Selenium is an essential trace mineral that your body builds into around 25 selenoproteins, enzymes that protect cells, activate thyroid hormones and help immune cells work. Its benefits are recognised in six authorised health claims: selenium contributes to normal thyroid function, to the normal function of the immune system, to the protection of cells from oxidative stress, to the maintenance of normal hair and nails, and to normal spermatogenesis. Adults need 60 µg (women) to 70 µg (men) a day, and more is not better: the safe upper level is 255 µg a day.
Key facts about selenium
- Daily need (D-A-CH reference values, 2015): 60 µg for women and 70 µg for men; 60 µg in pregnancy and 75 µg while breastfeeding.
- The nutrient reference value (NRV) on EU and Swiss labels is 55 µg.
- Tolerable upper intake level (EFSA, 2023): 255 µg a day for adults from food and supplements combined, including in pregnancy and breastfeeding.
- Richest source: Brazil nuts, where a single nut can contain roughly 50 to 100 µg, depending on the soil it grew in.
- Soils in much of Europe, including Switzerland, are lower in selenium than in parts of North America, so the selenium content of the same plant food varies widely.
What is selenium good for?
Selenium is good for six things that EU and Swiss authorities have confirmed and allow to be stated. Each one rests on selenoproteins, the enzymes that only work when selenium is built into them.
| Authorised claim: selenium contributes to… | What happens in the body |
|---|---|
| normal thyroid function | Deiodinase enzymes convert the thyroid hormone T4 into its active form T3. The thyroid holds more selenium per gram than any other organ. |
| the normal function of the immune system | White blood cells such as neutrophils, macrophages, natural killer cells and T lymphocytes rely on selenoproteins. |
| the protection of cells from oxidative stress | Glutathione peroxidases neutralise hydrogen peroxide and lipid peroxides before they damage cell membranes. |
| the maintenance of normal hair | Selenoproteins are active in the hair follicle. |
| the maintenance of normal nails | Nail changes are among the first visible signs of both too little and too much selenium. |
| normal spermatogenesis | Selenoprotein GPx4 is a structural part of the sperm midpiece. |
Researchers are also studying selenium status in relation to heart health, cognitive ageing and certain cancers. These are open research questions. Large trials have not shown that selenium supplements protect against these diseases in people who already get enough, so they are not benefits you can expect from taking selenium.
What does selenium do for the body?
Selenium and the thyroid
Your thyroid makes mainly T4, a hormone with little activity of its own. Selenium-dependent enzymes remove one iodine atom and turn it into T3, the form that regulates metabolism in almost every cell. That is why selenium and iodine work as a pair: iodine is the raw material of thyroid hormones and selenium helps activate them. Read more in our article on iodine and the thyroid.
Studies have looked at selenium in autoimmune thyroiditis (Hashimoto's), with mixed results. If you have a thyroid condition, decide on selenium together with your doctor rather than on your own.
Selenium and the immune system
Selenium contributes to the normal function of the immune system. It is one of several micronutrients with this role, alongside vitamins A, C, D, B6, B12, folate, iron and zinc. Our overview of vitamins and minerals for a healthy immune system explains how they fit together, and the article on the benefits of zinc covers selenium's most common partner.
Selenium as an antioxidant
Selenium is not an antioxidant itself, but it is the working part of the glutathione peroxidases, one of the body's main antioxidant enzyme families. Through them, selenium contributes to the protection of cells from oxidative stress, together with vitamins C and E, vitamin B2 and zinc.
Selenium benefits for women
For women, the most relevant roles are thyroid function, the immune system and hair and nails. Thyroid conditions are several times more common in women than in men, which is one reason women search for selenium so often. Women need 60 µg a day, the same in pregnancy, and 75 µg while breastfeeding. If you are pregnant or breastfeeding, follow the advice of your doctor or midwife before adding any supplement.
Selenium contributes to the maintenance of normal hair and nails. Hair loss has many causes, though, from iron and protein status to hormones and stress, and selenium only matters if your intake is low. For a broader look, see our guide to supplements for hair.
Selenium benefits for men
Men need slightly more selenium (70 µg a day). Selenium contributes to normal spermatogenesis, the production of sperm, and protects sperm cells from oxidative stress through the same enzymes as elsewhere in the body. When people search for the "sexual" benefits of selenium, this is the evidence-based part: there is no authorised claim for libido or sexual performance. Zinc, which contributes to normal fertility and reproduction, is the other mineral that matters here; see fertility vitamins for men and women.
The large SELECT trial gave over 35,000 men 200 µg of selenium a day for several years. It found no protection against prostate cancer, and other studies suggest that long-term high doses may be linked to a higher risk of type 2 diabetes. For men, the goal is an adequate intake, not a high one.
Which foods are high in selenium?
Selenium comes from fish, seafood, meat, eggs, nuts, seeds, wholegrains and legumes. The amount in plant foods depends on the soil, so the figures below, from U.S. food tables, are a guide only; European grains tend to contain less.
| Food (portion) | Selenium (approx.) |
|---|---|
| Brazil nuts, 28 g (6 to 8 nuts) | 544 µg |
| Yellowfin tuna, cooked, 85 g | 92 µg |
| Sardines, canned, 85 g | 45 µg |
| Prawns, cooked, 85 g | 42 µg |
| Chicken breast, roasted, 85 g | 22 µg |
| Brown rice, cooked, 1 cup | 19 µg |
| Sunflower seeds, 30 g | 16 µg |
| Egg, 1 large | 15 µg |
| Wholewheat bread, 1 slice | 13 µg |
| Oats, cooked, 1 cup | 13 µg |
| Lentils, boiled, 1 cup | 6 µg |
One portion of Brazil nuts already exceeds the upper level, so keep them for occasional use: one or two nuts are plenty. Finland has added selenium to fertilisers since 1984 because its soils are so poor in it, which shows how much the soil decides what ends up on your plate.
Selenium on a vegan diet
The German Nutrition Society lists selenium as a potentially critical nutrient on a vegan diet, because the main plant sources depend on soil levels and animal foods are excluded. Studies in Europe have found lower selenium intakes in vegans than in people who eat meat or fish. Good plant options are an occasional Brazil nut, sunflower seeds, wholegrains, legumes and mushrooms.
Should you take a selenium supplement?
Most people who eat fish, eggs or meat and plenty of wholegrains get enough selenium from food. A supplement can make sense if your diet is low in selenium, for example on a vegan diet without Brazil nuts. A moderate dose that stays well below the upper level is the sensible choice; high-dose single supplements of 100 to 200 µg are rarely needed without medical advice.
Signs of too little and too much selenium
- Too little: severe deficiency is rare in Europe and mostly seen with kidney dialysis, severe malabsorption or very restricted diets. Changes in hair and nails and a weaker immune response have been described.
- Too much (selenosis): a garlic smell on the breath, a metallic taste, brittle nails, hair loss, skin rashes, tiredness and digestive upset. This usually comes from supplements or from eating many Brazil nuts every day.
Add up all sources, including multivitamins and hair or thyroid products, and stay below 255 µg a day.
Selenium in Sanbera formulas
Daily Essential Women and Daily Essential Men each provide 12.5 µg of selenium per daily serving of three tablets, which is 23% of the NRV. The dose is deliberately moderate: it complements the selenium from your food without approaching the upper level. Selenium contributes to normal thyroid function, to the normal function of the immune system and to the protection of cells from oxidative stress; in Daily Essential Men it also contributes to normal spermatogenesis. Both formulas are vegan and made in Switzerland. The Nightly Reload formulas contain no selenium.
Frequently asked questions
Is selenium good for you?
Yes, in the right amount. Selenium is essential: without it, your body cannot make the enzymes that support thyroid function, the immune system and the protection of cells from oxidative stress. The range between enough and too much is narrow, though. Adults need 60 to 70 µg a day, and regular intakes above 255 µg can cause hair loss, brittle nails and digestive problems.
Why is selenium important for the thyroid?
Selenium is part of the deiodinase enzymes that convert the thyroid hormone T4 into active T3, and of enzymes that protect thyroid tissue from the hydrogen peroxide produced during hormone synthesis. That is why selenium contributes to normal thyroid function. People with a diagnosed thyroid condition should agree any selenium supplement with their doctor.
Is it safe to take selenium every day?
Yes, as long as your total intake from food and supplements stays below the upper level of 255 µg a day. A daily supplement providing around the reference intake or less, such as a multivitamin, is well within that limit. Avoid combining several selenium-containing products with daily Brazil nuts, and speak to a doctor or pharmacist if you take medication.
Can you take selenium and zinc together?
Yes. At normal doses, selenium and zinc do not interfere with each other and are often combined in multivitamins. Both contribute to the normal function of the immune system and to the protection of cells from oxidative stress. High-dose zinc taken for a long time is a separate issue, because it can lower copper absorption.
How many Brazil nuts a day for selenium?
One or two Brazil nuts are enough, and not every day. The selenium content varies widely between nuts, roughly 50 to 100 µg each, depending on the soil. Eating six to eight nuts daily can provide more than twice the upper level of 255 µg, and over weeks this can lead to signs of selenium excess.
Sources
- National Institutes of Health, Office of Dietary Supplements: Selenium, Health Professional Fact Sheet
- EFSA Panel on Nutrition (2023): Scientific opinion on the tolerable upper intake level for selenium
- EFSA Panel on Dietetic Products, Nutrition and Allergies (2014): Dietary Reference Values for selenium
- German Nutrition Society (DGE): Reference values for selenium
- Rayman MP (2012): Selenium and human health, The Lancet
- European Commission: EU Register of nutrition and health claims
This article is for general information and does not replace advice from a doctor or pharmacist. Food supplements are not a substitute for a varied, balanced diet and a healthy lifestyle.