Selenium Supplements: Relative Bioavailability


Selenium Supplements: Relative Bioavailability



	Selenium is a vital trace element nutrient with multiple roles in the growth and functioning of living cells in higher animals and humans. This element is unevenly distributed in the earth's crust.

	The primary nutritional source is the soil from which it is absorbed by plants and enters the food chain. Geographical variations in the selenium status of populations therefore exist, necessitating selenium supplementation. The recommended levels for selenium supplementation in humans are 50-200 mcg/day.

	Very low selenium status is a factor in the etiologies of a specific type of juvenile cardiomyopathy (Keshan's Disease) and a chondrodystrophy (Kaschin-Beck Disease) that were observed in selenium-deficient regions of China.

Selenium supplements include:


	Inorganic salts such as sodium selenite and sodium selenate
	Selenium-amino acid chelates (such as aspartate)
	L-(+)-Selenomethionine
	Selenium yeast (where selenium is present as L-(+)-Selenomethionine).

Selenium SeLECT Vs Other forms of Selenium

supplementation:


	Inorganic selenium salts and chelated forms of selenium (chelates, aspartates) are broken down into elemental selenium. It is important to note that elemental selenium is not bioavailable and may have toxic effects at levels only four to five times the amount normally ingested in the human diet.


	Selenium SeLECT contains selenium in a molecularly integrated form and is therefore directly incorporated into the proteins in the body in place of the amino acid, methionine.




	Amino acid chelates and inorganic selenite / selenate are poorly bioavailable and may have toxic effects at levels only four to five times the amounts normally ingested in the human diet. Sodium selenate is almost completely absorbed, but a significant fraction is lost in the urine before it can be incorporated into the body tissues.

	Over 95% of the selenium in selenium yeast supplements is present in the form of Selenium SeLECT .

Metabolism Of Selenium SeLECT .


	L-(+)-Selenomethionine has the sulfur atom in L-(+)-Methionine replaced by selenium. It is converted to selenocysteine in the body. Selenocysteine is then incorporated into selenoproteins. The sequence is schematically represented in the figure below:



	It is reported that the replacement of methionine by selenomethionine in the protein structure does not induce any functional changes in the protein molecule.

	In fact, selenium in the protein structure protects the DNA from oxidation more efficiently than the original sulfur in methionine.

	The carbon-selenium bond is more easily broken during photochemical reactions as compared to the carbon-sulfur bond. Thus Selenium SeLECT preferentially "accepts" the energy from light. Therefore topical or orally administered Selenium SeLECT offers greater protection to the skin against damage by ultraviolet light.

	It is reported that selenium levels in the red blood cells of subjects treated with selenomethionine (in the form of selenium yeast) increased by100% after 16 weeks' supplementation. Neither selenite nor selenate supplementation produced significant increases under the same conditions. Thus selenomethionine and yeast containing selenomethionine are the appropriate forms of selenium for use in nutritional supplements and foods including infant formulas.

	However, if selenomethionine is supplied in the form of selenium yeast, it is important to ascertain that the selenium in the yeast is present in the form of L-(+)-Selenomethionine . Good commercial samples of selenium yeast typically contain 1000-2000 ppm of selenium, most of which is in the form of L-(+)-Selenomethionine . However, some samples may contain substantial amounts of inorganic selenium compounds instead of L-(+)-Selenomethionine .


Relative Bioavailability:


	Selenomethionine was found to be four times as effective as selenite in preventing the characteristic pancreatic degeneration caused by selenium deficiency in chicks.

	In a clinical study in China, selenium levels in both the blood plasma and erythrocytes of human volunteers increased at a significantly faster rate when they were given Selenium SeLECT as compared to the levels with inorganic compounds.

	Organic selenium, as selenium yeast (selenomethionine) was found to be much more effective than inorganic selenium compounds in increasing the selenium concentration of cow’s milk. Sodium selenite and sodium selenate had only a marginal effect on milk selenium concentration.