• Vitamin B12 functions as a coenzyme in the conversion of homocysteine to methionine, in the metabolism of fatty acids and amino acids, and in the production of neurotransmitters. It also maintains a special lining that surrounds and protects nerve fibers, and bone cell activity depends on vitamin B12. Folate and vitamin B12 are closely related. • When folate gives up its methyl group to B12, it activates this vitamin. YOU NEED FOLIC ACID • The primary sources of vitamin B12 • Vitamin B12 is found only in foods of animal origin, except where plant-based foods have been fortified. Rich sources of vitamin B12 include shellfish, liver, game meat (venison and rabbit), some fish (herring, sardines, salmon, trout), milk and milk products.