Intrinsic factor is a protein that helps your intestines absorb vitamin B12. It is made by cells in the stomach lining.
Intrinsic factor binds to vitamin B12. After attaching, intrinsic factor and B12 travel to the intestines to be absorbed into the bloodstream. Vitamin B12 is needed for red blood cells to form and grow.
Some people do not make enough intrinsic factor or have a condition that destroys it. If your body does not make enough intrinsic factor, you can develop a type of vitamin B12 deficiency called pernicious anemia.
Surgical removal or bypass of the stomach and certain other health conditions can also cause you to stop making intrinsic factor.
Antony AC. Megaloblastic anemias. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 7th ed. Philadelphia, PA: Elsevier; 2018:chap 39.