Iron is an essential mineral necessary for the transport of oxygen throughout the body. It is carried by red blood cells and transports oxygen from your lungs to all the tissues of your body. Iron deficiency anemia occurs when there is a lack of iron in your red blood cells, leading to inadequate transport of oxygen to your tissues and organs. Iron deficiency anemia is one of the most common causes of fatigue. Symptoms of Iron Deficiency Include: Weakness and fatigue Headache