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What is it?

B12 and folate are B complex vitamins that are necessary for normal red blood cell formation, tissue and cellular repair, and DNA synthesis. A B12 and/or folate deficiency reflects a chronic shortage of one or both of these vitamins. Since the body stores from three to five years' worth of B12 and several months’ supply of folate in the liver, deficiencies and their associated symptoms can take months or years to manifest in adults. Infants and children show signs of deficiency more rapidly, however, as they have not yet built up extensive reserves.

Physiology of B12 absorption

The absorption of ingested vitamin B12 is complex and the vitamin B12 is bound to a succession of proteins as it makes its way from the mouth to the terminal ileum where it is absorbed and enters the bloodstream. The most important of these from a clinical point of view is intrinsic factor secreted by the parietal cells of the stomach. This is because intrinsic factor binding is defective in pernicious anaemia. The B12-intrinsic factor complex is then absorbed from the terminal ileum part of the intestine, bound to transcobalamin II, the plasma transporter, taken into cells, broken down and free B12 is released into the cytoplasm of cells.

Deficiency of B12 or folate

Over time, a deficiency in either B12 or folate can lead to macrocytic anaemia, a condition characterised by the production of fewer but larger red blood cells with a decreased ability to carry oxygen. People with anaemia may be weak, light-headed and short of breath. A deficiency in B12 can also result in varying degrees of neuropathy - nerve damage - that can cause tingling and numbness in the hands and feet and mental changes that range from confusion and irritability to severe dementia.

Pregnant women need increased amounts of folate for proper fetal development. If a woman has a folate deficiency prior to pregnancy, it will be intensified during gestation and may lead to premature birth and neural tube birth defects, such as spina bifida, in the child.


Last Review Date: March 19, 2016