Vitamin B12 is a water-soluble vitamin that plays a role in the human body as a cofactor of two enzymes: methionine synthase and the L-methylmalonyl-CoA mutase. It is indispensable in all cell division processes, for growth, and in addition to folic acid and iron, it is essential for the formation of red blood cells. It is also essential in the metabolism of carbohydrates, lipids, proteins, and necessary for the synthesis of purine and thymidine. It is needed for the proper functioning of the thyroid, it boosts the immune system and reduce fatigue. Vitamin B12 has a key role in the normal function of the brain, the myelination of nerve fibers, cognitive functions and other functions. The vitamin B12 deficiency may be due to malfunctioning of several sections of the gastrointestinal tract, since normal absorption of vitamin B12 requires a healthy stomach, pancreas, and small intestine. In spite of all the important roles that this complex vitamin has, the daily recommendation according to the DACH is 3 µg only. The only satisfying and reliable natural source is food of animal origin. Other sources like fermented soy products, black tea, some mushrooms, algae and vegetables which is fertilized with organic fertilizers or hydroponic cultivation and enriched with vitamin B12, are unimportant from nutritional aspect. From the point of view of supply of vitamin B12, the only reliable replacement for food of animal origin are preparations with vitamin B12, whose industrial production is based on microbiological biosynthesis, while the chemical synthesis is uneconomical and extremely demanding.