Selenium is a trace element that is essential in small amounts, but like all essential elements, it is toxic at high levels. Humans and animals require selenium for the function of a number of selenium-dependent enzymes, also known as selenoproteins. During selenoprotein synthesis, selenocysteine is incorporated into a very specific location in the amino acid sequence in order to form a functional protein. Unlike animals, plants do not appear to require selenium for survival. However, when selenium is present in the soil, plants incorporate it non-specifically into compounds that usually contain sulfur.
So what does selenium do?
In a nutshell, literally, selenium can help thyroid functioning, it has been shown to be effective in cancer prevention. It can help to reduce lipid oxidation (as in making cholesterol from good to bad). It maintains the antioxidant functions of vitamin E and C, and many other cellular functions are dependent on selenium.
How much do I need and where do I get it from?
Selenium is found mainly in some Brazil nuts (when grown in selenium rich soils) and shell fish. Most supplements do contain some selenium, but the forms differ greatly in absorbability. Only the Selenomethionine form is 90% absorbed, the other, less expensive forms, are barely absorbed if at all. So if your supplement contains sodium selenite, sodium selenate or salts such as selenium oxide, etc, then you are wasting your money.
It is recommended that an adult should have between 200 mcg up to 400 mcg of selenium daily. It is estimated that the average person gets about 70 mcg or less daily from diet. If you live, or consume foods, from depleted areas such as the US North West, North Central, and North East, AZ, NM, some areas of China, and New Zealand then you may be getting much less. The RDA is 40 mcg, so below that level problems with selenium deficiency can appear, but the benefits occur at levels over 200 mcg.
What do I do?
I take a twice daily multi-vitamin which provides me with 200 mcg of Selenomethionine per day. I also munch on a few nuts a day (brazil nuts are one of my favorites.) As I’ve often said make sure you take only pharmaceutical grade supplements so you are sure that if it says it contains 200 mcg of selenium that it actually does.
Below are more details about exactly what selenium does and tables of selenium rich foods and the upper limit for different age groups.
In conjunction with the compound thioredoxin, thioredoxin reductase participates in the regeneration of several antioxidants, possibly including vitamin C. Maintenance of thioredoxin in a reduced form by thioredoxin reductase is important for regulating cell growth and viability
The thyroid gland releases very small amounts of biologically active thyroid hormone (triiodothyronine or T3) and larger amounts of an inactive form of thyroid hormone (thyroxine or T4) into the circulation. Most of the biologically active T3 in the circulation and inside cells is created by the removal of one iodine atom from T4 in a reaction catalyzed by selenium-dependent iodothyronine deiodinase enzymes. Three different selenium-dependent iodothyronine deiodinases (types I, II, and III) can both activate and inactivate thyroid hormone by acting on T3, T4, or other thyroid hormone metabolites. Thus, selenium is an essential element for normal development, growth, and metabolism because of its role in the regulation of thyroid hormones
Selenoprotein P is found in plasma and also associated with vascular endothelial cells (cells that line the inner walls of blood vessels). The primary function of selenoprotein P appears to be a transport protein for selenium (6). It also functions as an antioxidant that protects endothelial cells from damage induced by such compuonds as peroxynitrite.
15 kDA selenoprotein (Sep15) is mammalian protein located inside the cell. Here, it binds UDP-glucose:glycoprotein glucosyltransferase, an enzyme that senses protein folding. Sep 15 has a redox function and is also implicated in cancer prevention.
Antioxidante properties – Selenium works in conjunction with other minerals (copper, zinc, iron) and support the activity of vitamin E in limiting the oxidation of lipids (fats) It is the oxidation of the lipid cholesterol which causes LDL cholesterol to become sticky and become “bad”. Selenium also matins the antioxidant function of Vitamin C.
Selenium deficiency may exacerbate the effects of iodine deviancy.
Selenium deficiency results in decreased activity of the several enzymes. Even when severe, isolated selenium deficiency does not usually result in obvious clinical illness. However, selenium-deficient individuals appear to be more susceptible to additional physiological stresses.
several diseases which are found to be common in areas where the soil is selenium deficient are Keshan disease, a cardiac disease. Kashin-Beck disease is characterized by the degeneration of articular cartilage between joints (osteoarthritis) and is associated with poor selenium status in areas of northern China, North Korea, and eastern Siberia
Selenium deficiency has been associated with impaired function of the immune system. Moreover, selenium supplementation in individuals who are not overtly selenium deficient appears to stimulate the immune response
There is a great deal of evidence indicating that selenium supplementation at high levels reduces the incidence of cancer in animals. More than two-thirds of over 100 published studies in 20 different animal models of spontaneous, viral, and chemically induced cancers found that selenium supplementation significantly reduces tumor incidence. Geographic studies have consistently observed higher cancer mortality rates in populations living in areas with low soil selenium and relatively low dietary selenium intakes.
Some studies have reported that low dietary selenium intakes are associated with increased risk of prostate cancer. A case-control study within a prospective study of over 50,000 male health professionals in the U.S. found a significant inverse relationship between toenail selenium content and the risk prostate cancer.
Sources of Selenium:
|Brazil nuts (from selenium-rich soil)
||1 ounce (6 kernels)
||3 ounces (10-12)
||1 cup, cooked
||1 cup, cooked
|Chicken (light meat)
|Whole wheat bread
||8 ounces (1 cup)
||1 ounce, shelled
Selenium supplements are available in several forms. Sodium selenite and sodium selenate are inorganic forms of selenium. Selenate is almost completely absorbed, but a significant amount is excreted in the urine before it can be incorporated into proteins. Selenite is only about 50% absorbed but is better retained than selenate once it is absorbed. Selenomethionine, an organic form of selenium that occurs naturally in foods, is about 90% absorbed. Selenomethionine and selenium-enriched yeast, which mainly supply selenomethionine, are also available as supplements. The consumer should be aware that some forms of selenium yeast on the market contain yeast plus mainly inorganic forms of selenium. Both inorganic and organic forms of selenium can be metabolized to selenocysteine by the body and incorporated into selenoenzymes
|Tolerable Upper Intake Level (UL) for Selenium
|Infants 0-6 months
|Infants 6-12 months
|Children 1-3 years
|Children 4-8 years
|Children 9-13 years
|Adolescents 14-18 years
|Adults 19 years and older