What Does Selenium Do in the Body?

Brazil nuts are one of the richest sources of selenium.
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The Institute of Medicine recommends that men get 9.4 milligrams of selenium per day and that most women get 6.8 milligrams; pregnant women should increase their intake to 9.5 milligrams, and breastfeeding women need 10.4 milligrams. Selenium works with proteins to make antioxidant enzymes called selenoproteins, which inhibit free radicals from damaging your cells. Getting an adequate amount of selenium may help prevent heart disease and some types of cancer. It also offers benefits to your thyroid function and immune system.

Cancer Prevention

    A group of researchers from Cornell University published a study in the journal "Biofactors" in 2001 on findings that people who took 200 micrograms of selenium per day showed significantly lower cancer risks than those who did not. Its antioxidant activity appeared to offer protection against the damaging effects of free radicals. Researchers also reported that a selenium intake appeared to prevent the growth of tumors already present.


    Selenium spurs the production of cytokines, molecules that help your body's immune response kick in and boost its ability to fight infection and illness. In 2008, Italian researchers published a study in "Current Pharmaceutical Design," in which they concluded that elderly people who tool zinc and selenium together exhibited a stronger immune system response after receiving the influenza vaccination than people who took a placebo. They called for more studies to be conducted, including studies of elderly people taking zinc plus niacin.

HIV Treatment

    Selenium offers benefits to people with HIV, according to the Linus Pauling Institute. HIV-infected people with low levels of selenium levels are more likely to have severe symptoms and mortality from HIV, but getting enough selenium may enhance the function of the immune system cells that fight HIV. Selenium helps decrease oxidative stress in HIV-infected cells, possibly inhibiting them from replicating. The Linus Pauling Institute cites studies that found that HIV may incorporate selenium into viral selenoproteins that benefit your immune system.

Sources and Bioavailability

    The University of Maryland Medical Center lists brewer's yeast, wheat germ, liver, butter, garlic, whole grains, sunflower seeds and Brazil nuts as good sources of selenium, as well as some types of fish and shellfish, including mackerel, tuna, halibut, flounder, herring, smelt, oysters, scallops and lobster. However, the medical center stresses that the amount of selenium in your food depends on the amount of selenium in the soil in which the food was grown or raised. It also recommends eating whole foods, rather than processed foods, as processing lowers the selenium content in food.


    Most people get approximately 100 micrograms of selenium per day, according to the Linus Pauling Institute, so the average human exceeds his daily value through food. A selenium supplement can benefit you if you are deficient or do not eat an ample amount selenium-rich foods, but avoid taking megadoses of this nutrient. The LPI warns that taking more than 400 micrograms of selenium each day can be fatal. Multivitamin supplements rarely contain more than 70 micrograms per dose.

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