Selenium
Selenium (Selenomethionine)
Selenomethionine is the primary organic form of selenium, an essential trace mineral incorporated into selenoproteins including glutathione peroxidases and thioredoxin reductases. It is used to correct selenium deficiency, support thyroid hormone metabolism, and provide antioxidant protection against oxidative stress. Clinically relevant applications include thyroid health optimization, immune support, and potential reduction of certain cancer risks in deficient populations.
Mechanism of Action
Selenium is co-translationally incorporated into selenoproteins via the amino acid selenocysteine, encoded by UGA codons with the assistance of SECIS elements. These selenoproteins include the glutathione peroxidase family (GPx1-4), which neutralize hydrogen peroxide and lipid hydroperoxides, and thioredoxin reductases (TrxR1-3), which regulate cellular redox balance and support DNA synthesis. Selenium also supports deiodinase enzymes (DIO1-3) responsible for converting thyroxine (T4) to the active thyroid hormone triiodothyronine (T3).
Evidence by Health Goal(18 goals)
Dosing Protocols
With meals
The RDA is 55mcg/day for adults; therapeutic supplementation typically ranges from 100-200mcg/day. The tolerable upper intake level (UL) is 400mcg/day. Selenomethionine is more bioavailable (~90%) than inorganic forms such as selenite or selenate. Do not exceed 400mcg/day from all sources combined.
Safety & Side Effects
Selenomethionine is well tolerated at recommended doses of 100-200mcg/day and has a well-characterized safety profile, but the therapeutic window is narrow relative to many minerals — chronic intake above 400mcg/day from all dietary and supplemental sources risks selenosis. Individuals with adequate dietary selenium intake (common in North America) should exercise caution with supplementation, and those with autoimmune thyroid conditions should consult a physician before use.
Possible Side Effects
- !Gastrointestinal discomfort (nausea, diarrhea) at doses above 200mcg/day
- !Garlic-like breath odor due to dimethylselenide exhalation at higher doses
- !Hair thinning or hair loss with chronic excessive intake
- !Nail brittleness or nail loss (selenosis) with prolonged high-dose use
- !Fatigue and irritability at supraphysiologic doses
- !Peripheral neuropathy with severe chronic selenosis (typically >900mcg/day)
- !Metallic taste in the mouth at higher supplemental doses
Interactions
- -May enhance the efficacy of levothyroxine by supporting T4-to-T3 conversion via deiodinase enzymes — monitor thyroid function if co-administering
- -High-dose vitamin C may reduce absorption of inorganic selenium forms, though this effect is minimal with selenomethionine
- -May potentiate the anticoagulant effect of warfarin at high doses by modulating vitamin K-dependent clotting factors — monitor INR
- -Concurrent iodine deficiency may limit the benefit of selenium supplementation on thyroid health — address iodine status concurrently
- -Cisplatin and other platinum-based chemotherapy agents may interact with selenium status — consult oncologist before supplementing during active chemotherapy
Cost & Where to Buy
Generic selenomethionine 200mcg capsules are widely available and inexpensive. Higher costs reflect premium brands, third-party tested products, or combination thyroid support formulas.
Search on Amazon