Vitamin B12 is named after the rare earth metal at its center
Vitamin B12 is the collective term for a group compounds known as cobalamin (because they contain the mineral cobalt). The two main forms of cobalamin are cyanocobalamin and hydroxycobalamin and there are two 'co-enzyme' forms called methylcobalamin and adenosylcobalamin. There is a good reason for why there are different forms of B12.
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