Extrinsic iron from soil contributes to Hb regeneration of anaemic rats: implications for foods contaminated with soil iron

Contamination of foods with extrinsic (soil) Fe is common in developing countries. However, the bioavailability of this extrinsic Fe and the extent to which it contributes to Fe nutrition remains unknown. The present study compared the bioavailability of laboratory- and field-threshed teff (Eragrostisis tef (Zucc) Trotter) to evaluate the bioavailablity of extrinsic soil Fe that resulted from the traditional threshing of the staple grain. Using sequential extraction, Fe was fractionated and its solubility was evaluated. The contribution of the additional extrinsic (soil) Fe to the Hb regeneration of Fe-depleted rats was evaluated using a rat Hb depletion–repletion assay. Weanling male Wistar rats (n 24) were fed Fe-deficient diet for 21 d, and were then repleted for 14 d with diets: either laboratory-threshed teff (35 mg Fe/kg; n 8), field-threshed teff (35 mg intrinsic Fe/kg+ 120 mg soil Fe/kg; n 8), or FeSO₄ (control; n 8). Fe content of field-threshed teff (29·4 mg/100 g) was four times greater than that of the laboratory-threshed (6·7 mg/100 g) teff (P<0·05). Soil contamination significantly increased the exchangeable, acid-soluble and reducible fractions obtained after sequential extraction. The relative biological value of the field-threshed teff (88 %) was higher than that of the laboratory-threshed (68 %) teff (P<0·05). Soil Fe can contribute to Hb regeneration in Fe-deficient rats. Considering that contamination of foods with soil is common in Ethiopia and other developing countries, it needs to be accounted for in the design and implementation of fortification programmes to prevent excessive intakes. Human studies are needed to confirm the present findings.