Selenium is vital to health but only small amounts are needed each day. Moderate doses might provide additional health benefits, but more studies are needed for most of the health claims associated with selenium. In high doses, selenium actually can damage health instead of providing benefits. The level of selenium in food depends on where it comes from, since soil levels of selenium strongly affect the inclusion of this mineral in crops.
Selenium
The trace mineral selenium operates in the immune system and thyroid gland and serves as a powerful antioxidant that protects cells from damage. Healthy teens and adults need only 55 micrograms of selenium per day, and children need even less. Most people get sufficient selenium through foods, mainly through grains grown in regions with soils high in selenium and through meat from animals fed with grains from those regions. In the United States, selenium intake is highest in the Dakotas and Nebraska and lowest in the Pacific Northwest and the Eastern Coastal Plain, although people in these areas still typically get more than the minimum daily recommendation.
Potential Benefits
Selenium at levels higher than the RDA might help protect against some types of cancer. In a 1997 study published in "Biomedical and Environmental Sciences," supplements of 200 micrograms of selenium a day were shown to lower the risk of occurrence and mortality from prostate, lung and colorectal cancers. Other conditions under study that might benefit from increased intake of selenium include arthritis and coronary heart disease. People with HIV also might benefit from selenium and some doctors prescribe selenium supplements as part of a comprehensive HIV treatment plan, according to the NIH Office of Dietary Supplements.
Risks
According to the Institute of Medicine of the National Academy of Sciences, the tolerable upper limit of selenium intake is 400 micrograms per day for adults. People who take too much selenium might experience gastrointestinal problems, fatigue and hair loss, and might become irritable and incur mild nerve damage. People with too much selenium in the bloodstream also might develop bad breath and white blotches on their fingernails and toenails. High levels of selenium might impair fertility in men and increase the risk of bleeding during surgery.
Considerations
Taking less than 200 micrograms per day appears to be safe, but consult a doctor before taking selenium supplements. Remember that the majority of uses for selenium have not yet been sufficiently studied, so this mineral might not be effective for some conditions. It is better to get selenium through food than to take a separate dietary supplement, but be careful about consuming too much. Brazil nuts are extremely high in selenium, with up to 544 micrograms per oz., so it's a good idea to limit your consumption of these nuts.
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