Pernicious anemia is caused by 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. It helps your body absorb vitamin B12. In some people, an autoimmune response causes a lack of intrinsic factor.
                
An autoimmune response occurs if the bodys 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-eh-tal) cells. These cells line the stomach and 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 surgically 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
                
Pernicious anemia also has other causes, besides a lack of intrinsic factor. Malabsorption in the small intestine and a diet lacking vitamin B12 both can lead to pernicious anemia.
                
Malabsorption in the Small Intestine
                
Sometimes pernicious anemia 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, an inflammatory bowel disease. HIV also may interfere with vitamin B12 absorption.
                
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 of the vitamin B12. Eating undercooked, infected fish may cause this type of infection.
                
Diet Lacking Vitamin B12
                
Some people get pernicious anemia because they don't have enough vitamin B12 in their diets. This cause of pernicious anemia is less common than other causes.
                
Good food sources of vitamin B12 include:
                
Breakfast cereals with added vitamin B12
                
Meats such as beef, liver, poultry, and fish
                
Eggs and dairy products (such as milk, yogurt, and cheese)
                
Foods fortified with vitamin B12, such as soy-based beverages and vegetarian burgers
                
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. These people may not get the proper nutrients in their diets.