Vitamin B12
Food sources of vitamin B12
In mg per 100g:
* Cyanobacteria
o Arthrospira platensis: 290
* Meat
o Beef Liver: 110
o Liver of sheep: 65
o Liver Veal: 60
o Kidneys Beef: 35
o Kidney of calf: 25
o Chicken liver: 20
o pig kidneys: 15
* Fish
o Herring: 15
o Oysters: 15
o Mackerel: 12
o Dried Cod: 10
o Crab: 10
o Sardine: 10
o Salmon: 7
o Thon: 4
* Dairy products
o Cream Cheese: 8
* Eggs 1.3 mcg
Vitamin B12 is very little (or not) in the plant world: the comfrey and most edible seaweed such as 'porphyry' (Porphyra umbilicalis) were deemed to occur, but these results are Aujoud set aside. The current consensus in the scientific community is that these molecules are not equivalent variants of the human vitamin. There is a consensus and the literature contains contradictory publications on the topic, even if today the consensus seems to emerge. The importance of disorders caused by deficiency of vitamin B12 called for greater caution in vegans: It is strongly recommended that they use vegan vitamin supplements or B12 fortified foods vegan (soy milk, steaks, vegetables, etc. ...). Most associations recommend vegan vegans ensure their vitamin B12, including the Vegan Society, Vegan Association is the oldest (founded in 1944 in the United Kingdom).
Vitamin B12
Vitamin B12 (or cobalamin) is a water-soluble vitamin ensuring good manufacturing of neurotransmitters. Vitamin B12 is the cofactor of enzymes involved in metabolism of nucleic acids and synthesis of methionine. This vitamin is also essential to maintaining the integrity of the nervous system and especially the myelin sheath that protects nerves and enhances their functioning.
It exists in several forms belonging to the family of cobalamin: cyanocobalamin, hydroxocobalamin, methylcobalamin and adenosylcobalamin. Cyanocobalamin and hydroxocobalamin are its stable forms. The cobalamins have a similar chemical structure of heme, but the central iron atom is replaced by a cobalt atom, hence the name of cobalamins.
A vitamin B12 deficiency causes a form of anemia called pernicious anemia (or pernicious anemia), one of whose features is the presence of red blood cells significantly increased in size (macrocytosis).
Discovery of vitamin
The original research on the vitamin begins with a description of a fatal anemia, pernicious anemia, by different authors including Thomas Addison and Michael Anton pernicious in the nineteenth century.
Around 1920, George Whipple, George Minot and William Murphy (Nobel Prize 1934) showed that liver extracts as food supplements were capable of correcting certain anemias. The liver extracts contain the extrinsic factor, that is to say, vitamin B12 itself.
William Castle has shown that there is a critical intrinsic factor, and nonexistent in patients suffering from pernicious anemia and an extrinsic factor from food (liver, meat).
Vitamin B12 was isolated in 1948 by Karl Folker Laboratory Merck and Lester Smith of Glaxo. The three-dimensional pattern was identified by Dorothy Hodgkin. (Nobel Prize in Chemistry in 1964)
In 2007, researchers from MIT and Harvard Medical School have discovered the secret of the synthesis of vitamin B12.
Physiology
The human body does not synthesize vitamin B12. In nature this synthesis is performed by bacteria, lower fungi and algae. Herbivores are able to absorb vitamin B12 produced by bacteria in their stomachs. Carnivores get their eating herbivores. For humans, the main sources are meat, fish, milk and eggs.
Vitamin B12 food is absorbed by a multi-step process. In the acidic stomach, it is separated from the food substrate by gastric pepsin. It then binds to salivary R protein which it is released into the duodenum as a result of pancreatic proteases. It can then be associated with intrinsic factor, a glycoprotein secreted by connecting the parietal cells of the stomach. The complex of vitamin B12 and intrinsic factor traverses the entire small intestine before being absorbed in this form in the distal ileum. The assimilation of vitamin B12 is compromised when one of the above mechanisms is lacking, such as when the stomach does not produce intrinsic factor.
Read also Vitamin K
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