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Increased iron loss may reduce the effectiveness of iron supplementation. The objective of this study was to determine if daily oral iron supplementation increases iron loss, measured using a stable isotope of iron (58 Fe). We enrolled and dewormed 24 iron-depleted Kenyan children, 24-27 months of age, whose body iron was enriched and equilibrated with 58 Fe given at least 1 year earlier. Over 3 months of supplementation (6 mg iron/kg body weight [BW]/day), mean (±SD) iron absorption was 1.10 (±0.28) mg/day. During supplementation, 0.55 (±0.36) mg iron/day was lost, equal to half of the amount of absorbed iron. Supplementation did not increase faecal haem/porphyrin or biomarkers of enterocyte damage and gut or systemic inflammation. Using individual patient data, we examined iron dose, absorption and loss among all available long-term iron isotopic studies of supplementation. Expressed in terms of body weight, daily iron loss was correlated significantly with iron absorption (Pearson's r = 0.66 [95% confidence interval 0.48-0.78]) but not with iron dose (r = 0.16 [95% CI -0.10-0.40]). The results of this study indicate that iron loss is increased with daily oral iron supplementation and may blunt the efficacy of iron supplements in children. This study was registered at as NCT04721964.

Original publication




Journal article


Br J Haematol

Publication Date



iron absorption, iron deficiency, iron losses, iron supplementation, stable iron isotope