Selenium: An essential trace mineral nutrient

  • Selenium is a vital trace element nutrient with multiple roles in the growth and functioning of living cells of higher animals and humans. This element is unevenly distributed in the earth’s crust
  • Almost all of the selenium in animal tissue is found in the proteins. Some of these proteins contain stoichiometric quantities of selenium and are known as selenoproteins. Similarly, other proteins contain variable amounts of selenium (which substitutes sulfur randomly in the original protein) and are known as selenium-binding proteins
  • At the molecular level, selenium (as selenocysteine) is an essential component of the active sites of antioxidant enzyme glutathionine peroxidase, and the enzymes participating in thyroid functions – iodothyronine 5-deiodinase and mammalian thioredoxin reductase. Selenium is also present in several other mammalian selenoproteins. Lastly, selenium occurs in foods in the form of the seleno-amino acids (selenomethionine and selenocysteine) and their derivatives
  • Both glutathione peroxidase and thioredoxin reductase catalyze reactions essential to the protection of cellular components against oxidative and free radical damage
  • In recent years, laboratory experiments, clinical trials, and epidemiological data have established the role of selenium in the prevention of a number of degenerative conditions including cancer, inflammatory diseases, cardiovascular, neurological diseases, aging, infections, etc. Most of these effects are related to the function of selenium in the antioxidant enzyme systems
Background
  • Berzelius, a Swedish chemistry professor, discovered selenium in 1817. The mineral is present in the earth’s crust and is chiefly derived as a by-product of the copper refinery. Depending on soil composition, selenium is most abundant in foods such as meats, fish and grains
Benefits
  • For more than 40 years, selenium has been recognized as an essential nutrient. In 1957, Schwartz and Foltz established selenium as an essential trace element in nutrition for the prevention of disease
  • Low dietary levels of selenium in animals and humans have been linked to several disease symptoms. In animals, selenium deficiency has been associated with muscular dystrophy in sheep calves, liver necrosis in rats, liver and heart necrosis in pigs, and pancreatic atrophy and exudative diathesis in chicks. Human selenium deficiency has been documented in the pathogenesis and pathology of Keshan disease; a heart ailment observed in people of the Chinese province of Keshan, a region whose soil lacks adequate selenium levels. Myositis (muscle diseases characterized by inflammation and degenerative changes), psuedoalbinism, whitening of the fingernail beds, elevated creatinine kinase derived from muscles, macrocytosis (the presence of abnormally large red cells in the blood), osteathropathy (Kashi-Beck disease), and an increased incidence of cardiovascular disease and cancer in humans are also associated with low selenium levels
Organic vs Inorganic
  • Plants absorb selenium from the soil and convert them into organic forms that are easily assimilated. For example, L-(+)- selenomethionine, and organic compound, is the predominant form of selenium in wheat and cereals. L-(+)- selenomethionine is rapidly and completely absorbed from the gastrointestinal tract
  • Inorganic forms of selenium include sodium selenite and sodium selenate; they are not normal food forms of selenium. In comparing L-(+)- selenomethionine (LSM) with its inorganic counterparts the following was determined
    1. LSM is significantly better absorbed and retained in the body than sodium selenite
    2. In experimental animals supplemented with LSM, sodium selenite and selenocysteine, the highest increase in tissue selenium levels was accomplished with LSM. In addition, studies have suggested that LSM has a slower, whole-body turnover in comparison to sodium selenite. This means there is greater efficiency in the utilization of selenium in complex with methionine. Due to the role of methionine in aiding the safe metabolism of selenium, LSM is recognized as safer from of selenium than sodium selenite
Research
  • A large number of research papers are published on selenium annually. Cancer prevention, antiviral defense, immune-system enhancement, arthritis, and coronary disease are some of the areas that have been explored. Of the studies conducted on the therapeutic benefits of selenium, Clark et al. work serves as a landmark study. This 10-year study established selenium as an anticarcinogen in humans. Although selenium supplementation did not significantly affect the incidence of basal cell or squamous cell skin cancer, it did significantly reduce total cancer mortality, total cancer incidence, and incidences of lung, colorectal, and prostate cancers in the selenium-treated groups. Because selenium’s effects on these cancers were not the original focus of the study, critics argue that this study does not confirm selenium’s beneficial effects on cancer. Thus, this study has generated interest in funding follow-up research on selenium.
  • One follow-up study, funded by the National Cancer Institute (NCI) and coordinated by the Southwest Oncology Group (SWOG), is known as SELECT (Selenium and vitamin E Cancer Prevention Trial). It is a 12-year, prostate cancer study conducted with 32,000 men from the United States, Canada, and Puerto Rico. The IND number for this study is #58,212. The exclusive form of selenium chosen and used by NCI for this study is Sabinsa’s Selenium SeLECT®. Sabinsa is contracted to supply capsules of Selenium SeLECT® as well as the placebo for the trial
  • Selenium SeLECT®, a registered trademark of Sabinsa Corporation, is supplied in two grades as an organic, bioavailable, fully complexed (not a dry blend of selenium and methionine) form of selenium. Selenium SeLECT® Pure contains a minimum of 400,000 μg of elemental selenium (40%) per gram, and Selenium SeLECT® 5000 (a dicalcium phosphate trituration), containing a minimum 5,000 μg of elemental selenium (0.5%) per gram. Both grades are yeast and allergen-free and conform to USP monograph standards