B12 is found in meat and dairy, so other than vegans most people should get enough.
Absorption of B12 is specific; it requires intrinsic factor (which is released from parietal cells in the stomach) to bind to it and it is then absorbed as a complex uniquely in the terminal ileum.
Deficiency of B12 causes a variety of symptoms and signs:
- peripheral neuropathy
- subacute combined degeneration of the spinal cord
Investigations will show a macrocytic anaemia, and in severe cases WCC and platelets may also be decreased.
Causes of B12 deficiency can be split into:
- insufficient intake
- lack of absorption
- lack of intrinsic factor
- pernicious anaemia (see next battle)
- lack of terminal ileum/absorption space
- fish tapeworm, Diphyllobothrium
- drugs interfering with absorption, eg metformin
Treatment is to treat the cause/give B12.
Lets have a quick look at pernicious anaemia...