Iron is an essential trace mineral. Approximately 70% of the body's iron forms part of hemoglobin, a protein found in red blood cells. As part of hemoglobin, iron helps transport oxygen to all the tissues and cells in the body. The remainder of iron is found in myoglobin, a protein that supplies oxygen to the muscles. It also forms part of various enzymes and immune system compounds. Iron transports oxygen to all tissues and helps cells to respire, processes essential for life.