If there are not enough red cells or enough hemoglobin available, the lungs must work very hard to bring in more oxygen. Cause The body contains billions of red blood cells, but normally they live for only 120 days. As older, wornout red cells are destroyed, new cells are constantly being made in the bone marrow. Some anemias develop when not enough new red blood cells are produced to offset those that are wearing out. Still other anemias result from loss of blood.
Some women lose more blood than normal during their menstrual flow.
People who have an ulcer in the stomach or upper intestine may lose blood from internal bleeding. One of the greatest causes of anemia worldwide is hookworm infection. Several types of anemias are caused by a deficiency, or shortage, of a certain vitamin or mineral in the body. Iron is usually stored in the bone marrow, liver , or spleen until it is needed to produce new red blood cells. If more iron is lost or used up than that which the body takes in, or absorbs, iron-deficiency anemia develops.