Anemia is a condition that develops when your blood lacks enough healthy red blood cells or hemoglobin. Hemoglobin (Iron is an essential component of hemoglobin) is a main part of red blood cells which binds oxygen. If you have too few or abnormal red blood cells or hemoglobin, the cells in your body can not get enough oxygen. Symptoms of anemia -- like fatigue and lower body immunity -- occur because organs aren't getting what they need to function properly. There are many types of anemia. All are very different in their causes and treatments. Iron deficiency anemia, the most common type, is very treatable with iron supplements.