Selenium is an essential mineral, but you need only a small amount of it in your daily diet. Like all minerals, selenium is toxic if you take it in the form of a dietary supplement in excess doses. You can even experience symptoms of chronic selenium toxicity, or selenosis, if you take only a small amount for a long period of time. Selenium toxicity can even be fatal, the Linus Pauling Institute says.
The Basics
The mineral selenium works together with vitamin E as an antioxidant, a substance that protects your cells from the harmful effects of free radicals. It's also important for healthy thyroid and immune system function. The recommended dietary allowance, or RDA, for selenium for adults age 19 and older is 55 mcg a day. According to the Linus Pauling Institute, Americans get 80 to 110 mcg of selenium a day from the foods they eat, on average. Selenium is found in seafood, red meat and food grown in selenium-rich roil. One ounce of Brazil nuts can hold more than 500 mcg of selenium.
Function
Supplemental selenium can be used therapeutically to address selenium deficiency. Solid evidence suggests that it's effective for this purpose. Selenium supplements, when used in conjunction with thyroid hormone replacement, might also be beneficial for people with Hashimoto's thyroiditis. Less evidence supports its use as a way to prevent cancer, heart disease and other medical conditions. According to the Office of Dietary Supplements, selenium toxicity rarely occurs in the U.S.; some documented cases were the result of the manufacturer accidentally making its supplement too strong.
Toxicity
The tolerable upper intake level, or UL, for selenium is 400 mcg a day for adults; this includes the selenium you get from your daily diet. Supplemental selenium in excess of 100 mcg can be harmful to your health, according to the Merck Manuals Online Medical Library. You'll likely notice fast hair loss and brittle nails, as well as other symptoms of selenosis such as nausea, vomiting, diarrhea, tiredness, irritability, skin rash and an unpleasant breath odor. Selenium toxicity can also cause nerve damage.
Cautions
Selenium supplements might not mix well with some medications. Some of these include blood thinners, barbiturates, chemotherapy drugs and drugs that lower cholesterol. Selenium supplements might not be appropriate for people with kidney or stomach problems, notes MayoClinic.com. Most people get more than enough of this mineral from their diet and do not require supplemental selenium. Never self-treat with selenium supplements without first consulting with your treating physician.
References
- Linus Pauling Institute; "Selenium"; J. Higdon; October 2003
- MayoClinic.com: Selenium Supplement (Oral Route)
- Merck Manuals Online Medical Library: Selenium
- University of Maryland Medical Center: Possible Interactions With Selenium
- Office of Dietary Supplements: Selenium
- MedlinePlus Supplements: Selenium
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