Hepcidin can throttle iron absorption after a daily dose, which may be why oral iron so often disappoints and upsets the stomach. A 2026 randomized trial in 66 iron-deficient women tested 21 mg of iron every 48 hours against 30 mg daily for 42 days. Ferritin rose significantly in both groups with no significant difference between them, while hemoglobin stayed stable and GI effects were mild. The catch is that this was active-controlled with no placebo, and the iron forms differed, so the result is comparable rather than superior. Here is what it means for women who train, and why you should test ferritin before supplementing.
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