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What is selenium and what does it do?

Selenium is a nutrient that the body needs to stay healthy. Selenium is important for reproduction, thyroid gland function, DNA production, and protecting the body from damage caused by free radicals and from infection.

Selenium is a trace element that is naturally present in many foods, added to others, and available as a dietary supplement. Selenium, which is nutritionally essential for humans, is a constituent of more than two dozen selenoproteins that play critical roles in reproduction, thyroid hormone metabolism, DNA synthesis, and protection from oxidative damage and infection [1].

Selenium exists in two forms: inorganic (selenate and selenite) and organic (selenomethionine and selenocysteine) [2]. Both forms can be good dietary sources of selenium [3]. Soils contain inorganic selenites and selenates that plants accumulate and convert to organic forms, mostly selenocysteine and selenomethionine and their methylated derivatives.

Most selenium is in the form of selenomethionine in animal and human tissues, where it can be incorporated nonspecifically with the amino acid methionine in body proteins. Skeletal muscle is the major site of selenium storage, accounting for approximately 28% to 46% of the total selenium pool [3]. Both selenocysteine and selenite are reduced to generate hydrogen selenide, which in turn is converted to selenophosphate for selenoprotein biosynthesis [4].

How much selenium do I need?

The amount of selenium that you need each day depends on your age. Average daily recommended amounts are listed below in micrograms (mcg).



  Birth to 6 months

15 mcg  

  Infants 7–12 months

20 mcg  

  Children 1–3 years

20 mcg  

  Children 4–8 years

30 mcg  

  Children 9–13 years

40 mcg  

  Teens 14–18 years

55 mcg  

  Adults 19–50 years

55 mcg  

  Adults 51–70 years

55 mcg  

  Adults 71 years and older

55 mcg  

  Pregnant teens and women

60 mcg  

  Breastfeeding teens and women

70 mcg  

What happens if I don’t get enough selenium?

Selenium deficiency is very rare in the United States and Canada. Selenium deficiency can cause Keshan disease (a type of heart disease) and male infertility. It might also cause Kashin-Beck disease, a type of arthritis that produces pain, swelling, and loss of motion in your joints.

What are some effects of selenium on health?

Scientists are studying potassium 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.

Cardiovascular disease

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.

Cognitive decline

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.

Thyroid disease

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.

Can selenium be harmful?

Yes, if you get too much. Brazil nuts, for example, contain very high amounts of selenium (68–91 mcg per nut) and can cause you to go over the upper limit if you eat too many. Getting too much selenium over time can cause the following:
  • Garlic breath
  • Nausea
  • Diarrhea
  • Skin rashes
  • Irritability
  • Metallic taste in the mouth
  • Brittle hair or nails
  • Loss of hair or nails
  • Discolored teeth
  • Nervous system problems

Extremely high intakes of selenium can cause severe problems, including difficulty breathing, tremors, kidney failure, heart attacks, and heart failure.
The daily upper limits for selenium include intakes from all sources—food, beverages, and supplements—and are listed below.



  Birth to 6 months

45 mcg  

  Infants 7–12 months

60 mcg  

  Children 1–3 years

90 mcg  

  Children 4–8 years

150 mcg  

  Children 9–13 years

280 mcg  

  Teens 14–18 years

400 mcg  


400 mcg  

Where can I find out more about selenium?

• For general information on selenium:
Office of Dietary Supplements Health Professional Fact Sheet on Selenium
o Selenium in Diet , MedlinePlus®
• For more information on food sources of selenium:
o U.S. Department of Agriculture’s (USDA) FoodData Central 
o Nutrient List for selenium (listed by food or by selenium content), USDA
• For more advice on choosing dietary supplements:
• For information about building a healthy dietary pattern:


1. Sunde RA. Selenium. In: Ross AC, Caballero B, Cousins RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease. 11th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2012:225-37

2. Sunde RA. Selenium. In: Bowman B, Russell R, eds. Present Knowledge in Nutrition. 9th ed. Washington, DC: International Life Sciences Institute; 2006:480-97

3. Terry EN, Diamond AM. Selenium. In: Erdman JW, Macdonald IA, Zeisel SH, eds. Present Knowledge in Nutrition. 10th ed. Washington, DC: Wiley-Blackwell; 2012:568-87

4. Davis CD. Selenium supplementation and cancer prevention. Curr Nutr Rep 2012;1:16-23.

5. Health information data from U.S. National Institutes of Health

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