Selenomethionine

amino acid

Take with food

What is it

Selenomethionine is the major form of selenium found in plant and animal foods. It is an amino acid (methionine) with a selenium atom in place of sulfur, and is well absorbed and incorporated into body proteins.

How it works

After absorption, selenomethionine enters the body's general methionine pool and is incorporated nonspecifically into proteins in place of methionine. From this protein pool, it is released as selenium is needed for synthesis of selenoproteins like glutathione peroxidases and thyroid hormone deiodinases. This protein incorporation gives selenomethionine a longer body half-life than inorganic selenium forms, which are used more immediately or excreted. Selenomethionine is the predominant form of selenium in foods like Brazil nuts, fish, and meat.

Evidence for 4 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Correction of selenium deficiency

Grade A

Strong evidence

Effectively raises blood and tissue selenium status, restoring selenoprotein function.

Thyroid antibody reduction in Hashimoto's

Grade B

Good evidence

200 mcg/day of selenomethionine reduces thyroid peroxidase antibodies in some trials; clinical benefit is less clear.

Antioxidant status

Grade B

Good evidence

Supports glutathione peroxidase activity and overall antioxidant capacity.

Cancer prevention

Grade D

Mixed evidence

Earlier observational evidence not confirmed in the SELECT trial.

Dosage

The RDA for total selenium is 55 mcg per day for adults. Selenomethionine supplements typically provide 100 to 200 mcg of selenium. Stay within the tolerable upper limit of 400 mcg per day from all sources.

When and how to take it

Take with food or without — absorption is good either way. Daily consistency matters more than time of day. Avoid stacking selenium from multiple supplements without tracking total intake.

Food sources

Food	Amount	%DV
Brazil nuts, 1 oz	544 mcg selenium	989%
Tuna (yellowfin), 3 oz cooked	92 mcg selenium	167%
Sardines, 3 oz canned	45 mcg selenium	82%
Egg, 1 large	15 mcg selenium	27%
Beef, 3 oz cooked	33 mcg selenium	60%

Safety

Selenomethionine is well tolerated at recommended doses. Like other forms, chronic intake above 400 mcg/day can cause selenosis. Long-term supplementation at 200 mcg/day was associated with increased type 2 diabetes risk in the SELECT trial.

Who should be cautious

Pregnant women should stay near the RDA. People with thyroid disease should discuss with their endocrinologist. Diabetic and prediabetic individuals should consider the SELECT trial findings before long-term high-dose use.

Interactions

Same as other selenium forms. May increase bleeding risk at high doses with anticoagulants. Coordinate with oncologists during chemo or radiation. Some statin/niacin combinations may have HDL effects altered by high-dose antioxidants including selenium.

Frequently asked questions

Is selenomethionine better than other selenium forms?⌄

It has the advantage of incorporating into body proteins and is well absorbed. Inorganic forms (selenite, selenate) also work; for general supplementation, selenomethionine is a common choice.

How much selenomethionine should I take?⌄

100 to 200 mcg of selenium per day is typical. Stay well below the 400 mcg upper limit from all sources.

Does selenomethionine help thyroid problems?⌄

Some trials show reduced thyroid antibodies in Hashimoto's at 200 mcg/day. Discuss with your endocrinologist.

Can I overdose on selenomethionine?⌄

Yes, at chronic high doses (above 400 mcg/day). Symptoms include hair loss, brittle nails, and neurological issues.

Track Selenomethionine with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

Coming to App Store

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.