Selenium is an important trace mineral in the body that is a component of some proteins and is involved in...

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It is recommended that men have at least 55 mcg per day of selenium, which can come from food or supplements. Having too much or too little can be dangerous for your health.

Talk to your healthcare provider if you are concerned about any side effects you experience.


Selenium is a mineral that is involved in several of the body’s processes. More specifically, selenium is an essential trace mineral, meaning that only small amounts are required but that it is vital to the proper functioning of the human body. Selenium is a component of more than 30 proteins that have important roles in the body, including reproduction, the production of DNA and thyroid hormones, and protection against cellular damage and infections. Most of the body’s selenium is stored in skeletal muscle in the form of selenomethionine.

Selenium can be found in a wide variety of foods. Foods containing the most selenium include seafood and organ meat (e.g. kidney and liver). It can also be found in regular meats, eggs, and dairy. Non-animal-based sources of selenium include grains, Brazil nuts (which have a very high amount per serving), rice, beans, bread, spinach, and more. However, while animal-based foods have a predictable amount of selenium, the amount of selenium is plant-based foods varies by location. This is because the amount of selenium in plants is heavily dependent on the amount of selenium in the soil, where selenium originates.

Selenium may play a role in a number of aspects of health:

  • Cancer: Some scientific evidence suggests that consumption of selenium may reduce the risk of certain forms of cancer. However, the Food and Drug Administration has determined that this evidence is limited and not conclusive (3).

  • Cardiovascular disease: Proteins that contain selenium can reduce inflammation and prevent types of blood clots. It is also thought that selenium can protect against the buildup of atherosclerosis in the blood vessels. While several studies have looked into whether selenium can actually protect against cardiovascular disease, more information is still needed (1).

  • Cognition: Studies are mixed, but some have shown that lower levels of selenium are associated with cognitive decline. This may be due to a loss of selenium’s antioxidant activity when levels are lower (1).

  • Immune function: Certain functions of the immune system are impaired in the setting of a selenium deficiency. Additionally, studies have shown a relationship between selenium deficiency and reduced CD4 cell counts in people living with human immunodeficiency virus (HIV) (2).

  • Thyroid disease: The exact role of selenium in the thyroid is unclear, but one possible benefit of supplementation is the reduction of thyroid inflammation, especially thyroid inflammation that occurs in some women after pregnancy, which is called postpartum thyroiditis (2).

According to some studies, selenium also has the following health benefits, which is why it was chosen to be an ingredient in the Roman Dailies:

Prostate Health

Selenium has been shown to have antioxidant properties and plays a role in DNA repair, programmed cell death, and the immune system (1).

The Recommended Dietary Allowance (RDA) of selenium is 55 mcg per day for men and women over the age of 13. For women who are pregnant, 60 mcg per day is recommended, and for women who are breastfeeding, 70 mcg per day is recommended. The RDA represents the daily amount of a mineral that is considered sufficient for 97–98% of healthy individuals.

On the other end of the spectrum, the Tolerable Upper Intake Level (UL) for selenium is 400 mcg per day for both men and women over the age of 13. Repeated intake of amounts greater than the UL can also lead to poor health outcomes (1).

According to 2009–2010 data, most Americans have enough selenium in their diet. The people at risk of having a selenium deficiency include those who are undergoing hemodialysis for kidney failure and those who are living with HIV. It is also possible to be selenium-deficient if you live in a part of the world that has low selenium, especially if you only eat a plant-based diet. China has the areas with the lowest selenium levels in the world but living in certain parts of Europe and New Zealand can also be a risk factor for deficiency. Being deficient in selenium rarely causes overt symptoms but is associated with infertility, a specific form of osteoarthritis, and a disease called Keshan disease, which causes heart problems (1). When symptoms do appear, they can include (2):

  • Skeletal muscle dysfunction

  • Mood disorders

  • Decreased immune function

  • White nailbeds