What Causes Pernicious Anemia?

Pernicious anemia is due to a lack of intrinsic factor or other causes, such as infections, surgery, medicines, or diet.

Lack of Intrinsic Factor

Intrinsic factor is a protein made in the stomach that helps your body absorb vitamin B12. In some people, lack of intrinsic factor is due to an autoimmune response.

An autoimmune response occurs when the immune system makes antibodies (proteins) that mistakenly attack and damage the body's tissues or cells.

In pernicious anemia, the body makes antibodies that attack and destroy the parietal (pa-RI-e-tal) cells. These are the cells in the lining of the stomach that make intrinsic factor. Why this autoimmune response occurs isn't known.

As a result of this attack, the stomach stops making intrinsic factor. Without intrinsic factor, your body can't move vitamin B12 through the small intestine, where it's absorbed. This leads to vitamin B12 deficiency.

A lack of intrinsic factor also can occur if you've had part or all of your stomach removed. This type of surgery reduces the number of parietal cells available to make intrinsic factor.

Rarely, children are born with an inherited disorder that prevents their bodies from making intrinsic factor. This disorder is called congenital pernicious anemia.

Other Causes

Besides a lack of intrinsic factor, other conditions and factors also can cause pernicious anemia.

Malabsorption in the Small Intestine

Sometimes pernicious occurs because the body's small intestine can't properly absorb vitamin B12. This may be the result of:

• Too many of the wrong kind of bacteria in the small intestine. This is a common cause of pernicious anemia in older adults. The bacteria use up the available vitamin B12 before the small intestine can absorb it.
• Diseases that interfere with vitamin B12 absorption. One example is celiac disease. This is a genetic disorder in which your body can't tolerate a protein called gluten. Another example is Crohn's disease. This is an inflammatory bowel disease.
• Certain medicines that alter bacterial growth or prevent the small intestine from properly absorbing vitamin B12. Examples include antibiotics and certain diabetes and seizure medicines.
• Surgical removal of part or all of the small intestine.
• A tapeworm infection. The tapeworm feeds off the vitamin B12. Eating undercooked, infected fish may cause this type of infection.

Diet

Less often, people develop pernicious anemia because they don't get enough vitamin B12 in their diets. The best food sources for vitamin B12 are meat, poultry, fish, eggs, and dairy products. You also can get vitamin B12 from dietary supplements.

Strict vegetarians who don't eat any animal or dairy products and don't take a vitamin B12 supplement are at risk for pernicious anemia.

Breastfed infants of strict vegetarian mothers also are at risk for pernicious anemia. These infants can develop anemia within months of being born. This is because they haven't had enough time to store vitamin B12 in their bodies. Doctors treat these infants with vitamin B12 supplements.

Other groups, such as the elderly and people who suffer from alcoholism, also may be at risk for pernicious anemia because they may not get the proper nutrients in their diets.