Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Iron Deficiency

What Is It?

Iron deficiency is an abnormally low level of iron in the body.

Iron is an essential mineral found in red meat and certain fruits and vegetables. In the body, iron is needed to form myoglobin, a protein in muscle cells, and it is essential for certain enzymes that drive the body's chemical reactions. In the bone marrow, iron is used to make hemoglobin, the oxygen-carrying chemical inside the body's red blood cells. If iron levels fall too low, it causes iron deficiency anemia. When this happens, red blood cells become smaller than normal and contain less hemoglobin.

Iron deficiency can occur in infants, adolescents and pregnant women because of the heavy demands for iron associated with rapid body growth. Iron deficiency is especially common in premenopausal women because of regular loss of iron with menstrual periods.

Iron deficiency also can happen because of any of the following:

• An inadequate diet

• Poor absorption of iron resulting from the surgical removal of part or all of the stomach or intestine

• Inflammatory bowel disease

• An intestinal disorder called celiac sprue

• Chronic blood loss caused by any of the following:

  • Abnormally heavy menstrual periods

  • Bleeding into the urine, which is rare, or into the gastrointestinal tract, which is common; often, the blood loss is so small, it can only be detected with special testing

  • Excessive blood donation

  • A parasitic hookworm infestation