When someone is vitamin B12 deficient, one of the reasons could be that the person’s digestive system (intestine) is not absorbing the vitamin efficiently.
Vitamin B12, also called cobalamin, is a water-soluble vitamin that is essential for the normal functioning of the brain (it participates in the synthesis of neurotransmitters), the nervous system (it is essential for maintaining the integrity of the nervous system and especially the sheath myelin that protects the nerves and optimizes their functioning) and the formation of blood (helps with the division of erythroblasts). It is one of the eight B vitamins. It is normally involved as a cofactor in the metabolism of each of the cells of the human body.
Dietary vitamin B12 is absorbed through a multi-step process. In the acidic environment of the stomach, it is separated from the food substrate of animal origin by gastric pepsins. It then binds to salivary R proteins from which it is released in the duodenum under the effect of pancreatic proteases. It can then associate with the intrinsic factor, a binding glycoprotein secreted by the parietal cells of the stomach. Vitamin B12-intrinsic factor complex travels throughout the small intestine before being absorbed in this form into the ileum via the cubam receptor.