Selenium
Selenium is an essential trace mineral that plays a vital role in thyroid physiology and immune regulation. It is required for the enzymatic conversion of thyroxine (T4) into the active form triiodothyronine (T3) via selenoenzyme deiodinases.
Dietary Sources
- Brazil nuts (very high — a few per day can meet daily needs)
- Tuna, sardines, halibut, shrimp
- Eggs (note: egg yolks are also high in iodine)
- Legumes (beans, chickpeas, lentils)
- Meats (beef, chicken, pork)
- Fortified pasta, cereals, brown rice, oatmeal
- Mushrooms
Recommended Daily Amount
55 mcg/day for adults (U.S. RDA). Excess selenium is toxic; doses >300 mcg/day have been shown to increase all-cause mortality rates.
Role in Thyroid Disease
Graves’ Disease and Thyroid Eye Disease (Graves’ Orbitopathy)
- A large European clinical trial showed that six months of selenium supplementation had a significant beneficial effect on thyroid eye disease (Graves’ orbitopathy), with improvements in quality of life persisting at 12 months and no side effects.
- Some trials show selenium reduces thyroid antibody levels in graves-disease patients.
- However, selenium does not appear to directly improve thyroid function test results (TSH, FT4, FT3).
- Among patients on antithyroid medications, selenium supplementation may normalise thyroid levels more quickly.
Hyperthyroidism Generally
- Selenium supports overall thyroid function and may help reduce autoimmune disease activity.
Cautions
- Do not exceed recommended doses; high-dose supplements (>300 mcg/day) are associated with increased mortality.
- Some selenium-rich foods (tuna, halibut, shrimp, egg yolks) are also high in iodine — may conflict with low-iodine-diet requirements.