Selenium: symptoms of deficiency and overdose

Selenium is a  mineral that performs numerous important functions. Selenium has a similar function to vitamin E in the human body, as it protects cells from damage caused by free radicals. For this reason, selenium is also popular as a dietary supplement. However, it can also be ingested through food. What exactly is the effect of selenium in the body, what are the symptoms of a deficiency or an overdose and which foods contain selenium?

What is selenium?

Selenium belongs to the group of minerals and is counted among the essential trace elements. It was named after the Greek moon goddess Selene because of its silvery-grey luster and was discovered in 1817 by the Swedish chemist Jöns Jakob Berzelius. It was only discovered in 1975 that it also occurs in the human body.

The amount of selenium in the body is around 10 to 15 milligrams. A large part of it is contained in the muscles, but it is also mainly in the liver, kidneys and heart. Selenium is absorbed in the upper parts of the small intestine and excreted primarily through the urine.

Health effects of selenium

Selenium is a component of important enzymes and helps (in the form of the enzyme glutathione peroxidase) the body’s cells to defend against aggressive metabolic products, the so-called free radicals. In this function, like vitamins A, C and E, it is one of the so-called antioxidants. The free oxygen radicals are formed in almost all metabolic processes and, if they are present in excess, can damage the body cells and the genetic material (DNA) they contain.

In addition, selenium has an influence on fertility in men, since certain components of sperm production depend on it. In addition, selenium also protects the body from toxic heavy metal compounds (cadmium, lead, arsenic, mercury) by binding these substances.

Some enzymes that control the production of hormones in the thyroid also depend on the mineral for their function. The use of selenium supplements in inflammatory diseases of the thyroid gland ( Hashimoto’s thyroiditisGraves ‘ disease) is therefore often discussed . The selenium should then improve the general condition and some of the symptoms. So far, however, there is no scientific evidence for this assumption.

Does selenium protect against cancer?

In the 1960s, some studies came to the conclusion that an increased selenium intake through food could possibly protect against cancer. However, these were purely observational studies in areas with a selenium-rich diet, which means that the researchers did not specifically control the study conditions. Other factors, such as the lifestyle of the study participants or other diets, were not evaluated. The informative value of such studies is therefore very limited.

A current, comprehensive analysis of various studies with a total of 27,000 participants on the potential cancer-preventive effect of the mineral now shows very clearly: There is no evidence that the increased intake of selenium can protect against cancer.

defenses and immune system

Selenium has a positive effect on the  immune system .  In the form of dietary supplements, it is often offered commercially in combination with  zinc to strengthen the immune system.

An optimally adjusted selenium level should also have a positive effect on the health of those affected with  HIV , allergic  asthma  or rheumatic diseases.

Daily requirement of selenium

Based on estimates, the German Society for Nutrition recommends a daily selenium intake of  60 micrograms  for women over the age of 15 and  70 micrograms for men over the age of 15  – the recommendations of the World Health Organization (WHO) are slightly lower at 55 micrograms.

In pregnant women, the daily requirement is only minimally increased. Breastfeeding women, on the other hand, should consume around 75 micrograms of selenium per day.

Selenium deficiency: Soils in Germany are low in selenium

In many regions of Europe, including Germany, the soil contains little selenium – partly due to the after-effects of acid rain contaminated with sulfur dioxide and sulphurous fertilizers. Sulfur is then taken up by the plants instead of selenium   .

Due to the large differences in the selenium content of the soil, the selenium content in crops also varies greatly. Animal proteins are therefore usually better sources of selenium than vegetable foods in selenium-poor cultivation areas. Because the trace element is often added to animal feed – also because it makes the animals less susceptible to disease.

Some researchers classify Germany as a selenium deficiency area, because the actual selenium intake often falls short of the recommendation of the German Society for Nutrition.

A selenium deficiency is determined via the blood serum. In adults, less than 50 micrograms per liter is considered to have a suboptimal selenium status. If there is a selenium deficiency, dietary supplements can be used to compensate.

Causes and those affected by a selenium deficiency

A selenium deficiency can occur for various reasons:

  • In many cases, people are affected by a selenium deficiency who, on the one hand, take in little selenium with their food: These include people who eat a too one-sided  vegan  diet, people with an overall one-sided or deficient diet, people fed with tube feeding and dialysis patients. Alcohol abuse can also lead to selenium deficiency.
  • A selenium deficiency can also occur if the trace element is increasingly excreted: This can happen in the case of long-lasting diarrhea, but also via the urine in the case of  diabetes  mellitus or severe kidney diseases.
  • Gastrointestinal diseases (e.g. chronic inflammatory bowel diseases such as  ulcerative colitis ) can lead to impaired selenium absorption.
  • An increased need for selenium can occur during pregnancy, heavy menstrual bleeding and breastfeeding. The body also “consumes” more selenium in the case of cancer.

Selenium deficiency: symptoms

The consequences of a selenium deficiency have not yet been definitively researched. In areas of extreme selenium deficiency in China and Central Africa, the most severe diseases of the heart muscle and joints have been observed. However, it is still unclear whether this so-called Keshan disease and Kashin-Beck disease are actually the result of a selenium deficiency or whether other triggers are present.

Recent studies also suggest a connection between low selenium levels and  high blood pressure , dyslipidemia and the development of  arteriosclerosis  . There is also evidence that a selenium deficiency can impair fertility: women who suffered miscarriages had extremely low blood levels of the trace element. In men with a selenium deficiency, the maturation and motility of the sperm can be disturbed. In addition, the immune system and muscle function can be impaired.

Symptoms of a selenium overdose

Selenium has toxic effects in higher concentrations. Normally, therefore, the body excretes excess selenium with the urine. However, if large amounts are regularly consumed over a longer period of time, for example through the unnecessary or excessive intake of food supplements, symptoms can arise.

Possible consequences are fatigue,  nauseadiarrhea , joint pain and nerve disorders. In the further course of this selenium poisoning, the so-called selenosis, hair loss, loss of nails, liver damage, heart muscle weakness and a typical smell of  garlic on the breath  can occur. Memory disorders and problems with the eyes in the form of blurred vision can also occur with an overdose. Acute selenium poisoning can be fatal.

According to the recommendations of the European Food Safety Authority (EFSA), adults should therefore  not exceed a daily intake of 300 micrograms of  selenium  .  For children, depending on age and body weight, the reference value for a maximum daily intake is 60 to 250 micrograms. Dietary supplements containing selenium should only be taken if a selenium deficiency has been diagnosed and should never be taken without consulting a doctor.

Content of selenium in food

The following is an example of the  selenium content  of some foods  per 100 grams  :

  • Brazil nuts: 103 micrograms
  • Mackerel: 39 micrograms
  • Mushrooms: 7 micrograms
  • Rye bread: 3 micrograms
  • Yogurt : 1.5 micrograms
  • dried lentils: 9.9 micrograms

Animal and vegetable proteins are good sources of selenium. Examples of foods that are particularly rich in selenium are offal, meat and fish, cereals,  nuts  (especially Brazil nuts) and legumes, as well as porcini mushrooms.

When buying, give preference to products from organic farming – since they do not use sulphurous fertilizers, they contain more selenium.

In addition, it is advisable to consume food with a high content of vitamins A, C and E, as these improve the bioavailability of selenium in the body.

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