What role does Ferritin play in fatigue?

Ferritin is the body's primary iron storage protein. Low ferritin indicates depleted iron stores, which can cause fatigue even without anemia. Strong evidence shows that ferritin levels below 30 µg/L are associated with tiredness, reduced exercise capacity, and cognitive fog. Iron deficiency impairs oxygen transport and mitochondrial function, directly affecting energy production. Causes include blood loss, poor intake, or malabsorption. Conversely, elevated ferritin may reflect inflammation, hemochromatosis, or liver disease, all of which can also present with fatigue. Interpretation requires context: CRP, transferrin saturation, and hemoglobin. Home blood tests can measure ferritin, but clinical correlation is crucial. For persistent fatigue, checking ferritin is a reasonable first step, but it should not be interpreted in isolation. Evidence level: human-strong for low ferritin and fatigue; moderate for high ferritin.