In the stomach, a protein called intrinsic factor binds vitamin B12. After attaching, it travels to the small intestine where it can be absorbed into your blood. A lack of intrinsic factor can cause a type of anemia known as pernicious anemia.
It occurs when abnormal antibodies, produced by the body's immune system, attack and destroy the stomach cells that make intrinsic factor. This happens in an autoimmune reaction called autoimmune metaplastic atrophic gastritis. In rare cases, an inherited disorder prevents the body from making intrinsic factor.
Some diseases and medical treatments can also cause a lack of intrinsic factor. These include alcoholism, H. pylori infection, and surgery to remove or bypass part of the stomach.
These disorders damage the parietal (pa-RI-eh-tal) cells that line the stomach and make intrinsic factor. These cells produce a protein that helps the stomach and small intestine absorb dietary vitamin B12.
Intrinsic factor is made by these parietal cells in response to the nutrients in food. When the stomach is damaged, such as by alcoholism or ulcerative gastritis, the parietal cells die and intrinsic factor is not made.
Without the ability to absorb vitamin B12, red blood cells cannot form and grow. This leads to a type of anemia known as pernicious or megaloblastic anemia. It can be caused by a lack of intrinsic factor or other conditions, such as a malabsorption of vitamin B12 in the small intestine or a diet that does not contain enough dietary vitamin B12.