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 via the synthesis of myelin, and the formation of red blood cells. It is one of eight B vitamins. It is involved in the metabolism of every cell of the human body, especially affecting DNA synthesis, fatty acid and amino acid metabolism. No fungi, plants, or animals are capable of producing vitamin B₁₂. Only bacteria and archaea have the enzymes needed for its synthesis. Some substantial sources of B12 include animal products, fortified foods, and dietary supplements. B12 is the largest and most structurally complicated vitamin and is produced industrially only through bacterial fermentation. This B12 is used for fortified foods and supplements. It has also been produced synthetically via vitamin B12 total synthesis.