Medically Reviewed by Jennifer Robinson, MD on May 01, 2023

Selenium is a mineral found in the soil. Selenium naturally appears in water and some foods. While people only need a very small amount, selenium plays a key role in their metabolism.

Selenium has attracted attention because of its antioxidant properties. Antioxidants protect cells from damage. Evidence that selenium supplements may reduce the odds of prostate cancer has been mixed, but most studies suggest there is no real benefit. Selenium does not seem to affect the risk of colorectal or lung cancer. But beware: some studies suggest that selenium may increase the risk of non-melanoma skin cancer.

Among healthy people in the U.S., selenium deficiencies are uncommon. But some health conditions -- such as HIV, Crohn's disease, and others -- are associated with low selenium levels. People who are fed intravenously are also at risk for low selenium. Doctors sometimes suggest that people with these conditions use selenium supplements.

Selenium has also been studied for the treatment of dozens of conditions. They range from asthma to arthritis to dandruff to infertility. However, the results have been inconclusive.

The recommended dietary allowance (RDA) includes the total amount of selenium you should get from foods and from any supplements you take. Most people can get their RDA of selenium from food.

In some studies to determine if selenium could aid in prostate cancer prevention, men took 100 micrograms daily.

The safe upper limit for selenium is 400 micrograms a day in adults. Anything above that is considered an overdose.


Recommended Dietary Allowance
Children 1-320 micrograms/day
Children 4-830 micrograms/day
Children 9-1340 micrograms/day
Adults and children 14 and up55 micrograms/day
Pregnant women60 micrograms/day
Breastfeeding women70 micrograms/day


Selenium content of food is largely dependent on location and soil conditions, which vary widely.

Good natural food sources of selenium include:

  • Nuts, like Brazil nuts and walnuts
  • Many fresh and saltwater fish, like tuna, cod, red snapper, and herring
  • Beef and poultry
  • Grains

Whole foods are the best sources of selenium. The mineral may be destroyed during processing. 

  • Side effects. Taken at normal doses, selenium does not usually have side effects. An overdose of selenium may cause bad breath, fever, and nausea, as well as liver, kidney and heart problems and other symptoms. At high enough levels, selenium could cause death.
  • Interactions. Selenium may also interact with other medicines and supplements, such as some antacids, chemotherapy drugs, corticosteroids, niacin, cholesterol-lowering statin drugs, and birth control pills.
  • Skin cancer. Selenium supplements may be associated with a risk of skin cancer (squamous cell carcinoma), so people at high risk of skin cancer should not take these supplements.

Show Sources

Longe, J., ed. The Gale Encyclopedia of Alternative Medicine, second edition, 2004.
Natural Standard Patient Monograph: "Selenium."
Office of Dietary Supplements: "Selenium."
WebMD Health News: "Selenium Supplements: Diabetes Risk?"
Combs, G. The British Journal of Nutrition, 2001.
Rayman, M. Lancet, 2000.
Schrauzer, G. Journal of Nutrition and Metabolism, 2000.

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