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Iron supplements inhibit zinc but not copper absorption in vivo in ileostomy subjects^1,2,3

¹ From the Department of Human Biology, NUTRIM, Maastricht University, Maastricht, Netherlands (FJT and WHMS); the Department of Gastroenterology, NUTRIM, University Hospital Maastricht, Maastricht, Netherlands (R-JMB); and the Institute of Food Research, Norwich, United Kingdom (JRD, JAH, and VJB).

Background: Iron supplements may inhibit intestinal zinc and copper uptake because these elements may compete for binding to a transporter molecule (divalent metal transporter 1) that is located on the apical side of the small intestinal epithelium.

Objective: We quantified the interaction between different amounts of administered iron and the absorption of zinc and copper in humans.

Design: Eleven subjects with an ileostomy [mean (± SD) age: 55 ± 9 y] ingested a stable-isotope-labeled zinc and copper solution containing 12 mg Zn (⁶⁶Zn and ⁶⁷Zn) and 3 mg Cu (⁶⁵Cu) in the presence of 0, 100, or 400 mg Fe as ferrous gluconate on 3 respective test days. Subsequently, 1 mg ⁷⁰Zn was injected intravenously. Subjects collected ileostomy effluent and urine for 24 h and 7 d, respectively. Zinc status and true zinc absorption were calculated from the urinary excretion of the zinc isotopes. Apparent copper absorption was calculated from ileostomy effluent excretion of the orally administered copper isotopes.

Results: Zinc status did not differ significantly between the 3 iron doses. Mean (± SEM) zinc absorption was significantly higher in the absence of iron than with the concomitant ingestion of 100 or 400 mg Fe (44 ± 22% compared with 26 ± 14% and 23 ± 6%, respectively; P < 0.05), whereas zinc absorption did not differ significantly between the 100- and 400-mg Fe doses. Apparent copper absorption was 48 ± 14%, 54 ± 26%, and 53 ± 7% in the presence of 0, 100, and 400 mg Fe, respectively, and did not differ significantly between the 3 iron doses.

Conclusion: Oral iron therapy may impair zinc absorption and thus zinc status in a dose-independent fashion but does not affect copper absorption.

Key Words: Ileostomy • zinc • copper • iron • zinc absorption • copper absorption • small intestine

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