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Vitamin B12 is a water-soluble vitamin that is stored in the liver. Vitamin B12 is a collective term for a group of cobalt-containing compounds known as corrinoids. The principal cobalamins are cyanocobalamin, hydroxocobalamin and the two coenzyme forms of vitamin B12, methylcobalamin and 5-deoxyadenosylcobalamin (adenosylcobalamin). Cyanocobalamin is the principal form of the vitamin used for fortification of foods and in nutritional supplements. Vitamin B12 is also called cobalamin because it contains the metal cobalt. Vitamin B12 is bound to the protein in food. Hydrochloric acid in the stomach releases B12 from proteins in foods during digestion. Hydroxocobalamin is a man-made form of vitamin B12. The advantage using hydroxocobalamin is the lack of adverse effects seen with the nitrites such as methemoglobinemia and hypotension. It works by exchanging the hydroxy group for cyanide to form the non-toxic cyanocobalamin (vitamin B12).
Cyanocobalamin is considered the most potent vitamin and is one of the last true vitamins that has been classified. Vitamin B12 combines with a substance called gastric intrinsic factor (IF). This complex can then be absorbed by the intestinal tract. Intrinsic factor is secreted by the stomach lining and it tightly binds vitamin B12 and helps it pass through the intestinal lining and into the blood. Any abnormal production of this intrinsic factor can result in vitamin B12 deficiency. Vitamin B12 is needed for normal nerve cell activity, DNA replication, and production of the mood-affecting substance SAMe (S-adenosyl-L-methionine). Vitamin B12 also works closely together with vitamin B9 (folate) to regulate the formation of red blood cells and to help iron function better in the body. Vitamin B12 is important for the activity of certain enzymes within cells that control fat, amino acid and carbohydrate metabolism (enzymes are special substances that speed up reactions in the body). Both vitamin B12 and the vitamin folate are essential for the production of genetic material in the body (DNA and RNA).
Vitamin B12 (cyanocobalamin, cobalamin) functions, uses, and health benefits
Vitamin B12's main functions are in the formation of red blood cells and the maintenence of a healthy nervous system. Vitamin B12 is an especially important vitamin for maintaining healthy nerve cells and it aids in the production of DNA and RNA, the body's genetic material. Cyanocobalamin works to promote normal growth and development, helps with certain types of nerve damage, and treats pernicious anemia. Vitamin B12 helps in the formation of red blood cells and in the maintenance of the central nervous system. Nerves are surrounded by an insulating fatty sheath comprised of a complex protein called myelin. B12 plays a vital role in the metabolism of fatty acids essential for the maintainence of myelin. Prolonged B12 deficiency can lead to nerve degeneration and irreversible neurological damage.
Vitamin B12 is essential for the proper production of blood platelets and red and white blood cells, the manufacture of vital substances needed for cell function, and the metabolism of nutrients necessary for cell growth. It participates in a variety of cellular reactions to release energy from carbohydrates, fats and protein. Vitamin B12 helps maintain the myelin sheath that insulates nerve fibres from each other. People with vitamin B12 deficiency show irregular destruction of the myelin sheaths, which eventually causes paralysis and death. Vitamin B12 levels decrease with age and various measures of cognitive impairment are associated with reduced B12 status. The most important use of vitamin B12 is to treat the symptoms of pernicious anemia. Vitamin B9 (folate) and vitamin B12 are critical to the health of the nervous system and to a process that clears homocysteine from the blood. Vitamins B12, B6, and B9 (folate) work closely together to control blood levels of the amino acid homocysteine. Elevated plasma homocysteine concentrations are considered to be a risk factor for vascular disease and birth defects such as neural tube defects.
Vitamin B12 (cyanocobalamin, cobalamin) dosage, intake, recommended daily allowance (RDA) Most people do not require vitamin B12 supplements. The recommended dietary intake for vitamin B12 is 2 micrograms per day for adults, but women who are pregnant require 3 micrograms per day and who are lactating require 2.5 micrograms per day. Absorption of vitamin B12 is reduced with increasing age. Elderly people may need greater amounts of vitamin B12 than younger people because the body's ability to absorb vitamin B12 from the diet diminishes with age. Older people have an overgrowth of bacteria in their stomachs. The bacteria that are usually killed by stomach acid compete for the vitamin B12 that is available and take it for their own use. Because vitamin B12 comes primarily from animal products, people who follow a strict vegetarian diet and do not consume eggs or dairy products may require vitamin B12 supplements.
Sources of vitamin B12 (cyanocobalamin, cobalamin)
Vitamin B12 is found naturally in food sources (principally animal products) in protein-bound forms. Animal products are the principal food sources of vitamin B12. B12 cannot be made by plants or by animals. Cyanocobalamin is the principal form of vitamin B12 used in nutritional supplements and for fortification of foods. Methylcobalamin is also available for nutritional supplementation and hydroxocobalamin is available for parenteral administration. Good sources of vitamin B12 include liver, tuna, cottage cheese, yogurt and eggs. Most standard multivitamin supplements also provide the recommended daily allowance of vitamin B12. Food-form B12 is comprised of protein-bound methylcobalamin and adenosylcobalamin. The only reliable unfortified sources of vitamin B12 are meat, dairy products and eggs.
Vitamin B12 (cyanocobalamin, cobalamin) deficiency
Vitamin B12 deficiency occurs when there is an abnormally low level of vitamin B12 absorbed in the body. The absorption of dietary vitamin B12 occurs in the small intestine and requires a secretion from the stomach known as intrinsic factor. If intrinsic factor is deficient, absorption of vitamin B12 is severely diminished. Vitamin B12 deficiency can be a factor in a variety of different health conditions and disorders. B12 deficiency inhibits of severy decrease the bodies ability to produce blood, increases blood cell destruction, and is very harmful to the nervous system. Characteristic signs of B12 deficiency include fatigue, weakness, nausea, constipation, flatulence (gas), loss of appetite, and weight loss. Symptoms of severe vitamin B12 deficiency (regardless of the cause) may include burning of the tongue, fatigue, weakness, loss of appetite, intermittent constipation and diarrhea, abdominal pain, weight loss, menstrual symptoms, psychological symptoms, and nervous system problems, such as numbness and tingling in the feet and hands.
Vitamin B12 (cyanocobalamin, cobalamin) overdose, toxicity, side effects
Vitamin B12 is considered safe and non-toxic. No toxic or adverse effects have been associated with large intakes of vitamin B12 from food or supplements in healthy people.