Vitamin B12 is an chemical compound.
Vitamin . Vitamins are classified by their biological and chemical activity , not their structure . Vitamin B12 , also called cobalamin , is a water-soluble vitamin that has a key role in the normal functioning of the brain and nervous system , and the formation of red blood cells . Vitamin B12 consists of a class of chemically related compounds ( vitamers ) , all of which show pharmacological activity . It contains the biochemically rare element cobalt ( chemical symbol Co ) positioned in the center of a planar tetra-pyrrole ring called a corrin ring .