Selenium occurs only in traces in the human body. An adult weighing 70 kg has just about 7 milligrams on average. In medicine, selenium is considered a vital, essential trace element. It plays an important role in detoxifying the body, protects the membrane of our body cells, prevents red blood cells from oxidizing and is part of some important enzymes.
Selenium belongs to the semi-metals. It stands at the 59th place in the frequency of the elements in the Earth’s surface. It rarely occurs in nature in its pure form. We usually find it in compounds with sulfur. Selenium minerals are also rare. Clausthalite and naumannite are known examples. Selenides are found in copper gravel and zinc blend. Selenium is used in the semiconductor industry for the production of photodiodes, photocells, radar systems, solar cells and light meters. It is used in photocopiers because of its photoelectric property. Tiny additions to glass give it a bright red color. In the red traffic lights, we experience this color in daily life.
The vital necessity of selenium for plants, humans and animals was only discovered in 1957. With selenium deficiency, young animals do not gain weight properly. In humans occur very specific deficiency diseases.
Functions in the body
Selenium fulfills its most important function as a component of the enzyme glutathione peroxidase. This important enzyme is mainly found in red blood cells. It protects them from attack by harmful oxygen radicals that are produced in normal metabolic processes, but also by smoking, alcohol, ozone, smog and ionizing radiation.
Together with vitamin E, the enzyme also protects all cell membranes. Various fats are built into the membrane, which are wafer-thin boundary layers, that must be particularly protected. If such biological membranes are destroyed, premature cell death or genetic damage to the DNA occurs.
However, the body uses this selenium-containing enzyme very sparingly. If it is consumed, it is regenerated by vitamins C and E. Vitamin B2, carotenoids and anthocyanins also play an important role in this metabolic process. So we see the importance of a diet rich in vitamin-packed unprocessed plants.
Selenium is also contained in another enzyme, iodinethyronine-5-deiodase. Here it controls the conversion of the thyroid hormone thyroxine into the biologically active form. It therefore has an influence on the basal metabolic rate, cell differentiation, cell growth and the rate of cell division.
Selenium also plays a role in the detoxification of heavy metals. It binds cadmium, lead and mercury, so that these toxic metals can no longer bind to vital proteins.
Selenium also stimulates the immune system. Research in recent years also suggests that selenium plays an important role in cancer prevention. In cancer patients, a much lower selenium levels are found in the blood.
Some soils are very low in selenium. This affects Central and Northern Europe but also large parts of China. An increased incidence of the so-called Keshan’s disease has also been found there. In its chronic form, this disease manifests itself as cardiac insufficiency with simultaneous enlargement of the heart muscle. In the area where this disease has occurred more frequently, the salt has been enriched with selenium and has thus been able to be suppressed.
The first symptoms of selenium deficiency include myopathies, which are muscle weaknesses. Metabolic disorders of the liver and pancreas are often associated with a selenium deficiency. Low levels of selenium in tissues have also been found in various forms of arthritis and degenerative joint diseases.
It is interested to notice that in those areas of China where the soil is selenium deficient, mortality of COVID-19 was much higher than in other parts o the country. That stresses again the importance of Selenium for the immune system.
Chemotherapy of cancer as well as oxygen therapies lead to increased formation of free radicals, which can be intercepted by selenium and other antioxidants.
Animal foods generally contain higher amounts of selenium than plant foods. But selenium from the plant is more bioavailable, so it is more easily absorbed by the body. High amounts of vitamin C, being still in the physiological range, improve the absorption from the gastrointestinal tract.
Nuts and seeds have high amounts of selenium. The Brazil nut has by far the highest selenium content, even multiple times more than animal products. Chia and sunflower seeds have moderate amounts of selenium, Soybeans and white beans are also good sources. Substantial amounts are also found in whole grain, millet and rice, but this depends on the selenium content of the soil. Finland is a very selenium-poor area. The soils there are enriched with selenium. Other countries in Central and Northern Europe are also discussing enrichment.
Those who live in areas with selenium-poor soils should not eat exclusively products from their own garden or the farmers from the surrounding area. Supplementing your diet with some nuts and seeds grown in tropical areas can help to balance this deficiency. Brazil nuts tend to be especially high in selenium, but can vary greatly depending on soil conditions. Eating just two Brazil nuts normally gives you more than your daily need. Since Brazil Nuts are so high in selenium, you should be cautious to not overuse them, though eating up to 4 nuts daily on a regular basis you should be still in the safe zone.
Overdosage and Poisoning
Before it was discovered that selenium is vital for humans, the trace element was considered one of the most toxic elements. However, acute selenium poisoning has occurred very rarely. In the production of glass and paints and in electronics, where selenium is used, however, protection of employees is necessary.
An overdosage is highly unlikely via food alone. However, supplementation with selenium is increasingly popular. Corresponding preparations are already on the shelves of supermarkets and drugstores. Whether a general supplementation can be recommended is controversial because the knowledge about the trace element is still insufficient. Therefore, an independent intake of selenium-containing supplements should be discouraged. They belong in the hands of an experienced doctor. It is certain that the additional intake of selenium is recommended for cancer, special forms of arthritis and certain cardiovascular diseases. However, the amounts to be taken vary depending on the respective course of treatment. This again shows that only the attending physician should decide on selenium supplementation.
To avoid a selenium deficiency, a balanced diet is key. Problems are only likely to arise in areas with selenium-poor soils and limited food choices at the same time. With the exception of the Brazil nut, plant products have lower selenium levels, but this is made up by better absorption and better recycling of selenium containing enzymes. Once again it has been shown that a varied diet with a high proportion of plant-based food is the right way to go.
Esther Neumann studied Nutrition at the University of Vienna. Since then she served as an author for the health magazine “Leben und Gesundheit” and conducted health lectures in various locations of Austria.