Quick answer

Selenium is a trace mineral your body builds into 25 selenoproteins, which the thyroid gland, sperm and the cell's antioxidant defenses rely on. Adults need 55 mcg a day, and most Americans get more than that from food. Taking more than 400 mcg a day for long periods can cause hair loss and brittle nails.^1,2

Key facts

The thyroid gland holds a higher concentration of selenium than any other organ in the body.²
Average intake in the United States is 108 mcg a day from food and drink, about twice the 55 mcg adults need.²
A single Brazil nut can hold 68 to 91 mcg, more than a full day's need.¹
In people who already get enough, extra selenium did not raise the selenoproteins that do its work.^2,3
The adult upper limit is 400 mcg a day from all sources, and Europe's food safety agency set a lower limit of 255 mcg.^1,4

What selenium does

Selenium is part of 25 selenoproteins in the human body.²

Those proteins do the work. The glutathione peroxidases and thioredoxin reductases protect cells from oxidative damage, including the hydrogen peroxide the thyroid makes while it produces its hormones. Other selenoproteins convert the thyroid hormone T4 into its active form, T3, and one is a structural part of mature sperm. NIH adds that selenium is needed to make DNA.^1,2

Between 28% and 46% of the body's selenium is in skeletal muscle.²

The body absorbs selenium from food readily, and how much it takes in does not depend much on how much it already has. It keeps its level steady mainly by passing the excess in urine, and at higher intakes also through the breath and stool. That is why blood selenium mostly reflects what you ate recently, while hair and nails record months or years.²

What the evidence shows

Each statement below describes a normal role of selenium and carries a grade, with the amount the evidence refers to. These roles depend on getting enough. In studies of people who already had enough selenium, taking more did not raise the selenoproteins that were measured.^2,3

Contributes to normal thyroid function*^1,2

Moderate evidence

NIH describes selenium as a nutrient the thyroid gland needs to make its hormones and work properly, and selenoproteins convert the hormone T4 into its active form, T3. The thyroid holds a higher concentration of selenium than any other organ. This describes getting enough: in a 6-month trial in 368 healthy adults aged 60 to 74, taking 100, 200 or 300 mcg a day raised blood selenium but did not change thyroid function.

Amount studied: Recommended intake of 55 mcg a day for adults, from food and supplements

Contributes to normal immune function*^1,2,5

Moderate evidence

NIH lists helping the body resist germs among the jobs selenium is needed for, and the European Union's list of permitted nutrient statements, drawn up after review by the European Food Safety Authority, includes normal immune function for selenium. It describes what enough selenium does, not an effect of taking more than you need.

Amount studied: Recommended intake of 55 mcg a day for adults, from food and supplements

Contributes to the protection of cells from oxidative stress*^1,2,3

Moderate evidence

Glutathione peroxidases and thioredoxin reductases, two families of selenoproteins, protect cells from oxidative damage, and NIH lists protecting cells among the reasons the body needs selenium. More selenium does not seem to add more of this protection: in adults who were not short of selenium, about 200 to 600 mcg a day for 16 weeks did not raise glutathione peroxidase activity or selenoprotein P.

Amount studied: Recommended intake of 55 mcg a day for adults, from food and supplements

How much you need

Adults and teens 14 and older need 55 mcg of selenium a day from all sources.¹

The recommended amount rises to 60 mcg a day in pregnancy and 70 mcg a day while breastfeeding.¹

Average selenium intake in the United States is 108 mcg a day from food and drink and 116 mcg with supplements. Men average 132 mcg a day from food and drink, and women 94 mcg.²

So most people do not need a separate selenium supplement. Those who may get too little include people whose diet is mostly plant foods grown in low-selenium soil, as in parts of China, and people on long-term kidney dialysis. People who eat vegan diets and people who smoke also tend to have lower levels.^1,2

Where selenium comes from

Brazil nuts are the richest source, with an average of 544 mcg per ounce (6 to 8 nuts), or 68 to 91 mcg per nut, though other analyses vary widely.^1,2

Seafood, meat and poultry are rich sources: 3 ounces of cooked yellowfin tuna has about 92 mcg, canned sardines 45 mcg, cooked shrimp 42 mcg, and a broiled pork chop or roasted beef steak 37 mcg.²

The selenium in plant foods depends on the soil they grew in, so it varies widely from region to region; meat and other animal foods vary much less.²

Because selenium is bound to protein in food, protein-rich foods tend to be the best sources. The guide to foods high in selenium has a fuller list with amounts per serving.²

Forms and amounts in supplements

Supplements use selenomethionine, selenium-enriched yeast, sodium selenite or sodium selenate, and the body absorbs up to about 90% of the selenium from each of them.^1,2

Many multivitamins contain 55 mcg of selenium. Products that pair selenium with vitamin E or a few other ingredients usually have 50 to 200 mcg, and selenium-only supplements 100 to 400 mcg.²

The Supplement Facts panel gives the amount of selenium itself, in micrograms. A single-ingredient product with 200 mcg supplies more than three days of an adult's need before any food is counted.¹

What's in ours

What’s in ours

Men's Multi: Selenium, 30 mcg per serving, from the label

Side effects, medicines and who should ask first

Getting too much selenium over time (selenosis) can cause garlic breath, a metallic taste in the mouth, hair loss, brittle nails or nail loss, skin rash, nausea, diarrhea, extreme tiredness, irritability and nervous system problems.^1,2

The upper limit for selenium is 400 mcg a day for adults and teens 14 and older, including during pregnancy and breastfeeding, counting food, drinks and supplements together. It is lower for children: 90 mcg at ages 1 to 3, 150 mcg at 4 to 8 and 280 mcg at 9 to 13. The limits do not apply when a doctor is giving selenium.^1,2

In SELECT, a trial in 35,533 men aged 50 and over, 200 mcg a day did not lower the risk of prostate cancer. In men whose selenium levels were already high, supplements were linked with more high-grade prostate cancer, and the researchers advised men over 55 to avoid selenium supplements above recommended intakes.²

Ask your pharmacist or doctor first

Cisplatin, a chemotherapy medicine used for several cancers, can lower selenium levels in the blood and hair, and it is not known whether that matters for health. NIH reports that studies of selenium taken during cisplatin treatment are small, and that a Cochrane review found the evidence insufficient to judge them. Ask your cancer care team before taking selenium during chemotherapy.^1,2

Reported in studies

Ask your doctor first if you have a thyroid condition or take thyroid medicine
Ask first if you are pregnant or breastfeeding, especially if you have thyroid antibodies²
Ask first if you have kidney disease or are on dialysis
Count Brazil nuts and every supplement that contains selenium toward the upper limit¹

Questions people ask

Is selenium good for your hair or skin?

We found no trial showing that extra selenium does anything for hair or skin in people who already get enough. Hair loss, brittle nails and skin rash are among the signs of getting too much, and Europe's food safety agency based its upper limit on hair loss.^1,4

What does selenium do for men?

Men need the same 55 mcg a day as women. Selenium is part of a protein built into sperm, but in a 48-week trial in healthy men, 300 mcg a day did not change sperm concentration or motility. Researchers from the largest trial advised men over 55 not to take selenium supplements above recommended intakes.^1,2

Do I need a selenium supplement?

Most people in the United States do not. Average intake from food is about twice the recommended amount, deficiency is very rare here, and many multivitamins already include 55 mcg.^1,2

See what we make

Every product shows its whole label and what its lab report covers. The store opens soon.

See the Full Measure line Men's Multi

Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.