What selenium does
- Cofactor for deiodinases (T4 → T3 conversion)
- Component of glutathione peroxidase (antioxidant)
- Component of selenoproteins (various roles)
- Immune function support
Thyroid link
The deiodinase enzymes that convert T4 to active T3 are selenium-dependent. Deficiency impairs conversion. Selenium adequacy is also associated with reduced thyroid antibody titers in Hashimoto's.
Optimal ranges
- Optimal serum: 120-180 µg/L
- Below 100: deficient
- Above 250: potentially excessive
Supplementation
- Typical dose: 100-200 µg daily
- Selenomethionine well-absorbed form
- Brazil nuts: 1-2 daily provides adequate intake
- Avoid doses above 400 µg long-term
The clinical pearl: For patients with low free T3 or thyroid antibodies, selenium adequacy is worth checking. 100-200 µg daily often supports thyroid function.
Bottom line
Selenium is essential for thyroid function via deiodinase support. Deficiency impairs conversion. Test and supplement when low.
120-180
µg/L optimal selenium
100-200
µg typical daily dose
Cofactor
for T4 → T3 conversion