Vitamin B₁₂, vitamin B12 or vitamin B-12, also called cobalamin, is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins. It is normally involved in the metabolism of every cell of the human body, especially affecting DNA synthesis and regulation, but also fatty acid metabolism and amino acid metabolism. Neither fungi, plants, nor animals (including humans) are capable of producing vitamin B₁₂. Only bacteria and archaea have the enzymes required for its synthesis, although many foods are a natural source of B₁₂ because of bacterial symbiosis. B₁₂ is the largest and most structurally complicated vitamin and can be produced industrially only through a bacterial fermentation-synthesis.