Table 1 lists the current RDAs for selenium in mcg. For infants from birth to 12 months, the FNB established an AI for selenium that is equivalent to the mean intake of selenium in healthy, breastfed infants. Brazil nuts, seafoods, and organ meats are the richest food sources of selenium [ 1 ]. Other sources include muscle meats, cereals and other grains, and dairy products. The amount of selenium in drinking water is not nutritionally significant in most geographic regions [ 2 , 6 ]. The major food sources of selenium in the American diet are breads, grains, meat, poultry, fish, and eggs [ 7 ].
The amount of selenium in a given type of plant-based food depends on the amount of selenium in the soil and several other factors, such as soil pH, amount of organic matter in the soil, and whether the selenium is in a form that is amenable to plant uptake [ 2 , 6 , 8 , 9 ].
As a result, selenium concentrations in plant-based foods vary widely by geographic location [ 1 , 2 ]. For example, according to the U. The selenium content of soil affects the amounts of selenium in the plants that animals eat, so the quantities of selenium in animal products also vary [ 2 , 5 ]. However, selenium concentration in soil has a smaller effect on selenium levels in animal products than in plant-based foods because animals maintain predictable tissue concentrations of selenium through homeostatic mechanisms.
Furthermore, formulated livestock feeds generally contain the same levels of selenium. The U. Food and Drug Administration FDA developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet. The DV for selenium is 55 mcg for adults and children aged 4 years and older [ 13 ]. FDA does not require food labels to list selenium content unless selenium has been added to the food.
Few studies have compared the relative absorption and bioavailability of different forms of selenium. Selenium bioavailability, based on urinary excretion, was greatest for selenomethionine and lowest for selenite. However, supplementation with any of these forms only affected plasma selenium levels and not glutathione peroxidase activity or selenoprotein P concentration, confirming that study participants were selenium replete before they began taking selenium supplements.
Most Americans consume adequate amounts of selenium. Adult men have higher daily intakes mcg from foods and mcg from foods and supplements than adult women 93 mcg from foods and mcg from foods and supplements. Men have slightly higher serum selenium levels than women, and whites have higher levels than African Americans [ ]. Selenium intakes and serum concentrations in the United States and Canada vary somewhat by region because of differences in the amounts of selenium in soil and in local foods consumed [ 6 , 20 ].
For example, concentrations are higher in residents of the Midwestern and Western United States than in the South and Northeast [ 19 , 20 ]. The extensive transport of food typically allows people living in low-selenium areas to obtain sufficient amounts of selenium [ 6 ].
Selenium deficiency produces biochemical changes that might predispose people who experience additional stresses to develop certain illnesses [ 6 ]. For example, selenium deficiency in combination with a second stress possibly a viral infection leads to Keshan disease, a cardiomyopathy that occurred in parts of China prior to a government-sponsored selenium supplementation program that began in the s [ 2 , 5 , 8 , 21 ]. Selenium deficiency is also associated with male infertility and might play a role in Kashin-Beck disease, a type of osteoarthritis that occurs in certain low-selenium areas of China, Tibet, and Siberia [ 1 , 2 , 5 , 6 , 8 , 22 ].
Selenium deficiency could exacerbate iodine deficiency, potentially increasing the risk of cretinism in infants [ 2 , 5 ]. Selenium deficiency is very rare in the United States and Canada, and selenium deficiency in isolation rarely causes overt illness [ 6 ].
The following groups are among those most likely to have inadequate intakes of selenium. However, people in some other countries whose diet consists primarily of vegetables grown in low-selenium areas are at risk of deficiency [ 6 ].
The lowest selenium intakes in the world are in certain parts of China, where large proportions of the population have a primarily vegetarian diet and soil selenium levels are very low [ 5 ]. Average selenium intakes are also low in some European countries, especially among populations consuming vegan diets [ 5 , 9 , 23 ].
Although intakes in New Zealand were low in the past, they rose after the country increased its importation of high-selenium wheat [ 9 ].
Selenium levels are significantly lower in patients undergoing long-term hemodialysis than in healthy individuals. Hemodialysis removes some selenium from the blood [ 24 ]. In addition, hemodialysis patients are at risk of low dietary selenium intakes due to anorexia resulting from uremia and dietary restrictions. Although selenium supplementation increases blood levels in hemodialysis patients, more evidence is needed to determine whether supplements have beneficial clinical effects in these individuals.
Selenium levels are often low in people living with HIV, possibly because of inadequate intakes especially in developing countries , excessive losses due to diarrhea, and malabsorption [ 2 , 25 ].
Observational studies have found an association between lower selenium concentrations in people with HIV and an increased risk of cardiomyopathy, death, and, in pregnant women, HIV transmission to offspring and early death of offspring [ ]. Some randomized clinical trials of selenium supplementation in adults with HIV have found that selenium supplementation can reduce the risk of hospitalization and prevent increases of HIV-1 viral load; preventing HIV-1 viral load progression can lead to increases in numbers of CD4 cells, a type of white blood cell that fights infection [ 31 , 32 ].
However, one trial showed that selenium supplementation in pregnant women can prevent early death in infants but has no effects on maternal viral load or CD4 counts [ 33 , 34 ]. This section focuses on four diseases and disorders in which selenium might play a role: cancer, cardiovascular disease, cognitive decline, and thyroid disease.
Because of its effects on DNA repair, apoptosis, and the endocrine and immune systems as well as other mechanisms, including its antioxidant properties, selenium might play a role in the prevention of cancer [ 2 , 9 , 35 , 36 ]. Epidemiological studies have suggested an inverse association between selenium status and the risk of colorectal, prostate, lung, bladder, skin, esophageal, and gastric cancers [ 37 ].
The authors found no association between selenium intake and risk of breast cancer. A meta-analysis of 20 epidemiologic studies showed a potential inverse association between toenail, serum, and plasma selenium levels and prostate cancer risk [ 38 ]. Randomized controlled trials of selenium supplementation for cancer prevention have yielded conflicting results.
The authors of a Cochrane review concluded, based on nine randomized clinical trials, that selenium might help prevent gastrointestinal cancers but noted that these results need to be confirmed in more appropriately designed randomized clinical trials [ 39 ]. A secondary analysis of the double-blind, randomized, controlled Nutritional Prevention of Cancer Trial in 1, U.
An additional 1. In , the FDA allowed a qualified health claim on foods and dietary supplements containing selenium to state that while "some scientific evidence suggests that consumption of selenium may reduce the risk of certain forms of cancer FDA has determined that this evidence is limited and not conclusive" [ 43 ]. More research is needed to confirm the relationship between selenium concentrations and cancer risk and to determine whether selenium supplements can help prevent any form of cancer.
Selenoproteins help prevent the oxidative modification of lipids, reducing inflammation and preventing platelets from aggregating [ 9 ]. For these reasons, experts have suggested that selenium supplements could reduce the risk of cardiovascular disease or deaths associated with cardiovascular disease. The epidemiological data on the role of selenium in cardiovascular disease have yielded conflicting conclusions. Some observational studies have found an inverse association between serum selenium concentrations and risk of hypertension or coronary heart disease.
A meta-analysis of 25 observational studies found that people with lower selenium concentrations had a higher risk of coronary heart disease [ 44 ]. However, other observational studies failed to find statistically significant links between selenium concentrations and risk of heart disease or cardiac death, or they found that higher selenium concentrations are associated with an increased risk of cardiovascular disease [ ].
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Mayo Clinic does not endorse companies or products. It might also cause Kashin-Beck disease, a type of arthritis that produces pain, swelling, and loss of motion in your joints. Scientists are studying selenium to understand how it affects health. Here are some examples of what this research has shown. Studies suggest that people who consume lower amounts of selenium could have an increased risk of developing cancers of the colon and rectum, prostate, lung, bladder, skin, esophagus, and stomach.
But whether selenium supplements reduce cancer risk is not clear. More research is needed to understand the effects of selenium from food and dietary supplements on cancer risk. Scientists are studying whether selenium helps reduce the risk of cardiovascular disease.
Some studies show that people with lower blood levels of selenium have a higher risk of heart disease, but other studies do not. More studies are needed to better understand how selenium in food and dietary supplements affects heart health. Blood selenium levels decrease as people age, and scientists are studying whether low selenium levels contribute to a decline in brain function in the elderly.
Some studies suggest that people with lower blood selenium levels are more likely to have poorer mental function. But a study of elderly people in the United States found no link between selenium levels and memory. More research is needed to find out whether selenium dietary supplements might help reduce the risk of or treat cognitive decline in elderly people. The thyroid gland has high amounts of selenium that play an important role in thyroid function. Studies suggest that people—especially women—who have low blood levels of selenium and iodine might develop problems with their thyroid.
But whether selenium dietary supplements can help treat or reduce the risk of thyroid disease is not clear. More research is needed to understand the effects of selenium on thyroid disease. A systematic review and meta-analysis of nine controlled trials did not find that selenium supplements changed thyroid hormone function in people with ATD, nor did a Cochrane review. Selenoproteins help to protect cell membranes from damage by free radicals and keep blood platelets from becoming sticky, both of which can lead to heart disease.
However, both cohort studies and clinical trials have shown mixed results regarding the relationship of selenium and cardiovascular disease CVD. Observational studies have shown that people with both low and high selenium exposure based on dietary intake and blood levels have an increased risk of CVD. Others have found no association at all. Additional research is needed on the association of selenium and CVD before making specific dietary recommendations.
The amount of selenium in foods can vary widely depending on the selenium content of the soil in which it is grown. Soil content varies widely by region. Plant foods obtain selenium from soil, which will then affect the amount of selenium in animals eating those plants.
Protein foods from animals are generally good sources of selenium. Seafood, organ meats, and Brazil nuts are the foods highest in selenium although Americans obtain most of their selenium from everyday staples, like breads, cereals, poultry, red meat, and eggs. A deficiency of selenium in the U. Two conditions are associated with severe selenium deficiency: 1 Keshan disease, a type of cardiomyopathy, or disease of heart muscle, and 2 Kashin-Beck disease, a form of osteoarthritis.
Chronically high intakes of selenium can lead to health problems, ranging from muscle tremors, hair loss, stomach upset, and lightheadedness, to more severe outcomes of heart attack, respiratory distress, or kidney failure.
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