Extreme fatigue
Extreme tiredness is the most prominent symptom of low iron levels in the body. The tiredness sufferers experience is the result of oxygen deprivation in the muscles and tissues. The blood requires iron to make hemoglobin which then delivers oxygen to these tissues.
When there is no iron to make hemoglobin, the tissues do not get sufficient oxygen and are not able to muster the energy to function well. The resulting shortage of oxygen also increases the work your heart does to transport well-oxygenated blood around the body. All of this contributes to the fatigue experienced when the body is low on iron.
The tiredness caused by iron deficiency is often quite profound but is not enough to reach a conclusive diagnosis of iron deficiency.