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Letter to the Editor

The Effect of Na₂EDTA on Iron Absorption from Ferrous Fumarate

Laboratory for Human Nutrition, Institute of Food Science and Nutrition, Swiss Federal Institute of Technology Ruschlikon, Switzerland

Dear Editor:

Although the enhancing effect of Na₂EDTA on ferrous sulfate has been demonstrated in several human studies, for example by Davidsson et al. (1), there are limited data on the potentially enhancing effect of Na₂EDTA on nonwater soluble iron compounds. We recently investigated the effect of Na₂EDTA on iron absorption from ferrous fumarate in young Guatemalan girls and adult Swiss women (2,3), using a stable isotope technique. The data from both studies were conclusive; no enhancing effect of Na₂EDTA on iron absorption from ferrous fumarate was demonstrated.

We were therefore surprised by the recent publication by Walter et al. (4), reporting an enhancing effect of Na₂EDTA on iron absorption from corn masa tortillas fortified with ferrous fumarate in adult women. The discrepancy between the data presented by Walter et al. and our previous study in Guatemala (2) is assumed by Walter et al. to be attributed to differences in the preparation of test meals (iron fortified tortillas). However, we suggest that the difference in results is due to differences in the labeling technique, a more fundamental difference in study design. Walter et al. (4) have not discussed this important issue.

Our previous studies on the effect of Na₂EDTA on iron absorption from ferrous fumarate used intrinsically labeled ferrous fumarate (2,3). The labeled material was produced in collaboration with a manufacturer of commercial ferrous fumarate and has been demonstrated to have similar solubility properties as commercial ferrous fumarate (2). In contrast, Walter et al. prepared labeled test meals by adding unlabeled ferrous fumarate together with a water-soluble, extrinsic label (⁵⁹FeCl₃ or ⁵⁵FeCl₃) to the corn masa flour. Iron absorption was measured from the extrinsically labeled test meal with or without added Na₂EDTA. It should be noted that the validity of the extrinsic labeling technique for studies of iron absorption from nonwater soluble iron compounds has not been demonstrated. Due to differences in solubility properties, it is highly unlikely that the addition of a water-soluble iron compound, for example ferric chloride, can be used to evaluate iron absorption from a nonwater soluble iron compound such as ferrous fumarate. Iron ingested as FeCl₃ can be expected to enter the common nonheme iron pool rapidly while ferrous fumarate has to dissolve in the gastric juice before iron is released and available to enter the common nonheme iron pool. Thus, it can be expected that Na₂EDTA will form complexes more rapidly with iron provided as water-soluble compounds, for example as FeCl₃, or with other trace elements, than with iron from ferrous fumarate. The enhancing effect of Na₂EDTA on iron absorption from ferrous fumarate reported by Walter et al. can therefore be assumed to be an artifact, due to the inappropriate labeling technique used in the Chilean study.

Manuscript received 16 January 2004.

LITERATURE CITED

1. Davidsson, L., Walczyk, T., Zavaleta, N. & Hurrell, R. F. (2001) Improving iron absorption from a Peruvian school breakfast meal with ascorbic acid or Na₂EDTA. Am. J. Clin. Nutr. 73:283-287.[Abstract/Free Full Text]

2. Davidsson, L., Dimitriou, T., Boy, E., Walczyk, T. & Hurrell, R. F. (2002) Iron bioavailability from iron fortified Guatemalan meals based on corn tortillas and black bean paste. Am. J. Clin. Nutr. 75:535-539.[Abstract/Free Full Text]

3. Fidler, M. C., Davidsson, L., Zeder, C., Walczyk, T. & Hurrell, R. F. (2003) Iron absorption from ferrous fumarate in adult women is influenced by ascorbic acid but not by Na₂EDTA. Brit. J. Nutr. 90:1081-1085.[Medline]

4. Walter, T., Pizzaro, F. & Olivares, M. (2003) Iron bioavailability in corn-masa tortillas is improved by the addition of disodium EDTA. J. Nutr. 133:3158-3161.[Abstract/Free Full Text]

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