Common symptoms of iron-deficiency anemia include muscle weakness, shortness of breath, and lightheadedness. why does iron deficiency cause these symptoms? a. since iron is required for fluid balance, iron deficiency decreases the volume of blood that circulates in the body. b. since iron is required to make hemoglobin and myoglobin, iron deficiency decreases the amount of oxygen in the blood and in the muscles. c. since iron is required for fluid balance, iron deficiency increases the volume of blood that circulates in the body. d. since iron is required make hemoglobin and myoglobin, iron deficiency decreases the amount of carbon dioxide in the blood and in the muscles.