Bioavailability of Elemental Iron Powders to Rats Is Less than Bakery-Grade Ferrous Sulfate and Predicted by Iron Solubility and Particle Surface Area

Abstract

Foods are fortified with elemental forms of iron to reduce iron deficiency. However, the nutritional efficacy of current, commercially produced elemental iron powders has not been verified. We determined the bioavailability of six commercial elemental iron powders and examined how physicochemistry influences bioavailability. Relative biological value (RBV) of the iron powders was determined using a hemoglobin repletion/slope ratio method, treating iron-deficient rats with repletion diets fortified with graded quantities of iron powders, bakery-grade ferrous sulfate or no added iron. Iron powders were assessed physicochemically by measuring iron solubility in hydrochloric acid at pH 1.0 and 1.7, surface area by nitrogen gas adsorption and surface microstructure by electron microscopy. Bioavailability from the iron powders, based on absolute iron intake, was significantly less than from FeSO4 (100%; P < 0.05) with the following rank order: Carbonyl (64%; Ferronyl, U.S.) > Electrolytic (54%; A-131, U.S.) > Electrolytic (46%; Electrolytic Iron, India) > H-Reduced (42%; AC-325, U.S.) > Reduced (24%; ATOMET 95SP, Canada) > CO-Reduced (21%; RSI-325, Sweden). Solubility testing of the iron powders resulted in different relative rankings and better RBV predictability with increasing time at pH 1.7 (R2 = 0.65 at 150 min). The prediction was improved with less time and lower pH (R2 = 0.82, pH 1.0 at 30 min). Surface area, ranging from 90 to 370 m2/kg, was also highly predictive of RBV (R2 = 0.80). Bioavailability of iron powders is less than bakery-grade ferrous sulfate and varies up to three times among different commercial forms. Solubility at pH 1.0 and surface area were predictive of iron bioavailability in rats.

Effect of dephytinization on bioavailability of iron, calcium and zinc from infant cereals assessed in the Caco-2 cell model

“…Since iron solubility, iron retention, transport efficiency, and uptake efficiency percentages can be used as bioavailability predictors [8,26,27] , our results showed that three of the four infant cereals analyzed after phytase treatment increased iron bioavailability. The source of iron used for the enrichment of infant cereals (elemental iron) plays an important role in iron solubility [28] ; in this regard, values found in our study were lower than those reported by other authors [29,30] for the same element, probably due to the phytate content or fiber components from cereals, the different pH conditions applied for the assays [29] , or the previously reported the inhibitory effect of calcium on iron availability [10] since infant cereals used in this study were calcium-enriched. Differences in iron bioavailability parameters between dephytinized infant cereals could indicate that other components of infant cereals can also decrease iron bioavailability; in this regard, it has been reported that some dietary fiber components can bind mineral ions decreasing their bioavailability [30,31] .…”

“…The source of iron used for the enrichment of infant cereals (elemental iron) plays an important role in iron solubility [28] ; in this regard, values found in our study were lower than those reported by other authors [29,30] for the same element, probably due to the phytate content or fiber components from cereals, the different pH conditions applied for the assays [29] , or the previously reported the inhibitory effect of calcium on iron availability [10] since infant cereals used in this study were calcium-enriched. Differences in iron bioavailability parameters between dephytinized infant cereals could indicate that other components of infant cereals can also decrease iron bioavailability; in this regard, it has been reported that some dietary fiber components can bind mineral ions decreasing their bioavailability [30,31] . Commercial infant cereal (Multicereals) showed the highest values of iron bioavailability parameter measures which can be justified because of its lower molar ratio of phytate to iron, compared to eight cereals-honey, rice cream and Glutenfree cereals.…”

Efficiency of Carbonyl Iron in Prevention of Anaemia in Piglets

“…it is less soluble at higher pH. It should be taken into account that the previously cited bioavailabilities of carbonyl iron (Devasthali et al 1991;Swain et al 2003) were obtained at gastric pH below 2. Because of relatively high pH of gastric content in suckling piglets, the negative effect of gastric pH on carbonyl iron utilization could be expected.…”

“…With carbonyl iron, however, only that fraction solubilized by gastric acid is available for absorption. According to Swain et al (2003) the bioavailability of carbonyl iron in rats is 64% of that of ferrous sulphate. Devasthali et al (1991) found in humans that the bioavailability of carbonyl iron was about 70% of that of ferrous sulphate.…”

“…This is also in agreement with our previous study where we have demonstrated the same efficiency of a double dose of 200 mg In addition, the rate of solubilization is restricted by the rate of gastric acid production (Huebers et al 1986). Swain et al (2003) showed that solubility of carbonyl iron depends on gastric pH, i.e. it is less soluble at higher pH.…”