Iron is one of the human body's essential minerals. It forms part of hemoglobin, the component of the blood that carries oxygen throughout the body. People with iron-poor blood tyre easily because their bodies are starved for oxygen. Iron is also part of myoglobin, which helps muscles store oxygen. With insufficient iron, adenosine triphosphate (ATP; the fuel the body runs on) cannot be properly synthesized. As a result, some iron-deficient people can become fatigued even when they are not anemic.