Nonanemic Iron Deficiency: Exercise Performance Recovery After Iron Repletion in Collegiate Athlete.

backgroundExercise intolerance in athletes is often attributed to cardiopulmonary or autonomic causes; however, nonanemic iron deficiency is a common and under-recognized contributor that may hinder aerobic adaptation. Ferritin thresholds used in general populations do not reflect athletes' higher physiological iron requirements. CASE SUMMARY: A 21-year-old collegiate gymnast presented with exertional intolerance, positional lightheadedness, and tachycardia. Cardiopulmonary exercise testing showed reduced aerobic capacity (peak oxygen consumption: 25.5 mL/kg/min; 67% predicted). Iron studies revealed marked deficiency (ferritin: 15 μg/L, transferrin saturation: 13%) despite normal hemoglobin (14.1 g/dL). She was treated with intravenous iron; 5 months later, iron normalized, symptoms improved, and peak oxygen consumption increased to 31.2 mL/kg/min (81% predicted). DISCUSSION: This case highlights that nonanemic iron deficiency can mimic deconditioning and dysautonomia yet is fully reversible when identified early. Physiological evidence supports using ferritin <50 μg/L to detect clinically relevant deficiency in athletes. TAKE-HOME MESSAGES: Iron deficiency without anemia should be considered early in athletes with unexplained exercise intolerance.