Comparison of bioavailability and transporters gene expression of four iron fortificants added to infant cereals

Iron deficiency is one of the most important nutritional disorders around the world. To reduce this health problem in infants, most countries have developed different iron fortification programs as a long-term strategy. However, it is necessary to select the best iron source to get the highest bioavailability with the lowest impact on the organoleptic properties of the foods. The aim of this research was to assess the in vitro bioavailability and intestinal cellular transport of four iron sources (electrolytic iron: EI, ferrous fumarate: FF, a micronized and dispersible ferric pyrophosphate: MDFP, and ferrous sulphate heptahydrated: FSH) used to fortify infant cereals. Fortified cereals were in vitro digested and soluble fractions were then incubated in Caco-2 cells to study iron retention, transport and uptake. Moreover, mRNA expression of iron transporters and ferritin formation were also measured in cells incubated with the iron standard salts. Iron solubility, uptake percentage, transport and uptake efficiencies by the Caco-2 cells were significantly higher in cereals fortified with FSH than with EI, obtaining intermediate values for the other two iron fortificants. MDFP induced higher expression of iron transporters Zip-14 and HEPH than other iron sources. FSH promoted the highest iron storage protein ferritin, followed by FF and MDFP, while EI presented the lowest in vitro bioavailability due to its low solubility. This work demonstrated that iron absorption, storage, and gene expression of transporters depend on the source of iron. These are important challenges to be taken into consideration when assessing the potential of iron fortificants.