Iron is one of the most abundant metals in the universe. It is also one of the most useful in biochemical functions. In the human body, iron is present in all cells and has several vital functions — as a carrier of oxygen to the tissues from the lungs in the form of hemoglobin, as a facilitator of oxygen use and storage in the muscles as myoglobin, as a transport medium for electrons within the cells in the form of cytochromes, and as an integral part of enzyme reactions in various tissues. Adequate iron stores support energy production, hormones, and neurological health. Low iron levels in the blood are the most common and most prevalent mineral deficiency in the world. A diminished supply of iron can result in a decreased concentration of red blood cells and a diminished delivery of oxygen to tissues which may result in irritability, inability to concentrate, and low immune function. Common causes of low iron include gastrointestinal malabsorption, pregnancy or menstruation, inadequate iron intake from the diet mostly seen in vegetarians, consumption of foods that inhibit iron absorption, and intense exercise.