What does the vitamin B12 do?

Vitamin B12 is used to treat vitamin B12 deficiency, cyanide poisoning, and hereditary deficiency of transcobalamin II. It is also given as part of the Schilling test for detecting pernicious anemia. For cyanide poisoning, a large amount may be given intravenously, and sometimes in combination with sodium thiosulfate. The mechanism of action is straightforward: the hydroxycobalamin hydroxide ligand is displaced by the toxic cyanide ion, and the resulting harmless B12 complex is excreted in urine. In the United States, the Food and Drug Administration approved (in 2006) the use of hydroxocobalamin for acute treatment of cyanide poisoning. High vitamin B12 level in elderly individuals may protect against brain atrophy or shrinkage, associated with Alzheimer's disease and impaired cognitive function. High-dose administration of Vitamin B12 has been additionally validated to stimulate the activity of the body's TH1 suppressor T-Cells, which then down-regulates the over-production of the allergen antibody IgE in allergic individuals.