The bulk of the iron in the human body is in the red blood cells' hemoglobin; in fact, it is what makes blood red. Hemoglobin shuttles oxygen from the lungs to every body cell, and without iron, hemoglobin cannot do its job. Another compound, myoglobin, grabs iron from hemoglobin and stores it in muscles where it's crucial to proper muscle function. On hemoglobin's trip to the lungs, its iron carries carbon dioxide, which we then expel as we exhale. And that's not all. Iron is part of the chemical makeup of several vital enzymes and proteins and plays a major role in energy metabolism.