What Causes Pernicious Anemia?

Major Causes

Pernicious anemia is caused by a lack of vitamin B12 in the body. The main reason for the vitamin B12 deficiency is the loss of parietal (pa-RI-e-tal) cells in the lining of the stomach. These cells make intrinsic factor, which helps the body absorb vitamin B12 in the small intestine. In some people, the body’s immune system may attack and destroy the parietal cells. Doctors don’t know exactly why or how this happens, or if the immune system produces antibodies in reaction to normally aging or dying parietal cells.

As a result of this immune system attack, the stomach lining shrinks, and the parietal cells in the lining of the stomach disappear. The stomach stops producing intrinsic factor. Over time, vitamin B12 deficiency develops.

Loss of intrinsic factor can also be due to removal of the stomach lining in various kinds of stomach surgery. This surgery includes removal of all or part of the stomach as well as stomach surgery for weight loss.

There is also a rare inherited disorder in which children are born without the ability to produce intrinsic factor.

Other Causes

Less common causes of pernicious anemia include a diet low in vitamin B12, intestinal problems, and certain medicines.

Lack of Vitamin B12 in the Diet

People can develop pernicious anemia if they don’t get enough vitamin B12 in the foods that they eat. This condition takes many years to develop because it takes time to use up the vitamin B12 already stored in the body.

Some people who are strict vegetarians can develop pernicious anemia, especially if they do not eat meat, poultry, fish, eggs, or dairy products––the best food sources of vitamin B12. Breastfed infants of strict vegetarian mothers can develop anemia in a short time because they don’t have enough vitamin B12 stored in their bodies. They can be given vitamin B12 supplements to prevent this type of anemia.

Some people develop pernicious anemia because of a poor diet due to conditions such as alcoholism or aging.

Disorders of the Small Intestine

Some intestinal problems can cause poor absorption of vitamin B12. These problems include:

• An infection caused by parasites or an overgrowth of bacteria in the intestine
• Celiac disease (also known as sprue), a genetic disorder that makes a person unable to tolerate gluten
• Crohn’s disease, an inflammatory bowel disease
• Not enough stomach acid to digest food—a problem that can occur in older adults

Medicines

Long-term use of certain medicines may lead to pernicious anemia. Examples of these are medicines that reduce acid in the stomach and certain diabetes medicines (such as metformin, phenformin, and biguanides).