Selenium: an essential mineral for immune function and the nervous system

Selenium: an essential mineral for immune function and the nervous system

Written by

Anna Roell
18 July, 2023

Medically checked article All HOMED-IQ content is reviewed by medical specialists

Selenium is an essential trace element that is important for many processes in our body, including supporting the immune system and protecting against oxidative stress. But what happens when our body does not have a sufficient supply of selenium? And which foods contain selenium? In this article we go into the importance of selenium and explain what happens when our body has either too little or too much of it.

What is selenium?

Selen is an essential trace element, which means it is a mineral that our body needs in very small quantities, but is nevertheless essential for its proper functioning. We cannot produce it ourselves and must therefore take it in through our diet (Harvard Health, 2023). 

What is the function of selenium in the body?

Selenium plays a critical role in many processes in the body. These factors can include:

  1. Antioxidant effect: Selenium is an important component of the enzymes that neutralise free radicals. Free radicals can damage cells when they accumulate in the body. This condition is called oxidative stress. By neutralising the free radicals, selenium helps to reduce oxidative stress and prevent cell damage.
  2. Thyroid function: Selenium also plays an important role in the thyroid gland. The thyroid gland plays an important role in regulating metabolism and body temperature. It does this by producing thyroid hormones, especially triiodothyronine (T3) and thyroxine (T4). Selenium is an integral component of several enzymes that are important for converting the inactive thyroid hormone T4 into the active thyroid hormone T3, thus enabling the hormones to function. 
  3. Immune system: Selenium also supports the function of the immune system. It is involved in the production and function of immune cells and is associated with an enhanced immune response. Conversely, selenium deficiency is associated with a slower immune response.
  4. Nervous system: Selenium plays an important role in various aspects of brain function and nervous system health. Some specific selenium-containing proteins, called selenoproteins, have various functions, including regulating inflammatory responses in the brain and supporting brain development.

Source: Rayman, 2012

How much selenium should one take daily?

Adults over 19 years of age are recommended to consume 55 micrograms of selenium per day. Pregnant women should consume 60 micrograms, while breastfeeding women should consume 70 micrograms per day.

However, it is important to note that selenium requirements can depend on many factors, including overall health and individual metabolism. If you have questions about your specific selenium needs, consult your doctor (NIH, 2021).

What foods contain selenium?

Most people obtain enough selenium through their diet, and a variety of foods can serve as a source of selenium. It should be noted that the selenium content in plants and animals is highly dependent on the amount of selenium in the soil on which they are grown or fed. Examples of foods high in selenium include:

  • Fish and seafood: Fish and seafood are excellent sources of selenium. Tuna, salmon, cod, shrimp and oysters are among the best sources of this important mineral.
  • Meat and poultry: Animal products such as beef, chicken, turkey and pork also contain considerable amounts of selenium. However, the exact amount can vary depending on the type of animal, its diet, and its living conditions.
  • Eier: Eggs are another good source of selenium, especially the yolk.
  • Whole grain products: Whole grain bread, brown rice and oatmeal also contain selenium. Again, the amount may vary depending on the soil in which they are grown.
  • Nuts and seeds: Brazil nuts in particular are known for their high selenium content. A single Brazil nut contains about 68-91 mcg, so that one or two nuts already cover your daily selenium requirement. But sunflower seeds and linseeds also contain selenium.
  • Legumes: Beans, lentils and chickpeas are also sources of selenium.

Source: Cleveland Clinic, 2023

What is a selenium deficiency?

A selenium deficiency occurs when the body does not get enough selenium to function properly. This can lead to a number of health problems, including weakening of the immune system, cardiovascular disease, and problems with the thyroid gland (Kieliszek & Błażejak, 2013).

Who is at increased risk for selenium deficiency?

Selenium deficiency is relatively rare in most parts of the world, but can occur in certain populations that are at increased risk. Examples of foods high in selenium include:

  • People with autoimmune diseases: Some autoimmune diseases can interfere with the absorption of selenium from the diet or lead to an increased need for this mineral. In people with celiac disease, the ingestion of gluten damages the intestinal lining and can impair the absorption of nutrients, which might reduce an individual’s ability to absorb adequate selenium. Crohn’s disease, an autoimmune condition that causes chronic inflammation of the digestive tract, may also cause impaired absorption of nutrients including selenium.
  • People with other diseases: Selenium levels are significantly lower in people undergoing kidney dialysis as a result of certain kidney diseases than in healthy people. Haemodialysis removes some of the selenium from the blood. Selenium levels are also often low in HIV-infected people, possibly due to inadequate intake, excessive losses through diarrhoea and malabsorption.
  • People living in selenium-deficient regions: Selenium levels in foods can vary widely, depending on the selenium content of the soil in which plants are grown or animals are fed. In some parts of the world, such as certain regions of China and Europe, selenium levels in the soil are low, which may mean that people living in these regions do not get enough selenium through their diets.

Source: NIH, 2021

What symptoms indicate a selenium deficiency?

Symptoms of selenium deficiency can vary in severity and are often nonspecific, making them difficult to diagnose. Common symptoms include:

If the deficiency is severe or persistent, more specific symptoms may occur, such as Keshan disease (a specific heart disease) or Kashin-Beck disease (a type of arthritis).

It is important to note that many of these symptoms can also occur with other diseases or nutrient deficiencies. Therefore, it is difficult to diagnose a selenium deficiency based on symptoms alone. If you suspect you may have a selenium deficiency, consult a doctor for follow-up testing.

Quelle: Olsen, 2023

What other diseases is selenium associated with?

In addition to its importance in the immune system and thyroid function, the role of selenium in the prevention and treatment of various diseases is being studied. Some research suggests that low levels of selenium in the blood may be associated with an increased risk of cardiovascular disease. Because blood selenium concentrations decline with age, low or deficient selenium concentrations may be associated with age-related declines in brain function. While further research in this area is needed, getting adequate selenium is a good idea in supporting your overall health (NIH, 2021).

What happens in the event of a selenium overdose?

Elevated selenium levels, known as selenosis, can be caused by excessive intake of selenium, often through consuming too many supplements or brazil nuts, which contain large amounts of selenium. Symptoms can vary depending on the severity of selenosis, but may include:

  • Nausea, vomiting and diarrhea
  • Hair loss, nail changes, skin rashes
  • Gum inflammation
  • Irritability
  • Fatigue
  • Nerve damage (neuropathy)

Serious health consequences can occur if selenium levels remain high for a long period of time, including severe neurological and gastrointestinal problems, heart problems, and even death in extreme cases. It is important to seek immediate medical attention if selenosis is suspected.

In order to prevent selenosis, supplements containing selenium should be taken with caution and under the guidance of a healthcare provider (Kieliszek & Błażejak, 2013; Harvard Health, 2023). It is also important to only consume foods that are high in selenium in moderation, such as brazil nuts.

How is a selenium deficiency or overdose diagnosed?

Diagnosis of high or low selenium levels is usually based on a combination of symptoms and laboratory tests. Symptoms alone are often non-specific and can indicate a variety of health conditions, so blood tests are crucial. If a selenium deficiency or selenium poisoning is suspected, a doctor may order a blood test to measure the level of selenium in the blood. It should be noted that these tests are not always conclusive, as blood selenium levels can also be affected by factors such as recent consumption of selenium-rich foods. Hair or nail samples can also be taken to assess selenium status over time (Olsen, 2023).

Would you like to check in on your own health from home?

Nutritional deficiencies often cause non-specific symptoms, making it difficult to identify the root cause. Homed-IQ’s blood tests can provide insight into your nutritional status from the comfort of home. As selenium is essential for the synthesis of thyroid hormones, Homed-IQ’s Thyroid Test can be used to assess thyroid function without visiting a doctor’s office. If you would like to test the level of other essential vitamins in your body, Homed-IQ’s Vitamin Deficiency Test can provide valuable insight into your overall nutritional status. With laboratory-certified test results from a simple finger prick, Homed-IQ’s home tests make it possible to proactively take care of one’s health and take action when needed.

What are the treatment options for a selenium deficiency or overdose?

In the case of selenium deficiency, a doctor may recommend making changes to your diet to include more selenium rich foods. In the case of a severe deficiency or if the person has difficulty getting enough selenium through their diet, a doctor may prescribe selenium supplements. If the cause of selenium deficiency is due to another medical condition, the underlying cause may need to be treated first.

In cases of selenium poisoning (selenosis), the primary treatment is to immediately reduce or stop the intake of selenium. In severe cases, medical detoxification may be necessary.


Selenium is a vital nutrient that is essential for the immune system, thyroid function, and nervous system health. A deficiency can cause various symptoms, including fatigue, a weakened immune system, and cognitive problems. At the same time, excessive intake of selenium can lead to health problems known as selenosis. It is important to maintain adequate selenium levels through a balanced diet to promote health and well-being.


Benefits of Selenium. (2023, May 31). Cleveland Clinic Health Essentials. Retrieved July 6, 2023, from

Kieliszek, M., & Blazejak, S. (2016). Current Knowledge on the Importance of Selenium in Food for Living Organisms: A Review. Molecules, 21(5), 609.

O’Carroll, D. (n.d.). Selenium Deficiency: Symptoms, Causes, and Treatment. Healthline. Retrieved July 6, 2023, from

Rayman, M. P. (2012). Selenium and human health. The Lancet, 379(9822), 1256-1268.

Selenium – Health Professional Fact Sheet. (2021, March 26). NIH Office of Dietary Supplements. Retrieved July 6, 2023, from

Selenium | The Nutrition Source | Harvard T.H. Chan School of Public Health. (n.d.). Harvard T.H. Chan School of Public Health. Retrieved July 6, 2023, from

About the author

Anna Roell

Anna is a trained nurse and health economist specializing in epidemiology, combining her medical and scientific interests. Her goal is to improve others' understanding of medical information and to communicate it in an understandable way. Anna is originally from Germany and now lives in Amsterdam. What she appreciates most about Amsterdam is the open-minded, active attitude of the people, the markets, and the beautiful nature in the areas surrounding Amsterdam.