Davis 2024, Comment on Šmid et al. iron supplementation meta-analysis

Methodological letter in Sports Medicine responding to Šmid et al. 2024. Davis argues that serum ferritin is a continuous physiological variable, so splitting athletes at a single cutoff (≤12 vs >12 µg/L) to show that supplementation only helps the deficient discards information and oversimplifies the picture: the benefit of iron supplementation declines continuously as baseline ferritin rises, rather than switching off at a threshold. The original authors, in their reply, accepted that ferritin is continuous but defended dichotomised cutoffs as standard clinical practice, maintaining that the substantive conclusion is unchanged — the lower the baseline ferritin, the greater the benefit.