Definition

A condition in which the body is unable to properly absorb vitamin B12, leading to a lower-than-normal number of red blood cells in the body. Vitamin B12 binds to a protein in the stomach called intrinsic factor. This allows vitamin B12 to be absorbed in the small intestine and then released into the bloodstream. Pernicious anemia occurs when there is too little intrinsic factor to bind enough vitamin B12 for it to be used by the body to make red blood cells. In most cases, this happens when the body’s immune system attacks the intrinsic factor protein or the cells in the lining of the stomach that make it. It may also occur in people with atrophic gastritis, a condition marked by chronic inflammation and thinning of the inner lining of the stomach. If not treated, pernicious anemia can lead to serious problems, including damage to the nervous system. People with pernicious anemia may have an increased risk of stomach cancer, gastrointestinal neuroendocrine tumors, or some other types of cancer.