Vitamin B12 isnecessary for the synthesis of red blood cells, the maintenance of the nervoussystem, and growth and development in children. FunctionsVitamin B12'sprimary functions are in the formation of red blood cells and the maintenenceof a healthy nervous system. B12 is necessary for the rapid synthesis of DNAduring cell division. B12 is also important in maintainingthe nervous system. B12 plays a vital role in the metabolism of fatty acidsessential for the maintainence of myelin. Absorption of B12 requires thesecretion from the cells lining the stomach of a glycoprotein, known asintrinsic factor. The B12-intrinsic factor complex is then absorbed in theileum (part of the small intestine) in the presence of calcium. Vitamin B12 can be stored in smallamounts by the body. Around 80% of this is stored in the liver. Vitamin B12 is excreted in the bileand is effectively reabsorbed. The amount of B12 excreted in the bile can varyfrom 1 to 10ug (micrograms) a day. However, it is thought that this is due tothe presence of compounds structurally similar to B12, known as B12 analogues. Researchers have suggested thatsupposed B12 supplements such as spirulina may in fact increase the risk of B12deficiency disease, as the B12 analogues can compete with B12 and inhibitmetabolism. Bacteria present in the largeintestine are able to synthesise B12.
This may be responsible for the lack ofaneamia due to B12 deficiency in vegan communities in developing countries. Boilingmilk can also destroy much of the B12. The RNI is theamount of nutrient which is enough for at least 97% of the population. Vitamin B12 functions as a methyl donor and works with folic acid in thesynthesis of DNA and red blood cells and is vitally important in maintainingthe health of the insulation sheath (myelin sheath) that surrounds nerve cells.The normal blood level of vitamin B12 ranges between 200 and 600 picogram/milliliter(148-443 picomol/liter). The amount of vitamin B12 actually needed by the body is very small,probably only about 2 micrograms or 2 millionth of a gram/day. The richestdietary sources of vitamin B12 are liver, especially lamb's liver, and kidneys.The actual absorption of B12 is also a problem with supplements. Somephysicians still maintain that monthly injections of vitamin B12 is required tomaintain adequate levels in the elderly and in patients with a diagnoseddeficiency