Bioavailability of zinc oxide added to corn tortilla is similar to that of zinc sulfate and is not affected by simultaneous addition of iron.
Rosado JL, Díaz M, Muñoz E, Westcott JL, González KE, Krebs NF, Caamaño MC, Hambidge M. Bioavailability of zinc oxide added to corn tortilla is similar to that of zinc sulfate and is not affected by simultaneous addition of iron. Food Nutr Bull. 2012 Dec; 33(4):261-6.