Selenium and its Relationship to Cancer
P. D. Whanger
Department of Environmental and Molecular Toxicology
Oregon State University
Corvallis, OR 97331
The statements "Selenium may reduce the risk of certain cancers" and "Selenium may produce anticarcinogenic effects in the body" are supported by scientific evidence. There is significant scientific agreement that daily supplementation with selenium may reduce the risk of some cancers and that selenium is anticarcinogenic. This report will examine epidemiological studies, human clinical trials, animal studies, and in vitro studies on selenium's relationship to cancer. It will examine the efficacy of different forms of selenium and of different levels of selenium supplementation.
Selenium is classified in a group VIA of the periodic table of elements which includes the nonmetals, sulfur and oxygen, in the periods above selenium, and the metals, tellurium and polonium, in the period below this element (Combs and Combs, 1986a). By period, selenium lies between the metal arsenic and the nonmetal, bromine. Thus, selenium is considered a metalloid, having both metallic and nonmetallic properties. It has an atomic number of 34 and an atomic weight of 79. Elemental selenium, like its sister elements, sulfur and tellurium, can exist in either an amorphous state or one of three crystalline states.
Elemental selenium can be reduced to the -2 oxidation state (selenide), or oxidized to the +4 (selenite) or +6 (selenate) oxidation states. Hydrogen selenide (H2Se) is a fairly strong acid in aqueous systems. The gas is colorless, has an unpleasant odor, and is highly toxic. At low pH, selenite is readily reduced to the elemental state by mild reducing agents such as ascorbic acid or sulfur dioxide. In its oxidized state (+6), selenium can exist as selenic acid or as selenate salts. Selenic acid is a strong acid. Most selenate salts are soluble in water, in contrast to the corresponding selenite salts and metal selenides. Selenates tend to be rather inert and are very resistant to reduction.
The chemical and physical properties of selenium are very similar to those of sulfur. The two elements have similar outer-valence shell electronic configurations and atomic sizes and their bond energies, ionization potentials and electron affinites are virtually the same. Despite these similarities, the chemistry of selenium and sulfur differ in two respects that distinguish them in biological systems. First, in the biological systems, selenium compounds are metabolized to more reduced states whereas sulfur compounds are metabolized to more oxidized states. The second important difference in the chemical behaviors of these elements is in the acid strengths of their hydrides. The hydride, H2 Se, is much more acidic than is H2S. This difference in acidic strengths is reflected in the dissociation behaviors of the selenohydryl groups of selenocysteine and the sulfhydryl groups on cysteine. Hence, while thiols such as cysteine are predominantly protonated at physiological pHs, the selenohydryl groups of selenols such as selenocysteine are predominantly dissociated under the same conditions.
II. Selenocompounds in plants.
The metabolism of selenocompounds in plants has been summarized (Whanger, 1989). Selenium enters the food chain through incorporation into plant proteins, mostly as selenocysteine and selenomethionine (Semet) at normal selenium levels. However, with elevated selenium levels, Se-methylselenocysteine (SeMCYS) can be the predominant selenocompound. As many as eight other selenocompounds have been identified in plants but their concentrations are usually very low except at high selenium levels. Indicator plants (called selenium accumulators) can accumulate extremely large amounts of selenium, ranging from 1000 to 10,000 Fg selenium per gm because they synthesize mostly nonprotein selenoamino acids (Brown and Shrift, 1981). As much as 80% of the total selenium in some accumulator plants is present as SeMCYS and until recently it was thought to be absent in nonaccumulator plants.
The selenium content of plants is dependent upon the region of growth (summarized by Whanger, 1989). Vegetables such as rutabagas, cabbage, peas, beans, carrots, tomatoes, beets, potatoes, and cucumbers contained a maximum of 6 Fg selenium per gm even when grown on seleniferous soils. Vegetables such as onions and asparagus may accumulate up to 17 Fg selenium per gm when grown on these types of soils. Plants which contain deficient levels of selenium are found in the Pacific Northwest, upper Mid-West, the New England states and along the Atlantic coast of the United States. In other parts of the country such as North and South Dakota, Colorado and Western Nebraska plants may contain high levels of this element. Plants can synthesize organic selenium compounds including Semet from inorganic selenium (Burnell and Shrift, 1977). Because of the uneven global distribution of selenium, disorders of both selenium deficiency and selenium excess are known. For example, China has regions with both the lowest and the highest selenium-containing soil in the world (Yang et al, 1989 a,b). Plants of economic importance do not have a selenium requirement for growth and thus plant selenium is for the health of animals including humans.
Although the data are lacking, synthesis of the nonprotein selenoamino acids by plants probably occurs along pathways normally associated with sulfur metabolism. Conversion of selenocysteine to SeMCYS in accumulators has been shown to involve the transfer of a methyl group from S-adenosylmethionine, analogous to the synthesis of S-methylcysteine (Neuhierl et al, 1999). Even though the primary source of selenium in soil is inorganic, mostly selenate, Astragalus accumulators have been shown to synthesize SeMCYS when supplied with Semet (Chen et al, 1970). The ability of the accumulators to exclude selenoamino acids from proteins has been suggested as a reason for their selenium tolerance. Similar mechanisms apparently operate in selenium enriched plants such as garlic, broccoli, onions and wild leeks where the nonprotein selenoamino, SeMCYS, is the predominant one present.
Most of the selenium in enriched wheat grain (Olson et al, 1970), corn and rice (Beilstein et al, 1991) and soybeans (Yasumoto et al, 1984) is Semet. Semet is the predominant form of selenium in selenium enriched yeast (Ip et al, 2000a). Selenium enriched yeast is the most common source of selenium available commercially (Schrauzer, 2000). The selenoamino acid, Semet, is also available for the public. The major form of selenium is SeMCYS in selenium enriched garlic (Ip et al, 2000a), onions (Cai et al, 1995), broccoli florets (Cai et al, 1995) and sprouts (Finley et al, 2001), and wild leeks (Whanger et al, 2000).
Part 2 of Selenium Study
Phil D. Whanger
Department of Environmental and Molecular Toxicology
Oregon State University
A copy of my curriculum vitae is attached
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 These results are consistent with some animal data. Hairless mice treated by topical application of selenomethionine (0.02%) or given drinking water with 1.5 micrograms selenium per ml as selenomethionine had significantly less skin damage due to ultraviolet irradiation (Burke et al, 1992b). This is consistent with an earlier study which indicated that dietary selenium (one microgram/g) fed to mice significantly reduced the number of skin tumors induced by two carcinogenic chemicals plus croton oil (Shamberger, 1970).
 The incidence of breast cancer is greatest of all cancers in women but it is the third highest cause of all cancer deaths (American Cancer Society, 2000), probably reflecting the improved methods for detecting and treatment of breast cancer compared to other cancers . Although usually not mentioned, a small number of men develop breast cancer with even some deaths. About 400 men die of breast cancer each year compared to 43,300 breast cancer deaths in women.
 The author is aware of a person who consumed one mg of selenium for two years before toxic signs of selenium occurred. Thus this element appears not as toxic as often believed.
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Look also at our Liquid Gluco Gel with MSM, Glucosame Sulfate, Chondroitin Sulfate, Cetylmyristoleate, and Collagen Hydrolysate. Check out Liquid Osteo fx an easy way to get your 1200mg of Daily Calcium with MSM and Glucosame Sulfate.
Pig Pack Wholesale Price:164.95