Vitamin B12 deficiency causes pernicious anaemia. Animals cannot synthesise vitamin B12. Humans must obtain all their vitamin B12 from their diet. The complexing metal ion in vitamin B12 is Co3+ (Cobalt ion). The vitamin B12 group of molecules are the only cobalt-containing molecules (called 'cobalamins') associated with biochemistry of humans. It is the cobalt (III) ion complex that gives this water-soluble vitamin its distinctive red colour.