Absorption of zinc from wheat products fortified with iron and either zinc sulfate or zinc oxide

Background: Several chemical forms of zinc have been proposed for food fortification, but information is needed on their absorption from common cereals having varied phytate content. Objective: The goal was to measure zinc absorption from wheat products fortified with iron sulfate and either zinc sulfate or zinc oxide. Design: Adult volunteers received either low-phytate bread (n = 11) or higher-phytate porridge (n = 11) once weekly on 2 or 3 occasions. The foods were fortified with 1 of the 2 zinc salts (60 mg elemental Zn/kg wheat flour) during week 1 and with the other during week 2, in random order. Zn-65 in the same chemical form as the fortificant was incorporated in each food to assess zinc absorption with the use of whole-body counting. The porridge group received an additional test meal fortified with zinc oxide during week 3, but the Zn-65 tracer was given as an oral solution of (ZnCl2)-Zn-65. Results: Zinc absorption from bread (13.8%; 95% CI: 11.8%, 16.2%) was significantly (P < 0.001) greater than from porridge (6.4%; 5.5%, 7.6%), presumably because of the greater phytate content of the porridge. With control for food type, there were no significant differences in zinc absorption from meals fortified with zinc sulfate or zinc oxide (P = 0.24). When the porridge was fortified with zinc oxide and labeled with (ZnCl2)-Zn-65, absorption of the tracer (8.9%; 7.1%, 11.0%) was significantly (P = 0.007) greater than when (ZnO)-Zn-65 was incorporated in the porridge (5.6%; 4.5%, 6.9%). Conclusions: Either zinc oxide or zinc sulfate can be used to fortify wheat products consumed by presumably healthy persons. Isotopic tracers used to assess the absorption of mineral fortificants should have the same chemical form as the fortificant.