- A cobalt-containing water-soluble vitamin (cobalamin) which together with folic acid has a vital role in metabolic processes and in the formation of red blood cells. It is responsible for the general feeling of well-being in healthy individuals. It is normally found only in animal products, particularly ox kidney and liver and oily fish. Vegetarians and vegans should take supplements which are produced by a fermentation process. Lack of vitamin B12 which may be due to its absence in the diet or poor absorption in the gut can cause a form of anaemia (Addison’s pernicious anaemia). It is normally prescribed together with folic acid.