases thyroid inflammation. The European Thyroid Association considers this an adjunctive option for Hashimoto's with selenium deficiency. Check selenium levels before supplementing.
How many Brazil nuts should I eat daily? +
1–2 Brazil nuts daily provide ~70–90 µg selenium, covering the daily requirement. More than 3–4 nuts per day risks excessive selenium intake, as Brazil nuts have the highest selenium content of any food — with wide variation by origin (Brazil > Bolivia).
What is the difference between selenomethionine and sodium selenite? +
Selenomethionine (organic) is better absorbed (~90%) and stored in muscles; it is the preferred form for long-term status maintenance. Sodium selenite (inorganic) has lower absorption (~50%) but acts faster on selenoprotein levels and is used in some Hashimoto's studies.
Is selenium really important for the thyroid? +
Yes. Selenium is essential for the deiodinases that convert thyroxine (T4) into active triiodothyronine (T3). Without adequate selenium, T3 remains low despite normal TSH. Selenoproteins also protect the thyroid from oxidative stress, which plays a role in autoimmune thyroiditis.
Sources
Last Reviewed: May 28, 2026 · sina
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.