Intrinsic factor is a protein produced by cells in the stomach lining. It is needed for the intestines to absorb vitamin B12 efficiently.
In a disease called pernicious anemia, immune system damage to the stomach lining can cause a lack (deficiency) of intrinsic factor. Pernicious anemia causes vitamin B12 deficiency, which leads to a low red blood cell count (anemia).
Intrinsic factor deficiencies can also be caused by other reasons, such as: