How are Ferritin Eisenmangel and fatigue related?

Ferritin is the body's iron storage protein. Low ferritin (iron deficiency) is a well-established cause of fatigue, even before anemia develops, because iron is critical for mitochondrial energy production and oxygen transport. Clinical studies show that iron supplementation reduces fatigue in individuals with ferritin below 30 µg/L, regardless of hemoglobin levels. However, fatigue is multifactorial—sleep, stress, thyroid function, and other deficiencies can contribute. A ferritin test can help, but results must be interpreted with caution: ferritin is an acute-phase reactant, so inflammation can falsely elevate or normalize levels. Evidence is moderate (human studies, but not from the provided context).