Selenium is a dietary mineral you need in small amounts every day. It’s needed for normal thyroid function and it works like an antioxidant to prevent damage to your cells from free radical exposure. Free radicals are by-products of normal oxygen metabolism in your body, and you can be exposed to them through air pollution, smoke and rancid oils. Most people get enough selenium, but certain people are at risk for selenium deficiency.
Sources of Selenium
Selenium is found in plant-based foods, meats and seafood. Brazil nuts, tuna, cod, turkey, grains, beef and walnuts are good sources of selenium. Brazil nuts contain the most per serving, approximately 544 micrograms per ounce of nuts. Selenium content can vary from region to region depending on how much selenium is in the soil where plants are grown. According to the U.S. Office of Dietary Supplements, selenium deficiency is most common in China, where the soil is low in selenium.
The U.S. Institute of Medicine says most adults need 55 micrograms per day, and more for women who are pregnant or breastfeeding. A selenium deficiency might raise your risk for heart disease and weaken your immune system. Low selenium levels might also contribute to hypothyroidism, a disease in which your thyroid hormones are too low, resulting in fatigue, weight gain and feeling cold. The Institute of Medicine also says that selenium deficiency might cause brittle hair and nails and hair loss.
Who’s at Risk for Deficiency?
People who live in areas where soil levels of selenium are low may be at risk for deficiency, but the U.S. Department of Dietary Supplements says that most Americans get enough dietary selenium. People who have severe intestinal diseases such as Crohn’s disease, or have had parts of the stomach surgically removed, may not be able to absorb enough selenium.
You can take selenium supplements to make sure you are getting sufficient amounts. The U.S. Institutes of Medicine set the upper tolerance level at 400 micrograms per day. Regularly taking more than 400 micrograms per day might lead to selenium toxicity. Speak to your health care provider before taking selenium or any other type of dietary supplements.
Sheri Kay has a master's degree in human nutrition. She's the co-author of two books and has been a nutrition and fitness writer since 2004.