Pernicious anemia is caused by an inability to absorb vitamin B12 (cobalamin) that is naturally found in certain foods. These foods are all of animal origin and include meat, milk and dairy products, and eggs. Vitamin B12 is not found in plants. Although bacteria in the large intestine produce vitamin B12, it is not absorbed into the blood stream from this site. Most people need only 2 micrograms of vitamin B12 daily but the average diet provides about 5 to 30 micrograms a day.
When it is ingested, vitamin B12 needs to be chemically linked to a substance called intrinsic factor, which is produced in the stomach. In the animation on the right, vitamin B12 is shown in pink and the intrinsic factor is shown in blue. They combine in the stomach and pass into the small intestine where the intrinsic factor helps the vitamin B12 get absorbed into the circulation. Through the circulation, the vitamin is transported to the liver where it is stored, being released back into the circulation as needed. Without intrinsic factor, vitamin B12 is not absorbed and pernicious anemia occurs.
Other causes of vitamin B12 deficiency produce the same symptoms as pernicious anemia. Diseases of the small intestine that cause malabsorption may cause vitamin B12 deficiency. Vegans (individuals who consume absolutely no foods of animal origin) are at risk of vitamin B12 deficiency due insufficiency of this vitamin in their diet. But it takes a long time to deplete all the vitamin B12 that is stored in the liver. Even if the absorption of vitamin B12 is suddenly cut off (for example, as in gastrectomy, surgical removal of the stomach), there is enough vitamin B12 stored in the liver to last for one to five years.
Lack of vitamin B12 produces megaloblastic anemia, nerve damage, soreness of the tongue, and mental changes. Megaloblastic anemia is due to a defect that develops in the formation of blood cells. In the picture on the left, the relative sizes of the normal and abnormal red blood cells are shown as seen through a microscope. Red blood cells are normally formed in the bone marrow from larger cells that gradully shrink so that they are able to pass through the smallest blood vessels. Vitamin B12 helps in this shrinking process. Without vitamin B12, there are insufficient numbers of red blood cells, and those that are in the circulation are large and quickly become damaged. This leads to anemia, meaning that there is a deficiency of normal red blood cells. Nerve damage occurs in the hands and feet and leads to a feeling of pins and needles, and numbness. The tissue in the spinal cord that carries nerve impulses of touch and other sensations also is damaged, a condition called subacute combined degeneration of the spinal cord. The animation on the right shows nerve impulses from the legs getting weaker as they go up the spinal cord.
Laboratory tests for pernicious anemia may include
Note: The material provided in this web page is educational in nature and not medical advice. It is meant neither for self-diagnosis nor as a treatment recommendation. If you are concerned about any condition you think you may have, CONSULT YOUR DOCTOR.