Iron - is an essential mineral that, among other things, is part of hemoglobin--the oxygen carrying component of the blood. Iron deficiency is characterized by chronic fatigue. Iron is also needed to create ATP--the molecule used by our cells for energy--so even non-anemic individuals can become fatigued if they are low on iron. Over-supplementation of iron is harmful, especially in children. Iron is found in oysters, meat, poultry, fish, leafy green vegetables and molasses.