Food iron absorption measured by an extrinsic tag

Bioavailability of Australian pre-schooler iron intakes at specific eating occasions is low

PURPOSE

Poor bioavailability may contribute to iron deficiency among children in high-resource countries, but iron bioavailability of Australian pre-schooler diets is unknown. This study aimed to estimate the bioavailability of Australian pre-schooler iron intakes across the day and by eating occasions to identify optimal timing for intervention, by using five previously developed algorithms, and to estimate the proportion of children with intakes of absorbable iron below the requirements.

METHODS

Dietary data of children aged 2 to < 6 y (n = 812) from the 2011-12 National Nutrition and Physical Activity Survey were collected via two 24-h recalls. Usual food and nutrient intakes were estimated via Multiple Source Method. Phytate, polyphenol, and heme iron values were sourced from international databases or the literature. Five previously published algorithms were applied to observed dietary data to estimate iron bioavailability and calculate the prevalence of children with intakes of absorbable iron below requirements.

RESULTS

Pre-schooler daily iron bioavailability was low (2.7-10.5%) and corresponded to intakes of 0.18-0.75 mg/d of absorbable iron. The proportion of children with inadequate intakes of absorbable iron ranged between 32 and 98%. For all eating occasions, dinner offered iron of the greatest bioavailability (4.2-16.4%), while iron consumed at breakfast was of the lowest bioavailability (1.2-5.6%).

CONCLUSION

Future strategies are required to improve intakes of bioavailable iron for pre-schoolers to prevent the risk of deficiency. These strategies could include the encouragement of concomitant consumption of enhancers of iron absorption with iron-rich sources, particularly at breakfast.

Iron Nutrition of Pre-Schoolers in High-Income Countries: A Review

Pre-schoolers are vulnerable to iron deficiency, which, in high-resource countries, is mainly caused by suboptimal or poorly absorbable iron intakes. This review examines the prevalence of inadequate iron intakes and status, and the non-dietary factors associated with these, among children aged between 2 and 5 years within high-income countries. It then considers the quality of the pre-schooler diet in terms of dietary factors, dietary patterns, and iron intakes. Additionally, it discusses the assessment of iron bioavailability and examines the various methods used to estimate the amount of absorbable iron in pre-schooler diets. Knowledge of the adequacy of iron intakes and bioavailability of iron intakes, and dietary patterns associated with iron intakes can facilitate the design and implementation of effectively targeted community-based intervention studies to improve iron intakes and iron bioavailability to minimise the risk of iron deficiency.

Lower Non-Heme Iron Absorption in Healthy Females from Single Meals with Texturized Fava Bean Protein Compared to Beef and Cod Protein Meals: Two Single-Blinded Randomized Trials

Meat analogs based on plant protein extracts are rising in popularity as meat consumption declines. A dietary shift away from meat, which has a high iron bioavailability, may have a negative effect on the amount of iron absorbed from the diet. Iron absorption from legumes cultivated in regions not suitable for soy production, such as fava bean, has not yet been explored. The aim of this study was to evaluate non-heme iron absorption from a meal with texturized fava bean protein compared to beef and cod protein meals. The study included two single-blinded iron isotope trials in healthy Swedish women of the ages 18–45 years, each of whom served as their own control. The participants were served matched test meals containing beef and fava bean protein (Study 1) or cod and fava bean protein (Study 2) with radiolabeled non-heme iron 55Fe and 59Fe. The absorption of non-heme iron from test meals was measured by whole-body counting and erythrocyte incorporation. The absorption of non-heme iron, measured as erythrocyte incorporation ratio, from beef protein meal was 4.2 times higher compared to texturized fava bean meal, and absorption from cod protein meal was 2.7 times higher compared to the fava bean meal. The adjusted non-heme iron absorption, normalized to a 40% reference dose uptake, was 9.2% for cod protein meal, 21.7% for beef protein meal, and 4.2% for texturized fava bean meal. A fava bean protein meal has markedly lower iron bioavailability in healthy females compared with a meal of beef or cod protein. Therefore, a dietary shift from meat and fish protein to fava bean protein may increase the risk of iron deficiency.

Dietary patterns of Australian pre-schoolers and associations with haem and non-haem iron intakes

PURPOSE

To describe Australian pre-schooler dietary patterns and examine their associations with dietary iron intakes.

METHODS

Dietary data of children (n = 812, 2 to < 6 years old) from the 2011-12 National Nutrition and Physical Activity Survey were collected via two non-consecutive 24-h recalls and analysed using AUSNUT 2011-13. Usual food and nutrient intakes were estimated via Multiple Source Method. Principal component analysis was used to extract dietary patterns from 32 food groups. Associations between dietary patterns and energy-adjusted iron intakes were assessed using linear regression, accounting for the complex survey design.

RESULTS

Mean (SD) usual total dietary and haem iron intakes were 6.3 (1.9) and 0.5 (0.3) mg/day, respectively. Three dietary patterns were identified, explaining 14% of the variance. Pattern 1 (positive loadings for cheese, breads, fats and oils, and water) was positively associated with total dietary iron intakes (β = 0.08, 95% CI 0.01, 0.15). Pattern 3 (positive loadings for red meat, fortified fruit and vegetable products, and sauces and spreads) was negatively associated with total dietary iron (β = - 0.08, 95% CI - 0.14, - 0.01) and non-haem iron (β = - 0.09, 95% CI - 0.15, - 0.02) intakes. No dietary patterns were associated with haem iron intakes.

CONCLUSIONS

Three main patterns characterise Australian pre-schooler diets. The pattern with which dietary iron is positively associated is predominately characterised by non-haem iron sources and non-iron-fortified foods. Future research is required to estimate the iron bioavailability of Australian pre-schooler diets.

Mapping the Inorganic and Proteomic Differences among Different Types of Human Teeth: A Preliminary Compositional Insight

In recent years, studies on mineralized tissues are becoming increasingly popular not only due to the diverse mechanophysical properties of such materials but also because of the growing need to understand the intricate mechanism involved in their assembly and formation. The biochemical mechanism that results in the formation of such hierarchical structures through a well-coordinated accumulation of inorganic and organic components is termed biomineralization. Some prime examples of such tissues in the human body are teeth and bones. Our current study is an attempt to dissect the compositional details of the inorganic and organic components in four major types of human teeth using mass spectrometry-based approaches. We quantified inorganic materials using inductively coupled plasma resonance mass spectrometry (ICP-MS). Differential level of ten different elements, Iron (Fe), Cadmium (Cd), Potassium (K), Sulphur (S), Cobalt (Co), Magnesium (Mg), Manganese (Mn), Zinc (Zn), Aluminum (Al), and Copper (Cu) were quantified across different teeth types. The qualitative and quantitative details of their respective proteomic milieu revealed compositional differences. We found 152 proteins in total tooth protein extract. Differential abundance of proteins in different teeth types were also noted. Further, we were able to find out some significant protein-protein interaction (PPI) backbone through the STRING database. Since this is the first study analyzing the differential details of inorganic and organic counterparts within teeth, this report will pave new directions to the compositional understanding and development of novel in-vitro repair strategies for such biological materials.

Mass spectrometry-based analytical developments to link iron speciation to iron bioavailability in maize

A sequential fractionation procedure based on (i) water extraction, (ii) hexane extraction, (iii) saccharification, and (iv) proteolysis was developed to provide the first ever data on the molecular distribution of iron in maize. This was completed by the operational determination of the iron bioavailability using an in-vitro simulated model for gastro-intestinal digestion. The coupling of hydrophilic interaction chromatography (HILIC) and size exclusion chromatography (SEC) with the parallel detection by inductively coupled plasma mass spectrometry (ICP-MS) and high resolution electrospray mass spectrometry (HR-ESI-MS) allowed the identification of water-soluble Fe(III)-mugineate, Fe(III)-(citrate)₂, and Fe(III)₂-(phytate)₂. The procedures were applied to study some well characterized maize varieties having shown previously differences in iron bioavailability during cell culture and animal model feeding studies. The combined analytical methods developed in this work could unambiguously discriminate low from high Fe bioavailable seeds in these closely related maize varieties.

Physiological requirements for iron in women of reproductive age assessed by the stable isotope tracer technique

BACKGROUND

Iron nutrition is important for the health of women of reproductive age, and defining the physiologic requirement for iron can help them accurately plan the iron intake. However, research on the physiologic requirement for iron in women is insufficient worldwide. This study aimed to further improve the methodology and get more precise data for the physiological requirements for iron in women of reproductive age on the basis of our previous study.

METHOD

Sixty-one women of reproductive age who had not been pregnant before and during the whole study were included from Hebei province, China in 2015. Each subject participated in a 2-week metabolic trial with consuming 50 mg of the stable isotope 58Fe, and were then followed for ~ 800 days. The abundance of 58Fe and the total iron concentration in the circulation were measured using multi-collector inductively-coupled plasma mass spectrometry and atomic absorption spectroscopy. The physiologic requirement for iron in women of reproductive age was then calculated.

RESULTS

The average iron circulation rate was 80.4%, and the steady period started from about 1 year. The average physiological requirement for iron of 21 subjects obtained by formula calculation was 1.55 mg/d and 23.63 μg.kg- 1.d- 1 after adjustment for body mass, and that of 33 subjects obtained by linear regression was 1.29 mg/d, 20.98 μg.kg- 1.d- 1 after adjustment for body mass. The results by two methods showed no significant difference. The EAR and RNI calculated from this results was 11-13 mg/d and 15-18 mg/d, respectively, both of which were slightly lower than the recommended value in Chinese Dietary Reference Intake (2013).

CONCLUSION

The physiological requirements for iron in women of reproductive age were in accordance with other studies, while the EAR and RNI calculated from which were slightly lower than Chinese present recommended value.

TRIAL REGISTRATION

ChiCTR, ChiCTR-OCH-14004302. Registered 14 February 2014, http://www.chictr.org.cn/enindex.aspx.

Organic iron absorption by in situ ligated jejunal and ileal loops of broilers

The objective of this study was to determine the effect of organic and inorganic Fe sources on the Fe absorption and gene expression of Fe and amino acid transporters in the ligated jejunal and ileal segments of broilers. The in situ ligated jejunal and ileal loops from Fe-deficient broiler chicks (28-d-old) were perfused with Fe solutions containing 0, 3.58, or 7.16 mM Fe from one of the following Fe sources: Fe sulfate (FeSO4∙7H2O), the mixtures of FeSO4∙7H2O with either Met or Gly, Fe-Gly chelate, or three Fe-amino acid or protein chelates with weak, moderate or extremely strong chelation strengths (Fe-Met W, Fe-Pro M, or Fe-Pro ES), respectively, for up to 30 min. Iron absorption was increased (P < 0.0001) as the perfused Fe concentrations increased, and no differences (P > 0.07) were detected in the Fe absorption between the jejunum and ileum. Regardless of intestinal segments, Fe absorption was higher (P < 0.006) for Fe-Pro ES and Fe-Pro M than for FeSO4·7H2O, and for Fe-Pro ES than for Fe-Met W. Glycine but not Met supplementation increased (P < 0.03) the absorption of Fe as FeSO4. Regardless of Fe source, Fe addition inhibited (P < 0.05) the mRNA expressions of divalent metal transporter 1 (DMT1) in the jejunum and ileum, but enhanced (P < 0.05) the mRNA expressions of l-type amino transporter 1 (LAT1) and B0-type amino acid transporter 1 (B0AT1) in the jejunum and ileum. No differences (P > 0.05) among different Fe sources were observed in the mRNA expression levels of Fe and amino acid transporters in both the jejunum and the ileum. The mRNA expression levels of DMT1, ferroportin 1, B0AT1, or y+LAT1 were higher (P < 0.0001), but those of excitatory amino acid transporter 3, LAT1, or y+l-type amino transporter 2 were lower (P < 0.04) in the jejunum than in the ileum. The supplementation of inorganic or organic Fe had no effect (P > 0.14) on the protein expression levels of DMT1 and FPN1 in the jejunum and ileum. The above results indicate that organic Fe sources with stronger chelation strengths showed higher Fe absorption in the jejunum and ileum of broiler chicks. Glycine was more effective in facilitating Fe absorption than Met as a ligand. The mRNA expressions of Fe and amino acid transporters in the jejunum were different from those in the ileum. The DMT1, LAT1, and B0AT1 might be involved in the Fe absorption in the jejunum or ileum of broilers.

Biomarkers of Nutrition for Development (BOND)-Iron Review

This is the fifth in the series of reviews developed as part of the Biomarkers of Nutrition for Development (BOND) program. The BOND Iron Expert Panel (I-EP) reviewed the extant knowledge regarding iron biology, public health implications, and the relative usefulness of currently available biomarkers of iron status from deficiency to overload. Approaches to assessing intake, including bioavailability, are also covered. The report also covers technical and laboratory considerations for the use of available biomarkers of iron status, and concludes with a description of research priorities along with a brief discussion of new biomarkers with potential for use across the spectrum of activities related to the study of iron in human health.The I-EP concluded that current iron biomarkers are reliable for accurately assessing many aspects of iron nutrition. However, a clear distinction is made between the relative strengths of biomarkers to assess hematological consequences of iron deficiency versus other putative functional outcomes, particularly the relationship between maternal and fetal iron status during pregnancy, birth outcomes, and infant cognitive, motor and emotional development. The I-EP also highlighted the importance of considering the confounding effects of inflammation and infection on the interpretation of iron biomarker results, as well as the impact of life stage. Finally, alternative approaches to the evaluation of the risk for nutritional iron overload at the population level are presented, because the currently designated upper limits for the biomarker generally employed (serum ferritin) may not differentiate between true iron overload and the effects of subclinical inflammation.

Iron physiological requirements in Chinese adults assessed by the stable isotope labeling technique

Background

Iron is a kind of essential trace mineral in the human body, while the studies on its physiological requirement are very limited recently, especially in China. And most studies were performed with the radioisotope tracer technique, which was harmful to health. This study aimed to first get the value of iron physiological requirements in Chinese adults assessed by the stable isotope labeling technique.

Methods

Forty-four eligible young Chinese healthy adults were randomly recruited from the Bethune Military Medical College (Shijiazhuang, Hebei, China) between January 2010 and March 2011, and 19 subjects were included in the final data analysis. After adaptive diets and observation, subjects received ⁵⁸Fe intravenously. The baseline venous blood sample and general information were collected on day 0. Venous blood samples were also collected on day 14, 30, 60, 100, 120, 150, 240, 330, 425, 515, 605, 767, 1155, respectively. The blood samples were acid digested by a Microwave Digestion System and then analyzed by the MC-ICP-MS and Atomic Absorption Spectroscopy to get the abundance of Fe isotopes and the total iron concentration respectively. The circulation rate (the proportion of blood iron to whole body iron) could be calculated by the intake amount, background content and the peak isotope content. When the abundance changed stably, the iron physiological requirement could be calculated by the iron loss in a period of time.

Results

The abundance of ⁵⁸Fe reached its peak on day 14, and changed stably from day 425. The average circulation rate was 84%, with no significance difference between the 2 genders. The mean iron requirement in females was 1101.68 μg/d, and the mean requirement adjusted by body weight was 20.69 μg/kg.d. For males, the mean iron requirement was 959.9 μg/d, and the requirement adjusted by body weight was 14.04 μg/kg.d.

Conclusion

Our study has obtained the data about the iron physiological requirements of Chinese adults using stable isotope labeling technique, which could provide the basis for adjusting iron DRIs of Chinese people in the future.

Trial registration

The trial was registered at the Chinese Clinical Trial Registry (No: ChiCTR-TRC-09000581).

Effect of iron source on iron absorption and gene expression of iron transporters in the ligated duodenal loops of broilers

This experiment was conducted to investigate the effect of iron source on Fe absorption and the gene expression of divalent metal transporter 1 (DMT1) and ferroportin 1 (FPN1) in the ligated duodenal loops of broilers. The in situ ligated duodenal loops from Fe-deficient broiler chicks (28-d-old) were perfused with Fe solutions containing 0 to 14.33 mmol Fe/L from 1 of the following: Fe sulfate (FeSO∙7HO), Fe methionine with weak chelation strength (Fe-Met W; chelation strength is expressed as quotient of formation [Q] value, Q = 1.37), Fe proteinate with moderate chelation strength (Fe-Prot M; Q = 43.6), and Fe proteinate with extremely strong chelation strength (Fe-Prot ES; Q = 8,590) for up to 30 min. The gene expression of DMT1 and FPN1 in the duodenal loops from the control group and the groups treated with 3.58 mmol Fe/L from 1 of 4 Fe sources was analyzed. The absorption kinetics of Fe from different Fe sources in the duodenum followed a saturated carrier-dependent transport process. The maximum transport rate (J) values in the duodenum were greater ( < 0.03) for Fe-Prot ES and Fe-Prot M than for Fe-Met W and FeSO∙7HO. The Fe perfusion inhibited ( < 0.05) the mRNA expression of but enhanced ( < 0.0008) the mRNA expression of in the duodenum and had no effect ( > 0.14) on the protein expression levels of the 2 transporters. These results indicated that organic Fe sources with greater Q values showed higher Fe absorption; however, all Fe sources followed the same saturated carrier-dependent transport process in the duodenum, and DMT1 and FPN1 might participate in Fe absorption in the duodenum of broilers regardless of Fe source.

Effect of Mentha piperita (Labiatae) and Mentha spicata (Labiatae) on iron absorption in rats

Aim: The effect of Mentha piperita (Labiatae) and Mentha spicata (Labiatae) teas, which contain different phenol compounds, on iron metabolism was studied. These teas grow in different areas of the city of Isparta, Turkey. These herbals were given to the rats in tea. Methods: Forty-eight male Wistar albino rats weighing 200-250 g were used for this study. The rats were divided into four groups of 12 animals: Group I received no herbal tea (control group); Group II received 20 g/L M. piperita tea; Group III received 20 g/L M. spicata tea; Group IV received 40 g/L M. spicata tea. Herbal teas were prepared daily and provided at all times to the rats over 30 days as drinking water. Results: M. piperita tea caused a decrease in serum iron and ferritin levels P <0.05), and caused an increase in unsaturated iron-binding capacity (UIBC) P <0.01). M. spicata tea caused no significant change in serum iron, ferritin levels and UIBC P <0.05). Conclusion: Both herbal teas inhibited Fe absorption. Inhibition caused by M. spicata tea was dose dependent. Therefore, when drinking these teas, their effect should be considered, especially for children and anemic patients.

In Rwandese Women with Low Iron Status, Iron Absorption from Low-Phytic Acid Beans and Biofortified Beans Is Comparable, but Low-Phytic Acid Beans Cause Adverse Gastrointestinal Symptoms

BACKGROUND

Phytic acid (PA) is a major inhibitor of iron bioavailability from beans, and high PA concentrations might limit the positive effect of biofortified beans (BBs) on iron status. Low-phytic acid (lpa) bean varieties could increase iron bioavailability.

OBJECTIVE

We set out to test whether lpa beans provide more bioavailable iron than a BB variety when served as part of a composite meal in a bean-consuming population with low iron status.

METHODS

Dietary iron absorption from lpa, iron-biofortified, and control beans (CBs) (regular iron and PA concentrations) was compared in 25 nonpregnant young women with low iron status with the use of a multiple-meal crossover design. Iron absorption was measured with stable iron isotopes.

RESULTS

PA concentration in lpa beans was ∼10% of BBs and CBs, and iron concentration in BBs was ∼2- and 1.5-fold compared with CBs and lpa beans, respectively. Fractional iron absorption from lpa beans [8.6% (95% CI: 4.8%, 15.5%)], BBs [7.3% (95% CI: 4.0%, 13.4%)], and CBs [8.0% (95% CI: 4.4%, 14.6%)] did not significantly differ. The total amount of iron absorbed from lpa beans and BBs was 421 μg (95% CI: 234, 756 μg) and 431 μg (95% CI: 237, 786 μg), respectively, and did not significantly differ, but was >50% higher (P < 0.005) than from CBs (278 μg; 95% CI: 150, 499 μg). In our trial, the lpa beans were hard to cook, and their consumption caused transient adverse digestive side effects in ∼95% of participants. Gel electrophoresis analysis showed phytohemagglutinin L (PHA-L) residues in cooked lpa beans.

CONCLUSION

BBs and lpa beans provided more bioavailable iron than control beans and could reduce dietary iron deficiency. Digestive side effects of lpa beans were likely caused by PHA-L, but it is unclear to what extent the associated digestive problems reduced iron bioavailability. This trial was registered at clinicaltrials.gov as NCT02215278.

Probiotic strain Lactobacillus plantarum 299v increases iron absorption from an iron-supplemented fruit drink: a double-isotope cross-over single-blind study in women of reproductive age

Iron deficiency is common, especially among young women. Adding probiotics to foods could be one way to increase iron absorption. The aim of this study was to test the hypothesis that non-haem iron absorption from a fruit drink is improved by adding Lactobacillus plantarum 299v (Lp299v). Iron absorption was studied in healthy women of reproductive age using a single-blind cross-over design in two trials applying the double-isotope (⁵⁵Fe and ⁵⁹Fe) technique. In Trial 1, iron absorption from a fruit drink containing 10⁹ colony-forming units (CFU) Lp299v was compared with that from a control drink without Lp299v. Trial 2 had the same design but 10¹⁰ CFU were used. The test and control drinks contained approximately 5 mg of iron as ferrous lactate and were labelled with ⁵⁹Fe (B) and ⁵⁵Fe (A), respectively, and consumed on 4 consecutive days in the order AABB. Retention of the isotopes was measured with whole-body counting and in blood. Mean iron absorption from the drink containing 10⁹ CFU Lp299v (28·6(sd 12·5) %) was significantly higher than from the control drink (18·5(sd 5·8) %), n 10, P<0·028). The fruit drink with 10¹⁰ CFU Lp299v gave a mean iron absorption of 29·1(sd 17·0) %, whereas the control drink gave an absorption of (20·1(sd 6·4) %) (n 11, P<0·080). The difference in iron absorption between the 10⁹ CFU Lp299v and the 10¹⁰ CFU Lp299v drinks was not significant (P=0·941). In conclusion, intake of probiotics can increase iron absorption by approximately 50 % from a fruit drink having an already relatively high iron bioavailability.

Extrinsic Labeling of Staple Food Crops with Isotopic Iron Does Not Consistently Result in Full Equilibration: Revisiting the Methodology

Extrinsic isotopic labeling of food Fe has been used for over 50 years to measure Fe absorption. This method assumes that complete equilibration occurs between the extrinsic and the intrinsic Fe prior to intestinal absorption. The present study tested this assumption via in vitro digestion of varieties of maize, white beans, black beans, red beans, and lentils. Prior to digestion, foods were extrinsically labeled with (58)Fe at concentrations of 1, 10, 50, and 100% of the intrinsic (56)Fe. Following an established in vitro digestion protocol, the digest was centrifuged and the Fe solubilities of the extrinsic (58)Fe and the intrinsic (56)Fe were compared as a measure of extrinsic/intrinsic equilibration. In the beans, significantly more of the extrinsic Fe (up to 2-3 times, p < 0.001) partitioned into the supernatant. The effect varied depending upon the seed coat color, the harvest, and the concentration of the extrinsic Fe. For lentils and maize the extrinsic Fe tended to partition into the insoluble fraction and also varied depending on variety and harvest. There was no crop that consistently demonstrated full equilibration of the extrinsic Fe with the intrinsic Fe. These observations challenge the accuracy of Fe absorption studies in which isotopic extrinsic Fe was used to evaluate Fe absorption and bioavailability.

Is achlorhydria a cause of iron deficiency anemia?

We re-evaluated the old hypothesis that gastritis-induced achlorhydria is a cause of iron deficiency anemia (IDA) in humans. First, we analyzed the currently available research on the association between achlorhydria and IDA. When gastric acid secretion was measured after maximal stimulation, the frequency of achlorhydria (or severe hypochlorhydria) was 44% in patients with idiopathic IDA and 1.8% in healthy controls. In some patients with pernicious anemia, presumed achlorhydria preceded the development of IDA in time. However, we found no credible evidence that IDA caused gastritis or that IDA preceded the development of achlorhydria. Thus, correlational results favor achlorhydria as the causal factor in the association between achlorhydria and IDA. Second, we sought to determine whether gastritis and achlorhydria cause negative iron balance. When biosynthetic methods were used to isotopically label iron in food, achlorhydric patients were found to have severe malabsorption of nonheme iron, which persisted after the development of IDA. In 1 study, achlorhydria reduced the normal increase in heme-iron absorption from hemoglobin in response to iron deficiency. After an injection of isotopic iron into normal men, the physiologic loss of iron from the body was found to be 1 mg/d. Patients with chronic gastritis had excess fecal loss of isotopically tagged plasma iron. Calculations based on these results indicate that the absorption of iron from a typical Western diet by achlorhydric patients would be less than physiologic iron losses, creating a negative iron balance that could not be overcome by the adaptive increase in duodenal iron absorptive capacity that occurs in response to iron deficiency. The combination of results from these correlational and pathophysiologic studies supports the hypothesis that gastritis-induced achlorhydria can be an independent cause of IDA.

Review: The potential of the common bean (Phaseolus vulgaris) as a vehicle for iron biofortification

Common beans are a staple food and the major source of iron for populations in Eastern Africa and Latin America. Bean iron concentration is high and can be further increased by biofortification. A major constraint to bean iron biofortification is low iron absorption, attributed to inhibitory compounds such as phytic acid (PA) and polyphenol(s) (PP). We have evaluated the usefulness of the common bean as a vehicle for iron biofortification. High iron concentrations and wide genetic variability have enabled plant breeders to develop high iron bean varieties (up to 10 mg/100 g). PA concentrations in beans are high and tend to increase with iron biofortification. Short-term human isotope studies indicate that iron absorption from beans is low, PA is the major inhibitor, and bean PP play a minor role. Multiple composite meal studies indicate that decreasing the PA level in the biofortified varieties substantially increases iron absorption. Fractional iron absorption from composite meals was 4%–7% in iron deficient women; thus the consumption of 100 g biofortified beans/day would provide about 30%–50% of their daily iron requirement. Beans are a good vehicle for iron biofortification, and regular high consumption would be expected to help combat iron deficiency (ID).

Phytic acid concentration influences iron bioavailability from biofortified beans in Rwandese women with low iron status

BACKGROUND

The common bean is a staple crop in many African and Latin American countries and is the focus of biofortification initiatives. Bean iron concentration has been doubled by selective plant breeding, but the additional iron is reported to be of low bioavailability, most likely due to high phytic acid (PA) concentrations.

OBJECTIVE

The present study evaluated the impact of PA on iron bioavailability from iron-biofortified beans.

METHODS

Iron absorption, based on erythrocyte incorporation of stable iron isotopes, was measured in 22 Rwandese women who consumed multiple, composite bean meals with potatoes or rice in a crossover design. Iron absorption from meals containing biofortified beans (8.8 mg Fe, 1320 mg PA/100 g) and control beans (5.4 mg Fe, 980 mg PA/100 g) was measured with beans containing either their native PA concentration or with beans that were ∼50% dephytinized or >95% dephytinized.

RESULTS

The iron concentration of the cooked composite meals with biofortified beans was 54% higher than in the same meals with control beans. With native PA concentrations, fractional iron absorption from the control bean meals was 9.2%, 30% higher than that from the biofortified bean meals (P < 0.001). The quantity of iron absorbed from the biofortified bean meals (406 μg) was 19% higher (P < 0.05) than that from the control bean meals. With ∼50% and >95% dephytinization, the quantity of iron absorbed from the biofortified bean meals increased to 599 and 746 μg, respectively, which was 37% (P < 0.005) and 51% (P < 0.0001) higher than from the control bean meals.

CONCLUSIONS

PA strongly decreases iron bioavailability from iron-biofortified beans, and a high PA concentration is an important impediment to the optimal effectiveness of bean iron biofortification. Plant breeders should focus on lowering the PA concentration of high-iron beans. This trial was registered at clinicaltrials.gov as NCT01521273.

Trace elements can influence the physical properties of tooth enamel

In previous studies, we showed that the size of apatite nanocrystals in tooth enamel can influence its physical properties. This important discovery raised a new question; which factors are regulating the size of these nanocrystals? Trace elements can affect crystallographic properties of synthetic apatite, therefore this study was designed to investigate how trace elements influence enamel's crystallographic properties and ultimately its physical properties. The concentration of trace elements in tooth enamel was determined for 38 extracted human teeth using inductively coupled plasma-optical emission spectroscopy (ICP-OES). The following trace elements were detected: Al, K, Mg, S, Na, Zn, Si, B, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Se and Ti. Simple and stepwise multiple regression was used to identify the correlations between trace elements concentration in enamel and its crystallographic structure, hardness, resistance to crack propagation, shade lightness and carbonate content. The presence of some trace elements in enamel was correlated with the size (Pb, Ti, Mn) and lattice parameters (Se, Cr, Ni) of apatite nanocrystals. Some trace elements such as Ti was significantly correlated with tooth crystallographic structure and consequently with hardness and shade lightness. We conclude that the presence of trace elements in enamel could influence its physical properties.

Iron and zinc nutrition in the economically-developed world: a review

This review compares iron and zinc food sources, dietary intakes, dietary recommendations, nutritional status, bioavailability and interactions, with a focus on adults in economically-developed countries. The main sources of iron and zinc are cereals and meat, with fortificant iron and zinc potentially making an important contribution. Current fortification practices are concerning as there is little regulation or monitoring of intakes. In the countries included in this review, the proportion of individuals with iron intakes below recommendations was similar to the proportion of individuals with suboptimal iron status. Due to a lack of population zinc status information, similar comparisons cannot be made for zinc intakes and status. Significant data indicate that inhibitors of iron absorption include phytate, polyphenols, soy protein and calcium, and enhancers include animal tissue and ascorbic acid. It appears that of these, only phytate and soy protein also inhibit zinc absorption. Most data are derived from single-meal studies, which tend to amplify impacts on iron absorption in contrast to studies that utilize a realistic food matrix. These interactions need to be substantiated by studies that account for whole diets, however in the interim, it may be prudent for those at risk of iron deficiency to maximize absorption by reducing consumption of inhibitors and including enhancers at mealtimes.

Phytic acid-to-iron molar ratio rather than polyphenol concentration determines iron bioavailability in whole-cowpea meal among young women

Limited data exist on iron absorption from NaFeEDTA and FeSO(4) in legume-based flours. The current study compared iron absorption from NaFeEDTA and FeSO(4) as fortificants within and between red and white varieties of cowpea with different concentrations of polyphenols (PP) but similar phytic acid (PA)-to-iron molar ratios. We performed a paired crossover study in young women (n = 16). Red-cowpea (high-PP) and white-cowpea (low-PP) test meals (Tubani) were each fortified with ((57)Fe)-labeled NaFeEDTA or ((58)Fe)-labeled FeSO(4) and were randomly administered. Iron absorption was measured as erythrocyte incorporation of stable iron isotopes. Per serving, the mean (±SD) PP concentrations of the white- and red-cowpea-based meals were 74 ± 3.6 and 158 ± 1.8 mg, respectively, and the molar ratio of PA to iron was 3.0 and 3.3. Iron bioavailabilities from red and white cowpeas were 1.4 and 1.7%, respectively, in NaFeEDTA-fortified meals and 0.89 and 1.2%, respectively, in FeSO(4)-fortified meals. Compared with FeSO(4), fortification with NaFeEDTA increased the amount of iron absorbed from either of the cowpea meals by 0.05 to 0.08 mg (P < 0.05). Irrespective of the fortificant used, there was no significant difference in the amount of iron absorbed from the 2 varieties of cowpea. The results suggest that NaFeEDTA is more bioavailable in legume-based flours compared with FeSO(4). In cowpea-based flours, the major determinant of low iron absorption may be the high molar ratio of PA to iron and not variations in PP concentration.

Manganese source affects manganese transport and gene expression of divalent metal transporter 1 in the small intestine of broilers

In the present study, two experiments were conducted to investigate the effect of Mn source on Mn transport and the expression of a Mn transporter, divalent metal transporter 1 (DMT1), in the small intestine of broilers. In Expt 1, in situ ligated duodenal loops from Mn-deficient chicks (29-d-old) were perfused with solutions containing 0-8.74 mmol Mn/l from either MnSO4, or one of two organic chelates of Mn and amino acids with moderate (OM) or strong (OS) chelation strength (Q(f)) up to 30 min. In Expt 2, Mn-deficient intact broilers (14-d-old) were fed a control diet (12.45 mg Mn/kg) or the control diet supplemented with 100 mg Mn/kg as one of all Mn sources for 14 d. The uptake kinetics of Mn from different Mn sources in the ligated duodenal loops followed a saturable process as determined by regression analysis of concentration-dependent uptake rates. The maximum transport rate (Jmax) and K(m) values, and DMT1 mRNA levels in the ligated duodenal loops were higher (P < 0.01) for OM and OS than for MnSO4. DMT1 mRNA levels were much higher (P < 0.01) in the duodenum than in the jejunum and ileum. Both DMT1 mRNA levels in the duodenum and plasma Mn contents from the hepatic portal vein of intact chicks on day 14 post-feeding increased (P < 0.05) in the following order: control < MnSO4 < OM < OS. These results indicated that organic Mn sources with stronger Q(f) showed higher Mn transport and absorption, and DMT1 might be involved in the regulation of organic Mn transport in the proximal small intestine of broilers.

A micronutrient powder with low doses of highly absorbable iron and zinc reduces iron and zinc deficiency and improves weight-for-age Z-scores in South African children

Micronutrient powders (MNP) are often added to complementary foods high in inhibitors of iron and zinc absorption. Most MNP therefore include high amounts of iron and zinc, but it is no longer recommended in malarial areas to use untargeted MNP that contain the Reference Nutrient Intake for iron in a single serving. The aim was to test the efficacy of a low-iron and -zinc (each 2.5 mg) MNP containing iron as NaFeEDTA, ascorbic acid (AA), and an exogenous phytase active at gut pH. In a double-blind controlled trial, South African school children with low iron status (n = 200) were randomized to receive either the MNP or the unfortified carrier added just before consumption to a high-phytate maize porridge 5 d/wk for 23 wk; primary outcomes were iron and zinc status and a secondary outcome was somatic growth. Compared with the control, the MNP increased serum ferritin (P < 0.05), body iron stores (P < 0.01) and weight-for-age Z-scores (P < 0.05) and decreased transferrin receptor (P < 0.05). The prevalence of iron deficiency fell by 30.6% (P < 0.01) and the prevalence of zinc deficiency decreased by 11.8% (P < 0.05). Absorption of iron from the MNP was estimated to be 7-8%. Inclusion of an exogenous phytase combined with NaFeEDTA and AA may allow a substantial reduction in the iron dose from existing MNP while still delivering adequate iron and zinc. In addition, the MNP is likely to enhance absorption of the high native iron content of complementary foods based on cereals and/or legumes.

Total iron and heme iron content and their distribution in beef meat and viscera

To determine the content of total iron (TFe) and heme iron (HeFe) in major cuts of meat and principal viscera of bovine origin. 55Fe (30 mCi) was injected into two 4-month-old calves. Triplicate samples of the 12 basic American cuts of meat and major viscera were obtained from each specimen. Samples were acid digested and their iron content was read by atomic absorption spectrophotometry. Duplicate samples of the basic cuts of meat and major viscera were analyzed to determine the concentration of 55Fe using a double isotopic technique. The mean and standard deviation of TFe for all cuts was 1.4 ± 0.3 mg/100 g of meat. The mean TFe for organs was (per mg/100 g): 0.9 ± 0.1 brain, 3.0 ± 0.05 kidney, 3.2 ± 0.04 heart, 5.7 ± 0.2 lung, 6.0 ± 0.1 liver, and 31.2 ± 0.4 spleen. HeFe was 64% of TFe in meat and 72.8% in spleen, 53.8% in lung, 35.7% in brain, 35.0% in kidney, 27.3% in heart, and only 13.6% in liver. Blood contained 85.5% of the radioisotope and only 1.4% was found in muscle and 1.6% was found in viscera. Results suggest that bovine cuts of meat have a low variation in TFe and that HeFe comprises more than 60% of TFe.

Iron bioavailability of rats fed liver, lentil, spinach and their mixtures

To study the effects of dietary iron source (basal diet-FeSO4 x 7H2O, liver, lentil, spinach, liver + lentil, liver+spinach and lentil+spinach) on iron bioavailability, fifty-six Albino Sprague Dawley derived male 21 days old rats were fed on iron-deficient diet (7.8 mg Fe kg(-1) diet) and the mentioned seven iron containing diets (40 mg Fe kg(-1) diet) for 10 days. Rats fed liver diet showed higher iron apparent absorption (52.1%), hemoglobin (Hb) gain (0.94 g/100 mL), Hb-iron gain (1.2 mg), Hb-regeneration efficiency (HRE%) (50.8%), relative efficiency of HRE% (106.5%), packed cell volume gain (2.22%) and mean corpuscular hemoglobin concentration (0.64 g dL(-1)). Liver resulted in an increase in these parameters when mixed with lentil and spinach diets. However, rats fed iron free diet showed the higher dry matter absorption.

Extrinsic labeling method may not accurately measure Fe absorption from cooked pinto beans (Phaseolus vulgaris): comparison of extrinsic and intrinsic labeling of beans

Isotopic labeling of food has been widely used for the measurement of Fe absorption in determining requirements and evaluating the factors involved in Fe bioavailability. An extrinsic labeling technique will not accurately predict the total Fe absorption from foods unless complete isotopic exchange takes place between an extrinsically added isotope label and the intrinsic Fe of the food. We examined isotopic exchange in the case of both white beans and colored beans (Phaseolus vulgaris) with an in vitro digestion model. There are significant differences in (58)Fe/(56)Fe ratios between the sample digest supernatant and the pellet of extrinsically labeled pinto bean. The white bean digest shows significantly better equilibration of the extrinsic (58)Fe with the intrinsic (56)Fe. In contrast to the extrinsically labeled samples, both white and red beans labeled intrinsically with (58)Fe demonstrated consistent ratios of (58)Fe/(56)Fe in the bean meal, digest, supernatant, and pellet. It is possible that the polyphenolics in the bean seed coat may bind Fe and thus interfere with extrinsic labeling of the bean meals. These observations raise questions on the accuracy of studies that used extrinsic tags to measure Fe absorption from beans. Intrinsic labeling appears necessary to accurately measure Fe bioavailability from beans.

Ferritin-iron is released during boiling and in vitro gastric digestion

Biofortification of staple foods with iron in the form of ferritin-iron is a promising approach to fighting iron-deficiency anemia in developing countries. However, contradictory results regarding iron bioavailability to humans from ferritin are not yet fully clarified. Furthermore, the question has been raised whether ferritin can potentially survive gastric passage intact and be absorbed via a ferritin-specific uptake mechanism. We studied changes of ferritin-iron and protein during cooking and in vitro gastric digestion. Water soluble, native ferritin-iron, measured in different legumes, represented 18% (soybeans) up to maximally 42% (peas) of total seed iron. Ferritin-iron was no longer detectable after boiling the legumes for 50 min in excess water. When the same cooking treatment was applied to recombinant bean ferritin propagated in Escherichia coli, some ferritin-iron remained measurable. During in vitro gastric digestion of recombinant bean ferritin and red kidney bean extract, ferritin-iron was fully released from the protein and dissolved at pH 2. Stability tests at varying pH at 37 degrees C showed that the release of ferritin-iron starts at pH 5 and is complete at pH 2. We concluded that ferritin-iron is efficiently released from the ferritin molecule during cooking and at gastric pH and that it should be absorbed as efficiently as all other nonheme iron in food.

Iron bioavailability from maize and beans: a comparison of human measurements with Caco-2 cell and algorithm predictions

BACKGROUND

An in vitro digestion and Caco-2 cell model may predict iron bioavailability to humans; however, direct comparisons are lacking.

OBJECTIVE

The objective was to test the differences in iron bioavailability between 2 maize varieties and 2 bean varieties (white beans and colored beans) by comparing human, Caco-2, and algorithm results.

DESIGN

Two randomized, 2 x 2 factorial experiments compared women's iron absorption from 2 maize varieties (ACR and TZB; n = 26) and 2 bean varieties (great northern and pinto; n = 13), each fed with and without ascorbic acid (AA) from orange juice. Nonheme iron bioavailability was determined from 2-wk retention of extrinsic radioiron tracers and was compared with Caco-2 cell and algorithm results from identical meals.

RESULTS

Without AA supplementation, women absorbed only about 2% of the iron from the maize or bean meals. The results were unaffected by the variety of either maize or beans. Adding AA (15-20 molar ratios of AA:iron) roughly tripled the iron absorption (P < 0.0001) from all test meals. Although the Caco-2 model predicted a slightly improved bioavailability of iron from ACR maize than from TZB maize (P < 0.05), it accurately predicted relative iron absorption from the maize meals. However, the Caco-2 model inaccurately predicted both a considerable difference between bean varieties (P < 0.0001) and a strong interaction between bean varieties and enhancement by AA (P < 0.0001). The algorithm method was more qualitatively than quantitatively useful and requires further development to accurately predict the influence of polyphenols on iron absorption.

CONCLUSIONS

Caco-2 predictions confirmed human iron absorption results for maize meals but not for bean meals, and algorithm predictions were only qualitatively predictive.

Oxalic acid does not influence nonhaem iron absorption in humans: a comparison of kale and spinach meals

OBJECTIVE

To evaluate the influence of oxalic acid (OA) on nonhaem iron absorption in humans.

DESIGN

Two randomized crossover stable iron isotope absorption studies.

SETTING

Zurich, Switzerland.

SUBJECTS

Sixteen apparently healthy women (18-45 years, <60 kg body weight), recruited by poster advertizing from the staff and student populations of the ETH, University and University Hospital of Zurich, Switzerland. Thirteen subjects completed both studies.

METHODS

Iron absorption was measured based on erythrocyte incorporation of (57)Fe or (58)Fe 14 days after the administration of labelled meals. In study I, test meals consisted of two wheat bread rolls (100 g) and either 150 g spinach with a native OA content of 1.27 g (reference meal) or 150 g kale with a native OA content of 0.01 g. In study II, 150 g kale given with a potassium oxalate drink to obtain a total OA content of 1.27 g was compared to the spinach meal.

RESULTS

After normalization for the spinach reference meal absorption, geometric mean iron absorption from wheat bread rolls with kale (10.7%) did not differ significantly from wheat rolls with kale plus 1.26 g OA added as potassium oxalate (11.5%, P=0.86). Spinach was significantly higher in calcium and polyphenols than kale and absorption from the spinach meal was 24% lower compared to the kale meal without added OA, but the difference did not reach statistical significance (P>0.16).

CONCLUSION

Potassium oxalate did not influence iron absorption in humans from a kale meal and our findings strongly suggest that OA in fruits and vegetables is of minor relevance in iron nutrition.

Phytate degradation determines the effect of industrial processing and home cooking on iron absorption from cereal-based foods

The aim of the present study was to compare Fe absorption from industrially-manufactured and home-cooked cereal foods. Fe absorption was measured using the radiolabelled Fe extrinsic tag technique in thirty-nine adult human subjects from cereal porridges manufactured by extrusion cooking or roller-drying, and from the same cereal flours after home cooking to produce pancakes, chappattis or bread. One series of cereal porridges was amylase-treated in addition before roller-drying. Fe absorption was relatively low from all products, ranging from 1·8–5·5% for rice, 2·5–3·5% for maize, 4·9–13·6 % for low-extraction wheat, and <1% for high-extraction wheat foods. The phytic acid content remained high after drying of the cereal porridges being about 1·20, 1·70, 3·20, 3·30 mg/g in low-extraction wheat, rice, high-extraction wheat and maize products respectively, and could explain the low Fe absorption. There were little or no differences in Fe absorption between the extruded and roller-dried cereals, although amylase pre-treatment increased Fe absorption from the roller-dried rice cereal 3-fold. This was not due to phytate degradation but possibly because of the more liquid nature of the cereal meal as fed. There were similarly few or no differences in Fe absorption between the industrially-processed cereals and home-cooked cereals made into pancakes or chappattis. Bread-making, however, degraded phytic acid to zero in the low-extraction wheat flour and Fe absorption increased to 13·6%, the greatest from all cereal foods tested. It is concluded that Fe absorption from extruded, roller-dried or home-cooked cereal foods is similarly low and that only those cooking procedures such as bread-making, which extensively degrades phytic acid, or amylase pre-treatment, which substantially liquifies cereal porridges, improve Fe absorption.

Comparison of urinary monitoring, faecal monitoring and erythrocyte analysis of stable isotope labels to determine magnesium absorption in human subjects

We have evaluated urinary monitoring and erythrocyte analysis to determine Mg absorption in human subjects as alternatives to the conventional technique of faecal monitoring by stable-isotope techniques. Ten healthy adults received 2·2 mmol 25Mg in water, together with wheat bread, followed 15 min later by intravenous injection of 0·6 mmol 26Mg (day 1). Brilliant blue and Yb (given on day 0 and day 1 respectively) served as qualitative and quantitative faecal markers. Urine was collected for 6 d after test meal intake. Complete collections of faeces were made until excretion of the second brilliant blue marker (given on day 7). Mg isotope ratios were determined by thermal ionisation-MS in urine and faeces and by inductively coupled plasma-MS in erythrocytes. Absorption was determined based on: (1) 6 d urine pools; (2) 24 h urine pools (collected 22–46 h after test meal intake); (3) erythrocytes from a blood sample drawn on day 14; (4) complete 6 d faecal pools; (5) faecal pools based on the first three consecutive stools after excretion of the first brilliant blue marker. Differences in mean Mg absorption (42 44 %) were statistically insignificant between techniques, except when based on 6 d urine pools for which the value was significantly lower (33 (sd 7) %, P=0·0003, ANOVA). The results indicate that Mg absorption can be determined from 24 h urine pools or erythrocytes obtained 14 d after test meal intake, an alternative method to the more time-consuming and labour-intense faecal monitoring. The choice of technique depends on practical and financial considerations.

An evaluation of EDTA compounds for iron fortification of cereal-based foods

Fe absorption was measured in adult human subjects consuming different cereal foods fortified with radiolabelled FeSO4, ferrous fumarate or NaFeEDTA, or with radiolabelled FeSO4or ferric pyrophosphate in combination with different concentrations of Na2EDTA. Mean Fe absorption from wheat, wheat–soyabean and quinoa (Chenopodium quinoa) infant cereals fortified with FeSO4or ferrous fumarate ranged from 0·6 to 2·2 %. For each infant cereal, mean Fe absorption from ferrous fumarate was similar to that from FeSO4(absorption ratio 0·91–1·28). Mean Fe absorption from FeSO4-fortified bread rolls was 1·0 % when made from high-extraction wheat flour and 5·7 % when made from low-extraction wheat flour. Fe absorption from infant cereals and bread rolls fortified with NaFeEDTA was 1·9–3·9 times greater than when the same product was fortified with FeSO4. Both high phytate content and consumption of tea decreased Fe absorption from the NaFeEDTA-fortified rolls. When Na2EDTA up to a 1:1 molar ratio (EDTA:Fe) was added to FeSO4-fortified wheat cereal and wheat–soyabean cereal mean Fe absorption from the wheat cereal increased from 1·0 % to a maximum of 5·7 % at a molar ratio of 0·67:1, and from the wheat–soyabean cereal from 0·7 % to a maximum of 2·9 % at a molar ratio of 1:1. Adding Na2EDTA to ferric pyrophosphate-fortified wheat cereal did not significantly increase absorption (P>0·05). We conclude that Fe absorption is higher from cereal foods fortified with NaFeEDTA than when fortified with FeSO4or ferrous fumarate, and that Na2EDTA can be added to cereal foods to enhance absorption of soluble Fe-fortification compounds such as FeSO4.

Animal- and plant-food-based diets and iron status: benefits and costs

Fe seems to be the only nutrient deficiency that industrialized and low-income countries have in common. Thus, Fe is one of the most critical nutrition requirements to be met in most diets in human subjects. Fe deficiency is caused not only by too low an intake, but is also the result of low bioavailability, as well as an increased Fe requirement due to physiological variables or clinical problems which are not met by an increased dietary intake of Fe. In low-income countries poor dietary quality rather than Fe intake seems to be the key determinant of impaired Fe status. Sometimes the Fe intake even exceeds that in populations of industrialized countries. The interaction of all enhancers (e.g. ascorbic acid and meat), as well as inhibitors (such as bran, polyphenols, egg yolk, soyabean products, Ca, Ca3(PO4)2 and phytic acid (or phytate)) is what determines the bioavailability of non-haem-Fe in the meal. Dietary composition seems to be particularly important when Fe reserves are low, or in the presence of Fe deficiency. Furthermore, the development of anaemia as a result of Fe deficiency, secondary to Fe-stress situations, is dependent on the Fe balance in the host. With respect to the dietary intake of Fe, other products in the food consumed as well as previous treatment of the product (e.g. heat treatment and processing) may also influence bioavailability. Despite all efforts to counteract Fe deficiency it still represents one of the dominant problems in the micronutrient sphere. It is apparent that there is no simple solution to the problem, and the fact that Fe deficiency still occurs in affluent societies consuming a mixed diet speaks for itself; a more holistic view of total dietary composition and the role of enhancers and inhibitors is needed.

Effects of dietary iron reduction versus phlebotomy in patients with chronic hepatitis C: results from a randomized, controlled trial on 40 Japanese patients

BACKGROUND AND AIM

Iron may play an important role in the pathogenesis of hepatitis C. We conducted this randomized, controlled trial comparing phlebotomy with dietary iron reduction.

METHODS

Forty patients with chronic hepatitis C showing serum ferritin levels of over 150 ng/ml were randomized to either group A (low-iron diet for six months) or group B (phlebotomy biweekly). Phlebotomy was continued until serum ferritin had reached 20 ng/ml or less.

RESULTS

At enrollment the clinical characteristics of patients in the two groups were similar. Serum ALT levels were significantly reduced in both groups, but the percent change in alanine aminotransferase (ALT) was larger in group B (median, -47.1 [range, -69.1 to -16.7] %) than in group A (-24.2 [-72.6 to 15.9] %, p<0.001). In group A subjects, no correlation was detected between percent change in ALT and clinical parameters. In group B subjects, the baseline ALT activity was significantly correlated with percent change in ALT (p<0.05), but iron-related parameters were not correlated.

CONCLUSION

The efficacy of phlebotomy is superior to that of dietary iron reduction in chronic hepatitis C. Serum levels of transaminase activities were a better indicator for phlebotomy than conventional indices of iron overload.

Meat protein fractions enhance nonheme iron absorption in humans

The nature of the enhancing effect of muscle tissue on nonheme iron absorption in humans is unclear but thought to be related to muscle proteins. We conducted radioiron absorption studies to compare iron absorption from proteins isolated from beef and chicken muscle with that from freeze-dried beef and chicken muscle and from egg albumin. All meals contained an equivalent amount of protein as part of a semisynthetic liquid formula. Freeze-dried beef and chicken muscle increased iron absorption 180% (P < 0.001) and 100% (P < 0.001), respectively, relative to egg albumin. When added to the meal at an equivalent protein level (15 g), the isolated beef protein and the isolated heme-free beef protein with 94 and 98% protein content, respectively, increased iron absorption to the same extent as the native beef muscle. Similarly, when added to the meal at an equivalent protein level (30 g), isolated chicken muscle protein (94% protein) increased iron absorption similarly to native chicken muscle. Iron absorption from the meal containing the isolated heme-free chicken protein, however, was 120% (P < 0.01) greater than from the meal containing freeze-dried chicken muscle, indicating that a nonprotein component of muscle tissue with iron-binding potential may have been removed or concentrated by the protein extraction and separation procedures. Our results support the hypothesis that the enhancing effect of muscle tissue on iron absorption is mainly protein related but indicate that other factors may also play a role.

Serum iron curves can be used to estimate dietary iron bioavailability in humans

Erythrocyte incorporation of isotopic iron (Fe) is the standard method for assessing iron bioavailability, but the process is expensive, technically difficult, and gives no information on the kinetics of absorption. The main objective of this study was to validate serum Fe curves as measures of dietary iron absorption because previous work demonstrated that serum iron curves can be generated with iron doses as low as 5-20 mg and that up to 20 mg iron can be added to meals without affecting relative absorption. In 3 studies, groups (n = 10, 10, 21) of Fe-deficient, mildly anemic women consumed meals of varying calculated Fe bioavailability, with and without added ferric chloride (10 mg Fe). Blood samples were collected at baseline and every 30 min for 4 h after the meal. Serum Fe concentrations were measured. Areas under the serum Fe curves and peak concentrations were used in different models to estimate Fe absorption and uptake. In 21 subjects, (58)Fe-enriched ferric chloride was added to the meals, and blood was taken 2 wk later to calculate red cell isotope incorporation. The addition of 10 mg Fe to test meals produced measurable serum iron curves even when the meal Fe bioavailability was low. Serum Fe curves were highly reproducible and were affected as expected by food composition. Even the single measurement at the estimated time of peak iron concentration was correlated significantly with erythrocyte incorporation of (58)Fe (r = 0.72, P < 0.0001). Hence the extent and rate of absorption of nonheme iron from meals, rather than in individuals, can be investigated with such subjects without the need for isotopes.

Meat consumption in a varied diet marginally influences nonheme iron absorption in normal individuals

It is widely recognized that the intake of animal foods is the most important dietary determinant of the iron status of a population. The primary reason is the high bioavailability of heme iron, but it is also known from radiolabeled single-meal feeding studies in humans that muscle tissue facilitates absorption of nonheme iron. In the present study, we examined the effect of meat intake on nonheme iron absorption from a whole diet. Iron absorption was measured during 3 separate dietary periods in 14 volunteers (7 men and 7 women) by having them ingest a radioiron-labeled wheat roll with every meal for 5 d. The diet was freely chosen for the first dietary period and altered to eliminate or maximally increase the intake of muscle foods during the second and third periods. Nonheme iron absorption did not differ for the 3 dietary periods although the geometric mean of 4.81% when subjects consumed a freely chosen diet increased by 35% to 6.47% with maximum meat consumption (P = 0.075). When nonheme absorption was adjusted to normalize for differences in iron status using serum ferritin correction and the 3 absorption periods were pooled, multiple regression analysis indicated no significant relation with heme or nonheme iron, vitamin C, calcium, phosphorus, fiber, or tea content of the diet with the exception of animal tissue (P = 0.013). We conclude that the higher iron status associated with the consumption of an omnivorous diet is due more to the intake of heme iron than to the enhancing effect on nonheme iron absorption.