Selenium: what it is needed for, how much to take and when it is too much
Selenium is a mineral that the body needs in very small amounts – micrograms. That is exactly why it is easy to get either too little or too much.
In this article you will learn what selenium is needed for, how much to take, which foods contain it and how to choose a supplement safely.
In brief. Selenium contributes to normal thyroid function, to the normal function of the immune system, and to the maintenance of normal hair and nails.1 About 70 µg per day is adequate for adults.2 The safe upper limit is 255 µg per day from all sources, and an excess may cause hair loss.3 More is not necessarily better.
What does the body need selenium for?
- contributes to normal thyroid function;1
- contributes to the normal function of the immune system;
- contributes to the protection of cells from oxidative stress;
- contributes to the maintenance of normal hair and nails;
- contributes to normal spermatogenesis (sperm production).
How much selenium do you need per day?
| Indicator | What the sources state | What it means for you |
|---|---|---|
| Adequate intake for adults and pregnant women | 70 µg per day.2 | This amount is enough for most people. |
| Breastfeeding women | 85 µg per day.2 | The requirement is slightly higher. |
| Safe upper limit (UL) | 255 µg per day for adults, including pregnant and breastfeeding women. The limit is lower for children.3 | Selenium from food and from all supplements together is counted. |
| NRV on the label | 55 µg.4 | "364 % NRV" means 200 µg of selenium. |
Example. If you take a 200 µg selenium supplement, a multivitamin containing selenium and also eat a few Brazil nuts, the total amount may exceed the 255 µg limit.
Which foods contain selenium?
Selenium is found in fish and seafood, meat, eggs and dairy products. Among plant foods, Brazil nuts contain the most, while cereals contain less.5
The amount of selenium in plants depends greatly on how much of it is in the soil. For this reason, the selenium content of Brazil nuts varies widely, and a handful of them may provide the entire daily requirement.5
Do you need a selenium supplement?
A supplement may be useful if you rarely eat fish, meat and eggs, for example if you follow a vegan diet. However, a higher dose does not mean greater benefit.
Example. In one of the largest selenium studies, men took 200 µg of selenium per day for several years – almost three times more than needed. The researchers expected this to reduce the risk of certain diseases, but no such benefit was found.⁶ Therefore, if you get enough selenium from food, a high-dose supplement is not necessary.6
Which form of selenium should you choose?
| Form | What is worth knowing | What it means for you |
|---|---|---|
| L-selenomethionine | An organic form similar to the one found in food. It was also used in the large study mentioned above.6 | The most common form in supplements. |
| Selenium yeast | Yeast grown in a medium containing selenium. | Not suitable for people with a yeast allergy. |
| Sodium selenite | An inorganic form. | Often used in multivitamins and liquid forms. |
Side effects and safety of selenium
When too much selenium is taken for a long time, hair loss may be the first sign.3 Therefore, stick strictly to the upper limit.
Consult your doctor first if:
- you have a thyroid disease or take medicines for it;
- you are pregnant or breastfeeding;
- you want to give a supplement to a child – the upper limit is lower for children;3
- you have a kidney disease or take other medicines.
A supplement is not a substitute for a varied diet.7
Selected selenium products
Commercial information. The products listed here are available in our shop. This is not a ranking of effectiveness. Before buying, check the composition and instructions for use on the product page.
Selenium, 100mcg - 100 tablets - NOW Foods
L-selenomethionine, 100 µg of selenium per tablet. The manufacturer recommends 1–2 tablets per day – choose the lower dose if you also get selenium from food.8
SelenoExcell Selenium - 200mcg - 60 capsules - Swanson
Selenium from selenium yeast, 200 µg per capsule (286 % NRV). Take 1 capsule per day. Add up the selenium from multivitamins.9
Selenium Oral Spray, 200mcg (Pineapple) - 25 ml - Osavi
Under-the-tongue spray with sodium selenite, 200 µg per spray. Convenient for those who find it difficult to swallow tablets.10
Selenium - 100 mcg - 200 Capsules - Swanson
L-selenomethionine, 100 µg of selenium per capsule, pack of 200 capsules. The manufacturer recommends 1–2 capsules per day.11
Frequently asked questions
Does selenium help the thyroid?
Selenium contributes to normal thyroid function.1 However, if you have a thyroid disease, take a supplement only after consulting your doctor.
How many Brazil nuts can you eat?
Their selenium content varies greatly, so there is no exact number.5 If you eat Brazil nuts every day, you usually do not need a selenium supplement.
Can selenium be taken together with multivitamins?
It can, but add up the total amount of selenium. From food and all supplements together, it should not exceed 255 µg per day.3
Scientific sources
- Komisijos reglamentas (ES) Nr. 432/2012, kuriuo nustatomas leidžiamų teiginių apie maisto produktų sveikatingumą sąrašas (konsoliduota redakcija). EUR-Lex
- EFSA NDA Panel. Scientific Opinion on Dietary Reference Values for selenium. EFSA Journal. 2014;12(10):3846. doi:10.2903/j.efsa.2014.3846
- EFSA NDA Panel. Scientific opinion on the tolerable upper intake level for selenium. EFSA Journal. 2023;21(1):7704. doi:10.2903/j.efsa.2023.7704
- Reglamentas (ES) Nr. 1169/2011 dėl informacijos apie maistą teikimo vartotojams, XIII priedas. EUR-Lex
- EUFIC. Selenium: foods, functions, how much do you need & more. eufic.org
- Lippman SM, Klein EA, Goodman PJ et al. Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2009;301(1):39–51. doi:10.1001/jama.2008.864
- Direktyva 2002/46/EB dėl valstybių narių įstatymų, susijusių su maisto papildais, suderinimo. EUR-Lex
- NOW Foods. Selenium, 100 µg, 100 tablets. Product label.
- Swanson. SelenoExcell Selenium, 200 µg, 60 capsules. Product label.
- Osavi. Selenium Oral Spray, 200 µg, 25 ml. Product label.
- Swanson. Selenium, 100 µg, 200 capsules. Product label.
Disclaimer. This article is for informational purposes only and does not replace consultation with a doctor or pharmacist. Food supplements are not intended to treat or prevent diseases and are not a substitute for a varied diet and a healthy lifestyle. Before taking supplements, especially during pregnancy or breastfeeding, if you have a chronic condition or if you take medicines, consult a healthcare professional.
