Iron Bioavailability from Ferric Pyrophosphate in Extruded Rice Cofortified with Zinc Sulfate Is Greater than When Cofortified with Zinc Oxide in a Human Stable Isotope Study

Extruded rice grains are often cofortified with iron and zinc. However, it is uncertain if the addition of zinc to iron-fortified rice affects iron absorption and whether this is zinc-compound specific. We investigated whether zinc, added as zinc oxide (ZnO) or zinc sulfate (ZnSO ), affects human iron absorption from extruded rice fortified with ferric pyrophosphate (FePP). In 19 iron-depleted Swiss women (plasma ferritin ≤16.5 μ/L) aged between 20 and 39 y with a normal body mass index (in kg/m ; 18.7-24.8), we compared iron absorption from 4 meals containing fortified extruded rice with 4 mg Fe and 3 mg Zn. Three of the meals contained extruded rice labeled with FePP ( FePP): ) 1 meal without added zinc ( FePP-Zn), ) 1 cofortified with ZnO ( FePP+ZnO), and ) 1 cofortified with ZnSO ( FePP+ZnSO ). The fourth meal contained extruded rice without iron or zinc, extrinsically labeled with ferrous sulfate ( FeSO ) added as a solution after cooking. All 4 meals contained citric acid. Iron bioavailability was measured by isotopic iron ratios in red blood cells. We also measured relative in vitro iron solubility from FePP-Zn, FePP+ZnO, and FePP+ZnSO expressed as a fraction of FeSO solubility. Geometric mean fractional iron absorption (95% CI) from FePP+ZnSO was 4.5% (3.4%, 5.8%) and differed from FePP+ZnO (2.7%; 1.8%, 4.1%) ( < 0.03); both did not differ from FePP-Zn: 4.0% (2.8%, 5.6%). Relative iron bioavailabilities compared with FeSO were 62%, 57%, and 38% from FePP+ZnSO , FePP-Zn, and FePP+ZnO, respectively. In vitro solubility from FePP+ZnSO differed from that of FePP-Zn (14.3%; < 0.02) but not from that of FePP+ZnO (10.2% compared with 13.1%; = 0.08). In iron-depleted women, iron absorption from FePP-fortified extruded rice cofortified with ZnSO was 1.6-fold (95% CI: 1.4-, 1.9-fold) that of rice cofortified with ZnO. These findings suggest that ZnSO may be the preferable zinc cofortificant for optimal iron bioavailability of iron-fortified extruded rice. This trial was registered at clinicaltrials.gov as NCT02255942.