Low ferritin can cause fatigue, and this is one of the most common complaints. When iron stores fall, energy production, muscle performance, and cognitive efficiency can all be affected indirectly. A person may feel weak, mentally slower, less motivated, or exhausted more quickly during the day. In some individuals, this can happen even before hemoglobin becomes abnormal. That is why the idea that “fatigue only happens when there is anemia” is incomplete. Of course, ferritin is not the only possible cause of fatigue; sleep problems, thyroid disorders, stress, depression, vitamin deficiencies, and chronic illnesses can create a similar pattern. Still, when fatigue is persistent, ferritin is one of the key markers worth evaluating.