Ferritin

Ferritin is a ubiquitous intracellular iron-storage protein that releases a small fraction into circulation; serum ferritin is therefore the most widely used biomarker for assessing total body iron stores. Low ferritin (typically <30 µg/L, or <15 µg/L in some guidelines) indicates depleted iron stores preceding overt iron-deficiency anemia and is associated with fatigue, reduced exercise capacity, impaired cognitive function, and hair loss even before hemoglobin falls. Conversely, elevated ferritin is a potent positive acute-phase reactant that rises substantially with inflammation, infection, liver disease, obesity, and metabolic syndrome, complicating interpretation; persistently elevated values without these confounders may reflect hereditary hemochromatosis or secondary iron overload, which accelerates oxidative stress, hepatic fibrosis, and cardiomyopathy. Optimal ferritin for health is debated; many longevity-oriented practitioners target approximately 70–120 µg/L, with caution warranted at both extremes.