Smaller iron particle size improves bioavailability of hydrogen-reduced iron–fortified bread

Bioavailability results, obtained in humans, of wheat flour fortified with elemental iron might not be reliable because these studies have been performed using tracer iron compounds that probably do not have the same physicochemical characteristics as the commercial elemental iron powders. The aim of the present study was to measure, in Caco-2 cells, the iron bioavailability of hydrogen-reduced (H-reduced) iron (≤45-μm particle size) from 72%-extraction wheat flour bread. Bread was fortified with either 8-μm H-reduced iron (pro analysi compound used as control) or ≤45-μm H-reduced iron (industrialized food grade product). Solubility and dialyzability were determined from bread homogenate. Ferritin and intracellular iron content were assessed in Caco-2 cells incubated with either reduced iron or fortified bread homogenate. The 8-μm H-reduced iron had higher solubility and dialyzability than ≤45-μm H-reduced iron. Intracellular iron and ferritin concentrations in Caco-2 cells exposed to digest from bread fortified with 8-μm H-reduced iron were significantly higher than in bread fortified with ≤45-μm H-reduced iron (P < .05). When bread fortified with ferrous sulfate was used as a reference, the relative iron bioavailabilities of the fortified bread with 8-μm H-reduced iron and ≤45-μm H-reduced iron were 68.2% and 31.1%, respectively. In conclusion, there is an inverse relationship between H-reduced particle size and iron bioavailability. If H-reduced (food grade, ≤45-μm particle size) iron is used in wheat flour fortification, it should be added at 3 times the level of ferrous sulfate to provide the same absolute amount of absorbed iron.