Autoimmune reactions may completely prevent the cells ability to produce intrinsic factor. After B 12 is absorbed, it is bound to serum protein globulins and is transported by the circulatory system to various tissues in the body. The highest concentrations of B 12 are found in the liver, kidneys, heart, pancreas, testes, brain, blood, and bone marrow. These body tissues are all related to red blood cell formation. The amount of B 12 absorbed by the body is regulated by intrinsic factor, which if absent causes pernicious anemia.
Absorption is better when the vitamin is taken throughout the course of the day.
Absorption decreases with age and with iron, calcium, and B 6 deficiencies and increases during pregnancy. An injectable form is usually used in order to bypass the absorption defect in pernicious anemia patients. Data suggests that if high enough doses of oral vitamin B 12 are used the results will be satisfactory. It is essential for the production of certain amino acids and fats and in the formation and maintenance of the nervous system. The entire B complex is crucial in the formation of neurotransmitters, which are chemicals that facilitate communication between nerve cells.