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Selenium – The Antioxidant Trace Element for Thyroid and Immune System
Selenium is an essential trace element that is incorporated as selenocysteine into over 25 selenoproteins. It is indispensable for antioxidant protection, thyroid function, and cellular immune response – and at the same time, it is one of the trace elements with the narrowest window between requirement and toxicity.
Selenoproteins and Their Functions
Selenium acts exclusively through selenoproteins. The most important ones:
| Selenoprotein | Function |
|---|---|
| Glutathione Peroxidase (GPx) | Neutralizes hydrogen peroxide and lipid peroxides → antioxidant protection |
| Thioredoxin Reductase (TrxR) | Regenerates oxidized thioredoxin, DNA repair, apoptosis regulation |
| Iodothyronine Deiodinase (DIO1/2/3) | Activates/inactivates thyroid hormones (T4 → T3 conversion) |
| Selenoprotein P | Selenium transport in blood, antioxidant in endothelial cells |
| Selenoprotein S | ER stress response, inflammation |
Selenium and the Thyroid
The thyroid gland has the highest concentration of selenium of all organs. Without sufficient selenium, deiodinase cannot effectively convert T4 to active T3. Selenium deficiency also promotes Hashimoto's thyroiditis (autoimmune disease of the thyroid) due to weakened antioxidant protection of thyroid cells. Studies show that 200 µg/day of selenium can significantly lower TPO antibody levels in Hashimoto's.
Selenium Status in Germany
Germany is considered a selenium-deficient area: The soils and thus agricultural products contain significantly less selenium than in North American or Brazilian regions. Average intake in Germany: ~35–50 µg/day – below the recommended value of 60–70 µg/day.
Natural Selenium Sources
| Food | Selenium per 100g | Note |
|---|---|---|
| Brazil nuts | 1,917 µg (!) | 1–2 nuts/day are sufficient; more = possible toxicity |
| Tuna (canned) | 80 µg | Good source, but consider heavy metal contamination |
| Pork | 27 µg | – |
| Eggs | 14 µg | Dependent on animal husbandry |
| Broccoli | 1–3 µg | Highly soil-dependent |
| Wheat germ | 79 µg | Soil quality is crucial |
Supplement Forms and Dosage
| Form | Bioavailability | Recommendation |
|---|---|---|
| Sodium selenite (inorganic) | Good (~50–60%) | Inexpensive, but less tissue storage |
| Sodium selenate (inorganic) | Good | Highly water-soluble |
| Selenomethionine (organic) | Very good (~90%) | Incorporated into body proteins; long-term build-up |
| Selenium yeast (organic) | Very good | Mix of selenomethionine and other selenium compounds |
Dosage Recommendation
- Prophylaxis (general): 55–100 µg/day
- For Hashimoto's: 150–200 µg/day (after medical consultation)
- Upper safe limit (EFSA): 300 µg/day (adults)
- Toxicity threshold (chronic): >400 µg/day → Selenium poisoning (selenosis)
Symptoms of Selenium Deficiency and Excess
| Condition | Symptoms |
|---|---|
| Deficiency | Hair loss, brittle nails, muscle weakness, immune deficiency, thyroid problems, Keshan disease (myocarditis in extreme deficiency) |
| Excess (Selenosis) | Garlic odor on breath, hair loss, nail changes, GI complaints, neurological symptoms |
Frequently Asked Questions (FAQ)
How many Brazil nuts are safe?
1–2 Brazil nuts per day cover the daily requirement. More can lead to selenium excess. Do not eat larger quantities daily – selenium content varies greatly depending on origin.
Does selenium help with hair loss?
Selenium supports hair follicle function via GPx enzymes. Hair loss associated with selenium deficiency improves with supplementation. But beware: selenium excess also causes hair loss.
Selenium and cancer prevention?
Earlier studies (NPC study) showed positive effects, later ones (SELECT study) refuted this for high doses. The consensus: adequate supply is important, megadoses are counterproductive.
