Pernicious anemia is a disease in which the red blood cells are abnormally formed, due to an inability to absorb vitamin B₁₂. Vitamin B₁₂, or cobalamin, plays an important role in the development of red blood cells. It is found in significant quantities in liver, meats, milk and milk products, and legumes. During the course of the digestion of foods containing B₁₂, the B₁₂ becomes attached to a substance called intrinsic factor. Intrinsic factor is produced by parietal cells which line the stomach. The B₁₂-intrinsic factor complex then enters the intestine, where the vitamin is absorbed into the bloodstream. In fact, B₁₂ can only be absorbed when it is attached to intrinsic factor.

In pernicious anemia, the parietal cells stop producing intrinsic factor. The intestine is then completely unable to absorb B₁₂. So, the vitamin passes out of the body as waste. Although the body...