Vitamin B12, found only in foods of animal origin, is unique among vitamins as it contains the metal ion cobalt. For this reason compounds having vitamin B12 activity are called ‘cobalamin’.

 

In the human body, the vitamin B12 forms ‘methylcobalamin’ and ‘5-deoxyadenosyl cobalamin’ are used. Most supplements contain the form ‘cyanocobalamin’, which is converted in the body (1).