In vitro studies suggest inhibitory interactions may occur between iron and zinc in rice fortified with a premix approach, where a fraction of the grains (typically 1:100) is enriched with high micronutrient concentrations.We investigated whether zinc added as oxide (ZnO) or sulfate (ZnSO4) influences fractional iron absorption (FAFe) from ferric pyrophosphate fortified extruded rice.
We conducted an iron absorption study in young iron-deficient women (n=19) (plasma ferritin <16.5µg/l) comparing four different rice meals, each containing 4mg iron. Three were fortified with labeled FePP (57FePP): 1) one without added Zn (Fe-Zn); 2) one cofortified with ZnO (Fe+ZnO); and 3) one cofortified with ZnSO4 (Fe+ZnSO4); and a fourth reference meal of non-fortified extruded rice with ferrous-sulfate (58FeSO4) added to the meal after cooking. Iron absorption was measured as erythrocyte incorporation of stable iron isotopes 14 days after meal-administration.
Geometric mean FAFe (-SD,+SD) was higher from Fe+ZnSO4: 4.5% (2.5, 8.1%) compared to Fe+ZnO: 2.7% (1.1, 6.8%) (P<.03) and both did not differ significantly from Fe-Zn: 4.0% (1.9, 8.6%). Relative bioavailability compared to FeSO4 was 48%, 43% and 29% from Fe+ZnSO4, Fe-Zn and Fe+ZnO, respectively.
Iron absorption from FePP-fortified extruded rice was 40% lower when co-fortified with ZnO but not significantly affected when cofortified with ZnSO4. Future research should determine if this interaction occurs in other fortified foods.