Selenium may offer health benefits such as cancer protection, lowering risk of heart disease and reducing the risk of Alzheimer's disease.

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Selenium may have caught your attention, as it’s one among many supplements that has been studied for its potential to treat a variety of conditions ranging from asthma and dandruff to infertility. While it’s true that our bodies need this essential to function properly, it takes very little to do the job. Most healthy Americans are not at risk for deficiency if we’re eating a diet that includes a variety of healthy foods. In fact, just one Brazil nut each day provides more than the recommended amount. Some people have low levels and need to supplement selenium, and it may play a role in additional health benefits, though the evidence for people with adequate levels shows potential, but is so far inconclusive.

Benefits of Selenium | Sources of Selenium | Selenium Supplements

What is Selenium?

Selenium is a trace mineral found naturally in the soil, water, and in certain (mostly whole) foods, including Brazil nuts, tuna, and eggs. An essential mineral, our bodies need selenium to properly function. Because our bodies do not make selenium, we must get it through diet. Though we only need small amounts of this mineral, it plays an important role in several bodily processes, including metabolism and thyroid function. Selenium is also necessary to make proteins that help the cells function and, as an antioxidant, it can help protect cells against harmful free radicals and repair damaged cells.

Potential Benefits of Selenium

Selenium is indeed essential for optimal body function and health, and it may play a role in other important aspects of our health as well. Researchers have studied and continue to study this nutrient to determine its potential to impact health, disease prevention, and well-being. Here are some areas of particular interest:

Cancer Protection: Selenium has been associated with lowered risk of some cancers, which may be due to its antioxidant activity, helping reduce oxidative stress, boost immunity, and fight cancer cells. One review of 69 clinical studies found that higher levels of selenium in the blood were associated with reduced risk of breast cancer, lung cancer, esophageal cancer, gastric cancer, and prostate cancer.

Heart Health: As an antioxidant, selenium may help reduce oxidative stress and inflammation, and may help decrease the risk of heart disease. Low levels of selenium have been tied to increased risk of heart disease and higher levels have been shown to reduce risk of heart disease. However, these were observational studies, so more research is needed.

Brain Health: Lower blood levels of selenium have been linked with cognitive decline (including dementia, memory loss, and Alzheimer’s disease). Studies have shown that consuming sufficient levels of antioxidants, such as selenium, from the diet can help reduce risk of developing Alzheimer’s disease as well as improving mental function. The Mediterranean diet, high in selenium-rich foods, is one such dietary source.

Thyroid Health: The thyroid contains more selenium than any other organ and for good reason: it helps protect against oxidative damage and it is important for the production of thyroid hormones. The thyroid regulates metabolism and selenium deficiency is associated with certain thyroid dysfunction, such as hypothyroidism and Hashimoto’s disease. More research is necessary to determine if selenium supplementation could be helpful.

Sources of Selenium

Dietary selenium can be found in plant foods (nuts, whole grains) and in animal sources (seafood, beef, poultry, and dairy). In plant foods, the amount of selenium present varies due to the selenium content of the soil in which they are grown. This can vary widely. For example, one study found that selenium levels in Brazil nuts can vary widely due to their growing region and tree populations. In one region, one nut provided as much as 288% DV of selenium, while others provided 11% DV. Consuming a variety of foods is one way to protect adequate intake. Whole foods are the best way to consume sources of selenium, as this nutrient may be harmed during processing.

Some seafood like oysters, tuna, halibut and sardines are rich in selenium, offering as much as 226% of the recommended daily value.
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Selenium-Rich Foods

• Oysters: 1 cup provides 158 mcg (226% DV)
• Brazil nuts: 1 nut provides 174 mcg (174% DV)
• Halibut: 3 ounces provides 47 mcg (85% DV)
• Tuna: 3 ounces yellowfin tuna provides 544 mcg (989% DV)
• Eggs: 1 large egg provides 16 mcg (23% DV) )
• Sardines: 1 cup provides 79 mcg (112% DV)
• Sunflower seeds: 1 ounce provides 15 mcg (21% DV)
• Chicken breast: 1 cup provides 29 mcg (55% DV)
• Shiitake mushrooms: 1 cup provides 36 mcg (51% DV

Read more on the top selenium-rich foods.

How Much Selenium Do We Need?

Considered a trace mineral, we need just a very small amount of selenium from our diets each day. Because it plays such an active role in our bodily functions, it’s important to consume it regularly. The recommended DV (DV=Daily Value, based on 2,000 calories/day) of selenium increases with age:

Selenium Daily Intake for Children

• 1 to 3 years old- 20 micrograms (mcg)
• 4 to 8 years old- 30 mcg
• 9 to 13 years old- 40 mcg
• 14 to 17 years old- 55 mcg

Selenium Daily Intake for Adults

• 18 years and older- 55 mcg
• Pregnant women- 60 mcg
• Lactating women- 70 mcg

Selenium Supplements

Research from the National Institutes of Health has shown that most people get, on average, more than 100 mcg of selenium from their diets alone each day, so unless you have a condition that puts you at risk for not meeting the daily recommendation, supplementing should not be necessary. Selenium deficiency is rare and it may take years to develop. People with low levels of selenium may use supplements to help prevent or treat complications like muscle disorders, thyroid disorders, heart disease, and immune dysfunction. Other groups who may have low selenium levels may be those with poor dietary intake, those in locations with low levels of selenium in the soil in which their food is grown, and those with chronic diarrhea, Crohn’s disease or other inflammatory bowel disease, people with HIV, and people undergoing kidney dialysis.

Selenium may be used can be found in multivitamins and other dietary supplements, which may contain one of two different forms of the mineral: selenomethionine and sodium selenate. The upper limit for safe selenium dosage per day is 400 mcg for adults. When selenium is sourced from food, this limit is not likely to be met. However, an overdose in a concentrated supplement amount can have negative health outcomes. Symptoms may include bad breath, brittle nails, stomach issues like nausea, fatigue, rashes, and hair loss. In extreme cases, it could lead to more serious issues, like kidney failure, heart failure, and death.

Check with your healthcare provider to determine whether a selenium supplement is right for you, as it may interact with some medications, such as antacids, chemotherapy drugs, statins, and birth control pills. As with any dietary supplement, be sure to purchase them from a reputable source.

The Bottom Line

Deficiency in selenium is rare. Not only do we need just a small amount each day, most of us get all that we need from our diet. As long as most of us eat a healthy variety of foods—aim for plenty of whole foods—there is no need to supplement. If you are concerned that you’re not getting enough selenium, talk with your doctor to see about being tested and the role of supplementing.