Selenium — Supplements
Essential trace mineral serving as a cofactor for selenoproteins involved in antioxidant defense and thyroid metabolism.
Overview
Selenium is an essential trace element incorporated into selenoproteins including glutathione peroxidases (GPx), thioredoxin reductases, and iodothyronine deiodinases critical for antioxidant defense, thyroid hormone conversion (T4 to T3), and immune function. Selenium status varies globally depending on soil content. The SU.VI.MAX trial and other studies suggest adequate selenium status is associated with reduced cancer risk and improved immune function. However, the SELECT trial showed no benefit and potential harm from selenium supplementation in selenium-replete individuals.
Indications
- Thyroid function support (T4 to T3 conversion)
- Antioxidant defense via selenoproteins
- Immune function optimization
- Autoimmune thyroiditis management (adjunctive)
Mechanism of Action
Selenium is incorporated as selenocysteine (the 21st amino acid) into 25 human selenoproteins
Dosing
| Compound | Dose | Frequency | Notes |
|---|---|---|---|
| Selenium (as selenomethionine) | 200 mcg | Once daily | Selenomethionine or selenium yeast preferred; do not exceed 400 mcg/day total |
Safety & Contraindications
- Narrow therapeutic window; toxicity (selenosis) at >400 mcg/day
- Selenosis symptoms: garlic breath, brittle nails, hair loss, GI distress
- SELECT trial showed increased prostate cancer risk at 200 mcg/day in selenium-replete men
- Assess selenium status before supplementing; avoid if already adequate