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Purpose An iron-enriched yeast able to lyse at body temperature was developed for iron fortification of chilled dairy products. The aim was to evaluate iron (Fe) absorption from iron-enriched yeast or ferrous sulfate added to fresh cheese. Methods Two stable isotope studies with a crossover design were conducted in 32 young women. Fe absorption from fresh cheese fortified with iron-enriched yeast (2.5 mg 58 Fe) was compared to that from ferrous sulfate (2.5 mg 57 Fe) when ingested with fresh cheese alone or with fresh cheese consumed with bread and butter. Iron absorption was determined based on erythrocyte incorporation of isotopic labels 14 days after consumption of the last test meal. Results Geometric mean fractional iron absorption from fresh cheese fortified with iron-enriched yeast consumed alone was significantly lower than from the cheese fortified with FeSO 4 (20.5 vs. 28.7 %; p  = 0.0007). When the fresh cheese was consumed with bread and butter, iron absorption from both fortificants decreased to 6.9 % from the iron-enriched yeast compared to 8.4 % from ferrous sulfate. The relative bioavailability of the iron-enriched yeast compared to ferrous sulfate was 0.72 for the cheese consumed alone and 0.82 for cheese consumed with bread and butter ( p  = 0.157). Conclusions Iron from iron-enriched yeast was 72–82 % as well absorbed as ferrous sulfate indicating that the yeast lysed during digestion and released its iron.

Fossil-fuel emissions may impact phytoplankton primary productivity and carbon cycling by supplying bioavailable Fe to remote areas of the ocean via atmospheric aerosols. However, this path-way has not been confirmed by field observations of anthropogenic Fe in seawater. Here we present high-resolution trace-metal concentrations across the North Pacific Ocean (158°W from 25°to 42°N). A dissolved Fe maximum was observed around 35°N, coincident with high dissolved Pb and Pb isotope ratios matching Asian industrial sources and confirming recent aerosol deposition. Ironstable isotopes reveal in situ evidence of anthropogenic Fe in seawater, with low δ56Fe (−0.23‰ > δ56Fe > −0.65‰) observed in the region that is most influenced by aerosol deposition. An isotope mass balance suggests that anthropogenic Fe contributes 21–59% of dissolved Fe measured between 35° and 40°N. Thus, anthropogenic aerosol Fe is likely to be an important Fe source to the North Pacific Ocean.

Background and aims Paddy management results in frequent redox cycles of the soil and thus changes in the terrestrial iron (Fe) cycle. We intended to test that the increasing duration of paddy management and the increasing frequency of soil redox cycles leave their fingerprint on Fe isotope composition of paddy systems, which could subsequently be used to deduce the origin of rice plants as related to the extent of past soil paddy management. Methods We sampled soil and rice plants of a paddy chronosequence in China with rice cultivation history up to 2000 years and determined the changes of soil Fe pools and Fe isotope composition of the soil and rice plants. Results Prolonged paddy management reduced Fe concentrations in submerged topsoil leading to an enrichment of heavy Fe isotopes, with the δ 56 Fe values 0.12‰ heavier than the parent material after 2000 years. Particularly, Fe oxides were lost quickly, while exchangeable and organic-associated Fe continuously accumulated during paddy management and played an increasing role in the plant-available Fe pool in the topsoil. The Fe content in rice also increased with paddy age, while its Fe isotope composition did not reflect that of paddy soil but resembled that of the Fe plaques on the roots. Conclusion Prolonged rice cropping altered the biological contribution in the terrestrial Fe cycle. However, while soil Fe pools that are closely linked with biological activities were affected rather quickly, the changes in the whole soil Fe system were detectable only after a millennium of paddy management.

Purpose A technological gap exists for the iron (Fe) fortification of difficult-to-fortify products, such as wet and acid food products containing polyphenols, with stable and bioavailable Fe. Fe picolinate, a novel food ingredient, was found to be stable over time in this type of matrix. The objective of this study was to measure the Fe bioavailability of Fe picolinate in a complementary fruit yogurt. Methods The bioavailability of Fe picolinate was determined using stable iron isotopes in a double blind, randomized cross-over design in non-anemic Swiss women ( n  = 19; 25.1 ± 4.6 years). Fractional Fe absorption was measured from Fe picolinate (2.5 mg 57 Fe per serving in two servings given morning and afternoon) and from Fe sulfate (2.5 mg 54 Fe per serving in two servings given morning and afternoon) in a fortified dairy complementary food (i.e. yogurt containing fruits). Fe absorption was determined based on erythrocyte incorporation of isotopic labels 14 days after consumption of the last test meal. Results Geometric mean (95% CI) fractional iron absorption from Fe picolinate and Fe sulfate were not significantly different: 5.2% (3.8–7.2%) and 5.3% (3.8–7.3%) (N.S.), respectively. Relative bioavailability of Fe picolinate versus Fe sulfate was 0.99 (0.85–1.15). Conclusion Therefore, Fe picolinate is a promising compound for the fortification of difficult-to-fortify foods, to help meet Fe requirements of infants, young children and women of childbearing age.

This paper introduces an enhanced technique for analyzing iron isotopes in complex marine and biological samples. A dedicated iron purification method for biological marine matrices, utilizing three ion exchange columns, is validated. The MC-ICPMS in pseudo-high-resolution mode determines precise iron isotopic ratios, with sensitivity improved through the DSN-100 desolvating nebulizer system and Apex-IR. Only 2 µg of iron on DSN versus 1 µg on Apex is needed for six replicates (30–60 times improvement) while 10 to 20 µg is required for a single measurement on a wet system considering the resolution power (Rp) is maintained at 11,000–13,000. The Ni-doping method with a Fe/Ni ratio of 1 yields more accurate isotopic ratios than standard-sample bracketing alone. Measurement reproducibility of triplicate samples from marine biological experiments on MC-ICPMS is ± 0.03‰ (2SD) for δ56Fe and ± 0.07‰ for δ57Fe (2SD). This study introduces a novel iron purification process specifically designed for marine and biological samples, enhancing sensitivity and enabling more reliable measurements with smaller sample sizes and reduced uncertainties. It proposes iron isotopic compositions for biological reference materials, offering a valuable reference dataset in diverse scientific disciplines.

— The GEOCHEQ_Isotope software package, previously developed to calculate chemical and isotopic equilibria of carbon and oxygen in hydrothermal and hydrogeochemical systems by minimizing Gibbs energy, was extended to the simultaneous calculation of isotopic effects of carbon, oxygen, and iron (the main objective of the study). As for carbon and oxygen, the β-factor formalism was used to develop algorithms and a database for the calculation of iron isotopic effects. According to the developed algorithm, the Gibbs energy G *( P , T ) of formation of a rare isotopologue was calculated through the Gibbs energy of formation of the main isotopologue taking into account the value of the 56 Fe/ 54 Fe β-factor of this substance and the mass ratio of 54 Fe and 56 Fe isotopes. The approximation of ideal isotope mixture was used. The temperature dependence of the β-factor is unified in the form of a third-order polynomial by inverse even degrees of absolute temperature. Based on a critical analysis of currently available data on equilibrium isotopic factors obtained by different methods (elastic and inelastic γ-resonance scattering, isotope exchange experiments, and ab-initio calculations), the main result was obtained: for the first time, internally consistent database on iron β-factors of minerals and water complexes was developed. To develop the database, minerals and aqueous complexes for which the estimates of the equilibrium fractionation factors of iron isotopes obtained by different methods exist and consistent within the error of the methods have been identified: metallic iron (α-Fe), hematite, magnetite, siderite, pyrite, and the aqueous complexes and . The values of the iron β-factors for these minerals and aqueous complexes, accepted as reference ones, formed the “mainstay” of the developed database. Considering that the equilibrium isotopic shifts of iron between minerals and water complexes are estimated much more accurately within the framework of one method rather than the corresponding β-factors, the database was made consistent by linking the ln β values for minerals and water complexes to the reference ln β values. The application of the GEOCHEQ_Isotope software package to the closed carbonaceous hydrothermal system H 2 O–CO 2 –Fe 2 O 3 –FeO–CaO ( T = 200°C, P = 16–50 bar) has shown the possibility of its use for the calculation of changes in mineral composition and isotopic effects on oxygen, carbon, and iron.

We measured non-haem Fe absorption with and without added Ca in a short-term feeding study, in thirteen women with marginal Fe status, by the use of a double stable isotope technique. Supplementing 500 mg Ca as calcium carbonate significantly (P = 0·0009) reduced Fe absorption from a single meal from 10·2 % (range 2·2–40·6) to 4·8 % (range 0·7–18·9). A significant inverse correlation in the absence ( − 0·67, P = 0·010) and presence ( − 0·58, P = 0·037) of Ca, respectively, was found between Fe absorption and Fe stores measured by serum ferritin (SF). Wide variation in Fe absorption was observed between individuals in the absence and in the presence of Ca, despite pre-selection of participants within a relatively narrow range of iron stores (SF concentrations). Correction of Fe absorption data based on group mean SF was not found to be useful in reducing the inter-individual variability in iron absorption. It appears that selecting a study group with a narrow initial range of Fe stores does not necessarily reduce the inter-individual variability in Fe bioavailability measurements. These results support the hypothesis that body Fe stores, although an important determinant of dietary Fe absorption, are not the main factor that determines Fe absorption under conditions of identical dietary intake in subjects with low Fe stores.

Background: Iron is an essential element for critical biological functions, with iron deficiency negatively affecting growth and brain development and iron excess associated with adverse effects. The goal of this review is to provide a comprehensive assessment of up-to-date evidence on iron absorption measured isotopically in children, preterm infants, and full-term infants, up to 24 months of age. Methods: Search databases included Pubmed, Cochrane, Web of Science, and Scopus from a date range of 1 January 1953 to 22 July 2024. The included articles were experimental studies with iron absorption outcomes measured by isotopic techniques. The risk of bias was assessed using the Cochrane Risk of Bias Tool. Results: A total of 1594 records were identified from databases, and 37 studies were included in the quality review with a total of 1531 participants. Article results were grouped by study commonality: absorption and red blood cell incorporation, type of milk feedings, additives to improve absorption, how and when to supplement with iron, and iron forms and complimentary foods. Conclusions: The results from this review support the current recommendations of oral iron supplementation. Iron from breast milk has high bioavailability, and unmodified cow’s milk reduces iron absorption. Supplemental iron is required at 4–6 months for healthy, full-term infants and sooner for preterm infants. Ascorbic acid increases iron absorption in full-term infants and children. Lactoferrin and prebiotics are promising candidates for enhancing iron absorption, but they require further investigation. Research evidence of iron absorption mechanisms and modulating factors in preterm infants is limited and should be a research priority.

Many studies have shown that the average iron (Fe) isotope compositions of mantle-derived rocks, mantle peridotite and model mantle are close to those of chondrites. Therefore, it is considered that chondrite values represent the bulk Earth Fe isotope composition. However, this is a brave assumption because nearly 90% of Fe of the Earth is in the core, where its Fe isotope composition is unknown, but it is required to construct bulk Earth Fe isotope composition. We approach the problem by assuming that the Earth’s core separation can be approximated in terms of the Sudbury-type Ni-Cu sulfide mineralization, where sulfide-saturated mafic magmas segregate into immiscible sulfide liquid and silicate liquid. Their density/buoyancy controlled stratification and solidification produced net-textured ores above massive ores and below disseminated ores. The coexisting sulfide minerals (pyrrhotite (Po) > pentlandite (Pn) > chalcopyrite (Cp)) and silicate minerals (olivine (Ol) > orthopyroxene (Opx) > clinopyroxene (Cpx)) are expected to hold messages on Fe isotope fractionation between the two liquids before their solidification. We studied the net-textured ores of the Sudbury-type Jinchuan Ni-Cu sulfide deposit. The sulfide minerals show varying δ56Fe values (−1.37–−0.74‰ (Po) < 0.09–0.56‰ (Cp) < 0.53–1.05‰ (Pn)), but silicate minerals (Ol, Opx, and Cpx) have δ56Fe values close to chondrites (δ56Fe = −0.01 ± 0.01‰). The heavy δ56Fe value (0.52–0.60‰) of serpentines may reflect Fe isotopes exchange with the coexisting pyrrhotite with light δ56Fe. We obtained an equilibrium fractionation factor of Δ56Fesilicate-sulfide ≈ 0.51‰ between reconstructed silicate liquid (δ56Fe ≈ 0.21‰) and sulfide liquid (δ56Fe ≈ −0.30‰), or Δ56Fesilicate-sulfide ≈ 0.36‰ between the weighted mean bulk-silicate minerals (δ56Fe[0.70ol,0.25opx,0.05cpx] = 0.06‰) with weighted mean bulk-sulfide minerals (δ56Fe ≈ −0.30‰). Our study indicates that significant Fe isotope fractionation does take place between silicate and sulfide liquids during the Sudbury-type sulfide mineralization. We hypothesize that significant iron isotope fractionation must have taken place during core–mantle segregation, and the bulk Earth may have lighter Fe isotope composition than chondrites although Fe isotope analysis on experimental sulfide-silicate liquids produced under the varying mantle depth conditions is needed to test our results. We advocate the importance of further research on the subject. Given the close Fe-Ni association in the magmatic mineralization and the majority of the Earth’s Ni is also in the core, we infer that Ni isotope fractionation must also have taken place during the core separation that needs attention.

Isotopic analysis of human blood and liver and muscle tissue indicates that each individual bears a long-term iron (Fe) isotope signature in the blood. Blood and tissue differ slightly in isotopic composition and are depleted by up to 2.6 per mil in56Fe relative to54Fe when compared to dietary Fe. The56Fe/54Fe isotope ratio in the blood of males is, on average, lower by 0.3 per mil than that of females. These results suggest that Fe isotope effects in the blood reflect differences in intestinal Fe absorption between individuals and genotypes.