Anemia occurs when you have a level of red blood cells (RBCs) in your blood that is lower than normal. Iron deficiency anemia is the most common type of anemia, and it occurs when your body doesn’t have enough of the mineral iron. Your body needs iron to make a protein called hemoglobin. This protein is responsible for carrying oxygen to your body’s tissues, which is essential for your tissues and muscles to function effectively. When there isn’t enough iron in your blood stream, the rest of your body can’t get the amount of oxygen it needs. In women of childbearing age, the most common cause of iron deficiency anemia is a loss of iron in the blood due to heavy menstruation or pregnancy. A poor diet or certain intestinal diseases that affect how the body absorbs iron can also cause iron deficiency anemia. Doctors normally treat the condition with iron supplements or changes to diet.