This can happen after sudden bleeding due to an accident, surgery, childbirth, or a ruptured blood vessel. It can also develop more gradually as a result of chronic nosebleeds, heavy menstrual cycles, hemorrhoids, stomach or small intestinal ulcers, kidney or bladder tumors, or gastrointestinal cancer. A variety of mechanisms underlie the other major types of anemia. Depletion of the body's stores of iron is usually a result of chronic, hidden bleeding. The lack of a chemical called intrinsic factor renders the body unable to absorb the vitamin B 12 needed to produce red blood cells.
Intrinsic factor is manufactured in the lining of the stomach.
Supplies can be disrupted by certain parasites, inflammatory bowel disease, and diseases of the small intestine. Disorders such as thyroiditis and diabetes can also be at fault. Alcoholism is another potential culprit. Anything that harms bone marrow can lead to a decline in blood cell production. Immunosuppressive drugs, anticancer drugs, and other toxic chemicals bring on many cases in this category.