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.

© 2017 American Society for Nutrition.