Selenium - Benefits And Functions
Selenium is an essential mineral that belongs to the group of trace elements. The name selenium is derived from the Greek word Selene, which means moon. This trace element must be consumed daily through nutrition. You can find a table of selenium-rich foods here.
The human body contains about 4 mg of selenium 1. Approximately 28 to 46% of that is stored in skeletal muscles 2. Higher amounts of selenium are also found in the liver, pituitary gland, thyroid gland, and kidneys 3.
Selenium is a component of the amino acid selenocysteine, which is incorporated into numerous selenoproteins. 4. So far, 25 selenoproteins have been scientifically described. 5. However, the exact functions of many of these proteins in the human body are still not fully understood. 6. Selenoproteins are building blocks of enzymes that are involved in various bodily functions.
Selenoproteins are also found in the enzyme glutathione peroxidase (GPx; a total of five different types present in the human body), 7. In this enzyme, selenium acts as a cofactor in a number of antioxidant processes. Glutathione peroxidase protects the cardiovascular system and muscles 8. Additionally, the enzyme helps in combating allergic and inflammatory diseases. Selenium helps protect the thyroid gland from free radicals. The enzymes catalyze the reduction of hydrogen peroxide (a cellular toxin) released as a byproduct during thyroid hormone synthesis 9.
In addition, selenoproteins are important for normal brain function. 10.
Selenoproteins also function as enzymes, acting as antioxidants that protect cell membranes from damage caused by oxidative stress from free radicals (reactive oxygen species) 11 12. Free radicals attack cells, impair their functionality, and damage the genetic material (DNA). As a result, errors in cell division may occur, potentially leading to malignant tumor diseases (cancer). Selenium also protects proteins and lipids from oxidative damage 13.
Iodothyronine deiodinases, a group of three enzymes containing selenoproteins, are responsible for the conversion of the thyroid hormone thyroxine (T4) into the biologically active form triiodothyronine (T3) 17. They are ultimately responsible for the activation and inactivation of thyroid hormones 18.
Another enzyme that contains selenium in the form of selenocysteine (a proteinogenic L-amino acid) is thioredoxin reductase. The enzyme catalyzes the reduction of oxidized thioredoxin and other proteins using NADPH (nicotinamide adenine dinucleotide phosphate) 19. It also plays an important role in the regeneration of some antioxidants, possibly including vitamin C 20.
Selenoproteins are also of great importance for male fertility and spermatogenesis as they improve fertility 21.
A selenium-rich diet supports the formation, metabolism, and protects the thyroid from excessive iodine consumption 22.
Selenium binds to metals such as mercury and cadmium in the body, which are then excreted 23. This reduces the risk of diseases that can arise from toxic heavy metals.
Many functions and benefits of selenium in the form of selenoproteins are not yet fully understood. These include those that are active in the heart, plasma, kidneys, and muscles 24.
Strengthening the immune system through selenium
Studies also attribute selenium with immune-strengthening properties. An improved activation and proliferation of B lymphocytes, which are a type of white blood cells necessary for antibody production, have been demonstrated 25. Selenium also enhances the activity of T cells and the cytotoxicity of natural killer cells 26.
Furthermore, scientists speculate that selenium supplementation at a daily dosage of 200 µg may enhance the anti-inflammatory activities in patients with autoimmune thyroiditis (also known as Hashimoto's thyroiditis) 27.
Protection against cancer?
Due to selenium's ability to protect against free radicals, this trace element is believed to have a certain protective benefits against the development of cancer.
However, several studies reveal different results. In 2003, a 49% reduced risk of prostate cancer was observed in men who supplemented with 200 µg of selenium daily 28. However, more recent study findings show no preventive effect of selenium on prostate cancer 29. According to studies, excessive selenium supplementation along with vitamin E in supplements actually increases the risk of prostate cancer 30. Scientists maintain that there is still no convincing evidence that selenium supplementation can prevent cancer 31.
Study findings from 2015 indicate that selenium and selenium compounds have a direct anti-cancer benefit and enhance chemotherapy, as well as neuroprotective and cytoprotective benefits 32.
Other study findings from 2015 suggest a connection between selenium and colorectal (affecting the colon and rectum) health 33. Higher selenium concentrations are associated with an 8% lower risk of colorectal cancer.
Function for Athletes
Selenium is involved in metabolic processes and can contribute to weight loss and muscle building. Additionally, the selenium-containing protein called selenoprotein-W has been discovered. Although its function is largely unknown, it may play a role in muscle metabolism (ATP production) 34.
A normal selenium level is important for bone mineral density 35. Bone health is dependent on thyroid function.
Selenium can be well absorbed by the body
Selenium found in food can be easily absorbed by the body. Over 90% of the amino acid selenomethionine (which contains selenium) present in plant-based foods is absorbed in the digestive tract 36. Plant-based foods also contain selenates and smaller amounts of selenocysteine, which are also well absorbed.
Considerations for Vegans
Many plant-based foods provide selenium. With a varied diet, rich in nuts like Brazil nuts, you can usually easily meet the daily selenium requirement and avoid selenium deficiency. However, the selenium content in these foods heavily depends on the selenium levels in the soils they grow on.