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Selenium

Written by Ada’s Medical Knowledge Team

Updated on

Selenium is a trace element which plays a role in lots of processes in the body, including metabolism and preventing damage caused by infection and inflammation.[1] Selenium deficiency is rare. Most people should be able to get enough selenium from their diet.

Foods with selenium include brazil nuts, meat, fish, and eggs.[2] Taking a low dose of selenium supplements is unlikely to cause harm. You can read more about selenium and its sources in the following article.

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What is selenium?

Selenium is a trace element which supports overall health. Selenium benefits the immune system and plays an important role in metabolism, reproduction, thyroid gland function, and DNA production. It also prevents damage to body cells and tissues caused by infection and inflammation.[2][3]

What is selenium good for?

Higher dietary selenium intake is associated with lower cholesterol levels and lower risks of developing colorectal, prostate, lung, bladder, skin, esophageal, and stomach cancers.[1] Some studies show blood selenium levels are lower in people with type 1 diabetes.

There is some evidence to suggest there may be a role for selenium supplements in lowering blood sugar levels.[3] Selenium, in the form of selenium sulfide, can be applied to the skin and scalp to treat dandruff and fungal infections.[4]

What foods have selenium?

Selenium is present in the soil and is taken up by plants. The selenium is then transferred to humans and animals when they eat plants. Foods with selenium include brazil nuts, fish, meat, and eggs.[2][1]

Brazil nuts (1 nut): 68-91 Micrograms (mcg) Sardines, canned in oil, 3 ounces: 45 Micrograms (mcg) Beef steak, roasted, 3 ounces: 33 Micrograms (mcg) Cottage cheese, 1 cup: 20 Micrograms (mcg) Egg, hard boiled, 1 large: 15 Micrograms (mcg) Oatmeal, unenriched, 1 cup: 13 Micrograms (mcg) Baked beans, 1 cup: 13 Micrograms (mcg)

Who should take selenium supplements?

If you eat a balanced diet containing meat, fish and nuts, you should be able to get enough selenium from your diet.[2] Selenium levels are generally lower in people who follow a vegan diet. Brazil nuts are one of the highest selenium-containing foods.

The amount of selenium you need every day depends on your age, and whether you are pregnant or breastfeeding.[1]

  • Infants (birth to 12 months): 15-20 micrograms (mcg)/day
  • Children/adolescents (1 to 18 years): 20-55mcg/day
  • Adults: 55 mcg/day (increased to 60 mcg during pregnancy and 70 mcg during breastfeeding).

Taking up to 350 micrograms of selenium supplements is unlikely to cause harm.[2]

People undergoing kidney dialysis or living with HIV might have lower selenium levels. Kidney dialysis removes some selenium from the blood.

More research and evidence is needed to decide whether selenium supplements have benefits for people on dialysis. Selenium is also lower in people living with HIV. Some studies show that selenium supplementation could benefit people living with HIV.[1]

You should speak to your doctor before taking selenium supplements, as they can interact with some medications.[1]

What are side effects of selenium?

Taking too much selenium can be harmful.[3]. Brazil nuts contain very high amounts of selenium. 1 brazil nut can contain twice the recommended daily amount of selenium. It is possible to consume too much selenium through regularly eating lots of brazil nuts. It is also important to check the dose of selenium supplements and to speak to a doctor before taking them.

The symptoms of excess selenium are:

  • Hair loss
  • Brittle nails
  • Metallic taste in the mouth
  • Garlic breath odor
  • Feeling sick
  • Diarrhoea
  • Irritability
  • Fatigue
  • Muscle weakness
  • Difficulty breathing [1][3]

When is a selenium test useful?

A selenium test is useful if you think you might not be getting enough selenium from your diet. This means if you don’t eat a varied, balanced diet that contains meat, or fish or eggs or nuts.

Selenium deficiency is very rare. It can cause male infertility and cardiomyopathy, a disease of the heart muscle. It can also cause Kashin-Beck disease, a type of arthritis causing pain and swelling of the joints.[5]

If you think you might have selenium deficiency or develop the symptoms of selenium deficiency, you should speak to a doctor. Symptoms of selenium deficiency are:[5]

  • Joint pain
  • Swollen joints
  • Muscle pain
  • Muscle weakness
  • Low mood
  • Infertility
  • Weakened immune system
  • Irregular heartbeat
  • Breathlessness

Selenium FAQ

Q: What does selenium do? A: Selenium is essential for the healthy function of the immune system, metabolism and reproduction. It helps to prevent damage to body cells and tissues caused by infection and inflammation.

Q: How much selenium do I need? A: The required daily amount of selenium depends on your age, and whether you are pregnant or breastfeeding.

  • Infants (birth to 12 months): 15-20 micrograms (mcg)/day
  • Children/adolescents ( 1 to 18 years): 20-55mcg/day
  • Adults: 55 mcg/day (increased to 60 mcg during pregnancy and 70 mcg during breastfeeding).

Q: Why is selenium important? A: Selenium plays an important role in lots of bodily processes, including body metabolism and preventing body cell damage from infection and inflammation. Selenium deficiency is rare. It is associated with male infertility, heart muscle disease, a rare joint disease called Kashin-Beck disease.[5] Most people get enough selenium through their diet.

Q: What is selenium testing? A: A selenium test measures the amount of selenium in the blood. This involves a small sample of blood being taken from a vein in your arm.

Q: When do I need to seek medical help? A: Speak to your doctor if you are thinking of taking selenium supplements. They can interact with some medications. If you develop the symptoms of selenium toxicity including nausea, diarrhoea, irritability and fatigue, you should speak to a doctor. You can see the section ‘what are the side effects of selenium’ for more information.


  1. National Institutes of Health (2021). Selenium: Fact Sheet for Health Professionals. Accessed 27th April, 2022.

  2. NHS (2020). Vitamins and minerals. Accessed April 22nd April, 2022.

  3. Wang N et al. (2017).Supplementation of Micronutrient Selenium in Metabolic Diseases: Its Role as an Antioxidant.. Accessed April 27th, 2022.

  4. Electronic medicines compendium (2021). Selsun Shampoo 2.5%. Accessed 27th April, 2022.

  5. National library of Medicine (2021).Selenium Deficiency. Accessed 27th April, 2022.

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