Selenium

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 the metabolism.

Why do people take selenium?

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: selenium also seems to 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.

How much selenium should you take?

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 studies to determine if selenium could aid in prostate cancer prevention, men took 200 micrograms daily.

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

 

Group
Recommended Dietary Allowance
Children 1-3 20 micrograms/day
Children 4-8 30 micrograms/day
Children 9-13 40 micrograms/day
Adults and children 14 and up 55 micrograms/day
Pregnant women 60 micrograms/day
Breastfeeding women 70 micrograms/day

 

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Can you get selenium naturally from foods?

Selenium content of food is largely dependent on location and soil conditions, which vary widely. The average daily intake in the U.S. is 125 mcg per day. Populations of the Eastern Coastal Plain and the Pacific Northwest have the lowest selenium levels, averaging between 60 to 90 mcg per day, which is still considered to be adequate intake.

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. 

What are the risks of taking selenium?

  • 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 antacids, chemotherapy drugs, corticosteroids, niacin, cholesterol-lowering statin drugs, and birth control pills.
  • Skin cancer. Selenium supplements are associated with a risk of skin cancer (squamous cell carcinoma), so people at high risk of skin cancer should not take these supplements.
  • Prostate Cancer.  A study by the National Cancer Institute shows that men who already have high concentrations of selenium in their bodies nearly double their risk of aggressive prostate cancer if they take selenium supplements.
  • Diabetes. One study found that people who took 200 micrograms a day of selenium were 50% more likely to develop type 2 diabetes. So far, it's unknown if the selenium actually caused the disease. Discuss the risk with your doctor.
WebMD Medical Reference Reviewed by David Kiefer, MD on December 21, 2016

Sources

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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