Introduction to Vitamin B12
Vitamin B12 is an alternative name for a water-soluble vitamin called cobalamin. It is found in a variable amount in meat, poultry, fish and dairy products. It is not found in plants and this is why vegans are more likely to suffer from its deficiency.
Vitamin B12 is aimed to perform the following two main functions in our body.
- Synthesis of new red blood cells
- Adequate functioning of Nervous system
Thus any deficiency of vitamin B12 will cause anemia in addition to the neurological manifestations.
It is estimated that our body stores vitamin B12 that is sufficient enough to fulfill its requirements for about 4 years even if we absolutely stop taking it. However still vitamin B12 deficiency can still occur secondary to either a decreased absorption or a decreased intake of vitamin B12 and can cause disorders related to blood and nervous system.
How Does Pernicious Anemia Lead to Vitamin B12 Deficiency?
Normally the vitamin B12 coming from the animal food is protein bound. This protein-bound vitamin B12 upon reaching the stomach is acted upon by the stomach acid and enzymes resulting in liberation of the vitamin B12 from the protein carrying it. However, this protein-free vitamin B12 is not yet ready for absorption and for that it needs to be processed further before it could be finally absorbed.
The parietal cells in our stomach are aimed to produce not only Hydrochloric acid but also the intrinsic factor, specialized proteins that are essential for the absorption of dietary vitamin B12. The problem in the case of Pernicious anemia somehow lies at the level of these parietal cells.
In the case of pernicious anemia, our own immune system mistakenly responds towards these parietal cells in one of the following ways.
- It recognizes the parietal cells as foreign entities and starts producing antibodies against them so that we could get rid of them. This causes the destruction of parietal cells, resulting in IF as well as HCL deficiency.
- Producing antibodies directed against IF itself. In this case, although the parietal cells remain intact, these auto-antibodies bind to IF, preventing it from binding to vitamin B12.
- In certain cases, the immune system may not have any problem with the binding of the IF with vitamin B12. Thus vitamin B12 may perfectly bind to intrinsic factor however immune system starts producing antibodies directed against the receptor mediating absorption of intrinsic factor-vitamin B12 complex.
Any of the above mentioned three conditions will ultimately lead to a net deficiency of vitamin B12, thus producing all the manifestations we see in the settings of pernicious anemia.