Pernicious anemia (PA) is a decrease in red blood cells that occurs when the intestines cannot properly absorb vitamin B12. Red blood cells provide oxygen to body tissues. There are many types of anemia. Pernicious anemia is a type of vitamin B12 anemia. The body needs vitamin B12 to make red blood cells. You get this vitamin from eating foods such as meat, poultry, shellfish, eggs, and dairy products. A special protein, called intrinsic factor (IF), helps your intestines absorb vitamin B12. This protein is released by cells in the stomach. When the stomach does not make enough intrinsic factor, the intestine cannot properly absorb vitamin B12. Common causes of pernicious anemia include: weakened stomach lining (atrophic gastritis), an autoimmune condition in which the body’s immune system attacks the actual intrinsic factor protein or the cells in the lining of your stomach that make it. Very rarely, pernicious anemia is passed down through families. This is called congenital pernicious anemia. Babies with this type of anemia do not make enough intrinsic factor. Or they cannot properly absorb vitamin B12 in the small intestine. In adults, symptoms of pernicious anemia are usually not seen until after age 30. The average age of diagnosis is age 60. Patients usually do well with treatment. It is important to start treatment early. Nerve damage can be permanent if treatment does not start within 6 months of symptoms.