Selenium (Se)

What is selenium?

Selenium is a mineral that helps protect our cells against damage and supports our overall health and wellbeing. It is an essential trace mineral, meaning we require it in small amounts. Since we cannot produce selenium in our bodies, we must get this nutrient through food.

Why we need it

One of the main functions of selenium is supporting antioxidant enzymes, which are enzymes that protect against cellular damage. For example, selenium is an essential component of glutathione peroxidases, which are a family of enzymes that break down harmful substances called free radicals.¹ In this way, these antioxidant enzymes help defend against oxidative stress, a phenomenon that can contribute to a wide range of diseases.

We also need selenium to make thyroid hormones, which are hormones that regulate our metabolism (the process through which we make and use energy for bodily functions). Specifically, selenium is an essential component of deiodinases, which are enzymes that activate thyroid hormones.¹

Selenium is required by many other enzymes as well, including enzymes that support immune function, growth and development, and heart health, among other things.¹

Where it’s found

Selenium is naturally present in many foods, including meats, seafood, grains, legumes, and dairy products. Examples of selenium-rich foods include:

Organ meats
Tuna fish
Nuts and seeds
Yogurt
Cottage cheese
Breakfast cereals
Eggs
Salmon
Enriched pasta

Selenium is also available as a dietary supplement, either on its own or as part of a multivitamin. There are many forms of supplemental selenium, including selenomethionine, selenate, selenite, and even selenium-enriched yeast.² Selenomethionine and selenium-enriched yeast appear to be absorbed more efficiently in the body compared to selenate or selenite.³

Daily requirements

The daily Recommended Dietary Allowance (RDA) for selenium, or the amount that is likely to meet the needs of most healthy people, is 20 micrograms (mcg) for children aged 1-3 years, 30 mcg for children aged 4-8 years, 40 mcg for children aged 9-13 years, and 55 mcg for adults and adolescents aged 14 years and up.⁴ For pregnant or breastfeeding women, the RDA increases to 60 mcg and 70 mcg, respectively.

Selenium deficiency

Selenium deficiency can have serious health consequences. It can cause Keshan’s disease, a condition characterized by heart failure and heart arrhythmias.⁵ Selenium deficiency can also cause Kashin-beck disease, a type of osteoarthritis (a disease that causes bone and joint dysfunction).⁵ Additionally, selenium deficiency may impair our immune function, increasing the risk of infection and autoimmune diseases.^{6, 7}

Selenium deficiency is common in regions of the world where the selenium content in soil is low, such as China, Russia, and New Zealand.⁶ In other areas, such as the United States and Canada, selenium deficiency is rare.

Can you get too much selenium?

Selenium can be toxic when consumed in large amounts. Symptoms of selenium toxicity include brittle nails, hair loss, garlic-smelling breath, fatigue, and digestive issues. Consuming extremely high doses of selenium (gram amounts) can be fatal.⁴

To prevent toxicity, a Tolerable Upper Intake Level (UL) has been established for selenium. The UL for selenium is 400 mcg for adults.⁴ This value represents the maximum daily amount that is unlikely to cause toxicity.

Fun facts

Brazil nuts are by far the richest dietary source of selenium. You can meet your daily selenium needs with just a single brazil nut, which provides about 96 mcg of selenium.⁸

Selenium is named after selene, the Greek word for “moon”. This is because, when selenium was discovered, it was found to be very similar to tellurium, an element that means “Earth” in Latin. So, selenium was named after the moon to reflect this similarity.⁹