Selenium is a trace element essential for the body and health thanks to its antioxidant, anti-inflammatory and anti-tumor action, it is also beneficial for the heart, the immune system and the thyroid. Selenium was first described in 1817 and owes its name to the Greek term selene, which indicates the moon, referring to the light and silvery color that selenium assumes when it is melted and then cooled. In the past it was erroneously believed that selenium was toxic, however, in the 60s, this belief was completely overturned thanks to scientific studies that understood the real beneficial action of selenium when it is taken at the correct doses avoiding excesses. But let's try to understand better.
This element is fundamental for the synthesis of particular proteins, called selenoproteins, involved in different processes of the organism. In fact, selenoproteins counteract free radicals and inflammations and are also involved in the production of thyroid hormones and in the antioxidant processes affecting the thyroid (Ventura et al, Int J Endocrinol, 2017). A lack of selenium is associated with a weak immune response, cognitive decline and an increased risk of mortality, while high selenium values help fight viruses, protect the reproductive processes and reduce the risk of autoimmune diseases of the thyroid.
Moreover, selenium has proved to be protective against certain types of tumors such as prostate, colon, lung and bladder (Rayman et al, Lancet, Mar 2012).
Selenium, requirements and dietary sources
In the adult the daily requirement is between 0.05 and 0.07 mg, it depends on the guidelines of the different Countries (Ventura et al, Int J Endocrinol, 2017). A varied diet guarantees the correct intake of selenium. In fact, selenium is found in the soil on which plants and cereals grow.
Then, we eat these plants or the derived products of the animals that eat these plants. In this way we can bring selenium in our body. Food sources of selenium are Brazil nuts, two per day are enough, seeds, unrefined grains, especially barley, meat, for example beef and chicken, fish, especially cod, mollusks and tuna, leafy greens, shiitake mushrooms, champignons and milk (Thomson et al, Am J Clin Nutr, Feb 2008 - Stoffaneller et al, Nutrients, 2015 - USDA Food Composition Database).
Selenium and supplements, when to take them and risks
In general, thanks to a varied diet, it is not necessary to use selenium supplements. However, in some cases such as chronic inflammatory processes, which cause a lowering of selenium values, long drug therapies, recurrent infections, advancing age, it may be useful, after asking your doctor for advice, to take selenium in the form of supplements. In any case, be always careful with selenium supplements. Avoid DIY because, if a selenium deficiency is to be avoided, it is equally undesirable to have too high levels of selenium. In fact, when the selenium introduced with the diet already guarantees correct values of this element, further selenium supplements, besides the fact that they do not bring additional benefits, are also considered the cause of an increased risk of developing type 2 diabetes and, in case of very high levels of this mineral, also of abdominal pain, nausea, vomiting (Rayman et al, Lancet, Mar 2012 - Duntas et al, Endocrine, Apr 2015). These considerations, however, are referring just to the supplements and not to the diet.