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Now regarded as an essential trace Elements in humans and animals, selenium is found in uneven quantities in parts of the earth’s surface. Selenium toxicity has been noted in areas where selenium content of the ground is high, but selenium deficiency is a far more widespread problem - contributing to Infertility, heart problems, eye disease and premature Aging.
Selenium carries out its main functions as part of the enzyme glutathione peroxidase. Glutathione peroxidase is an antioxidant that protects intracellular structures against oxidative damage by free radicals.
Selenium is known to have a role in the following:
Selenium deficiency has traditionally occurred in areas where the soil is particularly low in this mineral. However, as modern lifestyles have allowed us to eat foods from very many different countries of origin, true selenium deficiency has become less of a problem.
One selenium deficiency disease is known as Keshan’s disease - after the province in China that has the lowest soil selenium levels in the world. Symptoms are mainly to do with the heart - specifically involving wastage of the heart muscle.
Another selenium deficiency disease is known as Kaschin-Beck disease, and affects the cartilage in the joints.
Upper safe level for daily supplementation = 200µg
There is no EC Recommended Daily Allowance for selenium. The average daily intake from the diet = 65µg.
The groups of people particularly found to be at risk of selenium deficiency are as follows:
Any of the above groups may benefit from additional selenium in the form of supplement, although efforts should also be taken to improve the diet as well.
Evidence of disturbed selenium regulation occurs at intakes above 750µg and deterioration and loss of nails have been noted in adults ingesting 900µg per day.
There are no known drug interactions or contra-indications for selenium.
Vitamin E is a very important synergistic factor that enhances the benefits of selenium and vice versa.
Selenium and Chronic Heart Failure
Increased oxidative stress is involved in the pathogenesis of chronic heart failure (CHF), the common end result of most cardiac diseases. Selenium is an "essential" trace element, which means that it must be supplied by our daily diet and that its blood and tissue concentrations are low. Selenium has a variety of functions. It is a key component of several functional selenoproteins required for normal health. The best known of these are the antioxidant glutathione peroxidase (GPx) enzymes, which remove hydrogen peroxide and the harmful lipid hydroperoxides. GPx deficiency exacerbates endothelial dysfunction, a major contributing factor in the severity of CHF symptoms, in various conditions such as hyperhomocysteinemia. This suggests that homocysteine may be involved in the CHF associated endothelial dysfunction through a peroxide-dependent oxidative mechanism. Selenium also plays a role in the control of thyroid hormone metabolism and in protection against organic and inorganic mercury. Thus, selenium (through its role in selenoenzymes, thyroid hormones, and interactions with homocysteine and endothelial function) appears to be a major mediator in several pathways potentially contributing to CHF development.
Heart Fail Rev. 2006 Mar;11(1):13-7
Selenium is especially variable in plant foods, dairy products and eggs because of the tremendous variation in selenium content of the soil.
1. Kadrabová J. Selenium status, plasma zinc, copper, and magnesium in vegetarians. Biol Trace Elem Res, 50;1:13-24, 1995.