Overview
Selenium supplementation at 200mcg/day reduces TPO antibody titers in Hashimoto's thyroiditis, validated across multiple RCTs. Selenium is the essential cofactor for glutathione peroxidase (GPX) and deiodinase enzymes critical to thyroid function and defense.
Mechanism
- Glutathione peroxidase (GPX): Selenium-dependent enzyme that neutralizes H2O2 generated during thyroid hormone synthesis; GPX deficiency leaves thyrocytes vulnerable to oxidative damage (Primitive 4: metal dependencies)
- Deiodinase enzymes: Selenium-dependent T4-to-T3 conversion; deficiency impairs peripheral thyroid hormone activation
- Thioredoxin reductase: Additional selenoprotein involved in thyroid redox balance
Clinical Evidence
Multiple RCTs across European and Asian populations consistently demonstrate:
- Significant reduction in TPO antibody titers at 200mcg/day
- Improved thyroid echogenicity on ultrasound in some studies
- Benefits most pronounced in selenium-deficient populations
Clinical Considerations
- Dose: 200mcg/day is the most studied and effective dose; higher doses risk selenosis
- Form: Selenomethionine and sodium selenite both effective; selenomethionine may have better bioavailability
- Duration: Most studies show benefit by 3-6 months
- Baseline selenium status: Greater benefit in populations with lower baseline selenium intake
- Monitor selenium levels if supplementing long-term