How are Ferritin and fatigue related?

Ferritin is an iron-storage protein and a key biomarker of the body's iron reserves. Low ferritin (iron deficiency) is a well-documented cause of fatigue, even in the absence of anemia – a condition called 'iron deficiency without anemia'. The mechanism is clear: iron is essential for hemoglobin synthesis and oxygen transport, but also for mitochondrial function and energy metabolism. Deficiency impairs cellular energy production. However, ferritin is also an acute-phase reactant; it can be elevated during inflammation, infection, or liver disease, masking a true iron deficiency. Conversely, very high ferritin (e.g., in hemochromatosis) can also cause fatigue. The evidence linking ferritin to fatigue is largely observational (human-moderate). Consumer lab tests measure ferritin reliably, but interpretation requires clinical context – a single value without additional markers (e.g., serum iron, transferrin saturation, CRP) can be misleading. Safety note: iron supplements should not be taken without confirmed deficiency, as overload is harmful.