Selenium may not be the most recognizable mineral in the supplement aisle (as opposed to, say, calcium, magnesium or iron), but it does play an important role in good health. In the body, selenium is used to form antioxidant enzymes—powerful free-radical fighters that can help prevent conditions such as cancer, heart disease and arthritis.
The most common dietary sources of selenium are plant foods, Brazil nuts, meats and fish. Pasta and white and brown rice are other notable sources. Provided you eat a variety of these types of foods, you should have no problem getting the recommended daily allowance of 55 mcg.
Because the body requires such a small amount of selenium, chances are you don’t suffer from a deficiency—unless you eat a lot of food from certain areas of China or Russia that have low levels of this trace mineral in the soil. There are some exceptions, though: People living with HIV or who suffer from severe gastrointestinal disorders (e.g., Crohn’s disease) may have an increased risk of selenium deficiency. The same is true for those who’ve had part of their stomach surgically removed. And if you’re iodine deficient—rare as it is in the United States—you might also be low in selenium.
If any of the above pertains to you, you could be at risk for lung, colorectal and prostate cancers, heart disease, arthritis, thyroid problems, and even Covid-19. Research suggests, however, that selenium deficiency itself doesn’t cause disease, but rather it can increase the body’s vulnerability to illnesses resulting from other maladies.
If, under the direction of a physician, you decide that you need selenium supplementation, heed the advice of the National Institutes of Health and don’t take in more than 400mcg per day. Excessive blood levels can result in selenium poisoning (selenosis), with symptoms including gastrointestinal upsets, hair loss, white blotchy nails, bad breath, fatigue, irritability and mild nerve damage. (Brazil nuts are extremely high in selenium, so it’s best not to consume too many.)
Truth be told, there’s much to discover about selenium deficiency, not to mention selenium supplementation and how it may or may not be helpful for certain individuals. But at this time, deficiencies seem to be so rare in the United States that researchers aren’t throwing up any red flags.