People with anemia, regardless of cause, feel dragged out because the diminished population of red blood cells cannot supply the body with the oxygen it needs. Red blood cells are trucks that transport oxygen from the lungs to all body organs and tissues. Iron deficiency is a common cause of anemia. If that is the case, the next step is finding the reason for the iron deficiency. Bleeding is often the cause of iron-deficiency anemia.
Blood is the largest depository for iron.
The bleeding can be internal and not obvious to the patient. However, there are many other reasons why anemias develop. One is a deficiency of vitamin B-12. The resulting anemia is called pernicious anemia. Another anemia cause is bone marrow failure.