Iron metabolism and prevention of iron deficiency via iron fortification of foods

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1 Trace Elements and Electrolytes, Vol. No. /2013 (1-11) Iron metabolism and prevention of iron deficiency via iron fortification of foods Anna Eisenstadt 1, Ulrich Schäfer 1, Michael Glei 2 and Gerhard Jahreis 1 Original 2013 Dustri-Verlag Dr. K. Feistle ISSN Department of Nutritional Physiology, 2 Department of Nutritional Toxicology, Institute of Nutrition, Friedrich Schiller University, Jena, Germany DOI /TEX01303 e-pub: month, day, year Key words iron absorption iron bioavailability iron deficiency iron fortification serum ferritin transferrin receptor Accepted for publication March 12, 2013 Correspondence to Prof. Dr. Gerhard Jahreis Institute of Nutrition, Friedrich Schiller University, Dornburger Str. 24, Jena, Germany b6jage@uni-jena.de Abstract. Introduction: Nutritional iron deficiency can be caused by low dietary iron bioavailability. The provision of foods fortified with iron might be a feasible strategy against nutritional iron deficiency in areas where its prevalence is high. However, the selection of an optimal combination of a food vehicle and an iron fortificant is challenging. The iron fortificant should be sufficiently bioavailable and should not adversely affect sensory properties of the fortified food. Methods: Literature research was performed to identify such combinations from 22 efficacy and effectiveness studies evaluating iron fortification of foods. Results and discussion: In the selected studies, frequently used iron fortificants were NaFeEDTA, ferrous sulfate, and micronized ferric pyrophosphate. Cereal-based products, salt, sauces, fruit juice, and cow s milk-based foods were used as food vehicles. It is believed that native dietary iron and fortification iron do not pose a risk of iron overload due to a tight regulation of iron absorption in normal subjects. However, iron intake exceeding iron requirements might lead to increased risk of cardiovascular diseases and colorectal cancer. Conclusions: Regular intake of iron-fortified foods is effective in curing nutritional iron deficiency. Such interventions should be targeted at people with low iron status who fail to improve their iron deficiency by means of dietary modification. Introduction Iron deficiency (ID) is the most common nutrition-related disorder in the world [1]. Low bioavailability of dietary iron and low amounts of iron in the diet can cause nutritional ID, wherein low dietary iron bioavailability is the major factor [2]. Dietary iron bioavailability indicates the amount of dietary iron that can be absorbed and utilized by the body [3]. A typical European diet contains sufficient amounts of meat, fruits, and vegetables and has an iron bioavailability of ~ 15% in borderline iron-deficient subjects [4]. Depending on the composition of Western-type vegetarian diets, their iron bioavailability varies from 5 to 12% [5]. Monotonous plant-based diets consumed in many developing countries have low iron bioavailability (1 9%) due to low amounts of meat and ascorbic acid-rich foods and high amounts of inhibitors of non-heme iron absorption [1, 6]. Food fortification with iron is one of the approaches to correct or prevent ID. When the risk of ID affects the majority of a population, mass fortification programs can be appropriate. If only a minority of the population is affected, fortification programs targeted at risk groups for ID can be considered to avoid excessive iron intake in the majority of the population. However, the selection of an optimal combination of a food vehicle and an iron fortificant is challenging. The pattern of food consumption, sensory properties of the fortified food, and the bioavailability of the iron fortificant play an important role in this process. Efficacy and effectiveness studies are used to evaluate the impact of food fortification programs [1, 2]. Also, they provide information regarding vehicle and/or fortificant combinations that are currently considered suitable for iron fortification programs worldwide. The combinations that may be of interest for industrialized countries were selected from such studies. In addition, this work provides an overview of the current knowledge about iron absorption and iron bioavailability. Intestinal iron absorption Dietary iron is absorbed by mature enterocytes of the duodenum and proximal

2 Eisenstadt, Schäfer, Glei and Jahreis 2 Figure 1. Intestinal iron absorption (modified from [7, 8]). The heme carrier protein 1 (HCP1) imports intact heme. Fe 2+ is released from heme by the heme oxygenase (HO). The divalent metal ion transporter 1 (DMT1) imports the Fe 2+ form of non-heme iron. In order to be taken up, the Fe 3+ form must be reduced to Fe 2+ by the duodenal cytochrome B (DCYTB) or by ascorbic acid. After entering the intracellular iron pool in the enterocyte, iron can be either stored bound to ferritin or exported into the circulation via ferroportin 1 (FPN1). Presumably, the poly (rc)-binding protein (PCBP1) delivers Fe 2+ to ferritin. jejunum. Heme and non-heme iron have distinct absorption pathways (Figure 1). Heme (ferrous (Fe 2+ ) protoporphyrin IX) is contained in hemoglobin and myoglobin of animal-based foods. All other forms of dietary iron are referred to as non-heme or inorganic iron. Most native non-heme iron (Fe 2+ or ferric (Fe 3+ )) is complexed with organic acids or peptides. Also, it includes Fe 2+ or Fe 3+ salts. Fe 3+ is the stable form of iron in most of its biological complexes and the predominant form of dietary iron [7, 8]. Non-heme iron can be added to foods in form of Fe 2+ and Fe 3+ salts, elemental iron, and chelated iron [1, 9]. In Western countries, fortification iron can be contained in infant formulas, complementary foods, and breakfast cereals. Presumably, intact heme binds to the heme carrier protein 1 (HCP1), and this complex undergoes endocytosis. Heme oxygenase (HO) catalyzes the degradation of heme, and the released Fe 2+ enters the intracellular iron pool in the enterocyte [8, 10]. The Fe 2+ form of non-heme iron is imported into the enterocyte via the divalent metal ion transporter 1 (DMT1) using the energy provided by the H + electrochemical gradient. Fe 3+ must be reduced either by ferrireductases, including the duodenal cytochrome B (DCYTB), or reducing substances, such as ascorbic acid [7, 8]. Iron can be stored in the enterocyte bound to the protein ferritin. This iron can be lost after 2 3 days because of the exfoliation of the enterocyte. The poly (rc)-binding protein 1 (PCBP1) might be the metallochaperon that delivers Fe 2+ to ferritin. The release of iron into the circulation is mediated by the iron exporter ferroportin 1 (FPN1) [8, 10]. The ferroxidase hephaestin might be the electron acceptor that converts Fe 2+ into Fe 3+ before the released iron binds to the plasma protein transferrin [7, 11]. The binding of the hormone hepcidin to its receptor FPN1 inhibits iron export by causing the internalization and the degradation of both molecules [8]. Because humans lack mechanisms for active excretion of iron, a tight regulation of intestinal iron absorption is essential for iron homeostasis [11]. Iron absorption is controlled both on the systemic and local level. On the systemic level, the liver regulates the release of dietary iron from the enterocytes into the circulation by producing the hormone hepcidin. Hepcidin synthesis is affected by iron stores, the rate of erythropoiesis, hypoxia, and inflammation [8]. On the local level, iron uptake into the enterocytes is affected by the intracellular concentration of iron and oxygen [10]. The interaction of iron regulatory proteins (IRPs) and iron-responsive elements (IREs) regulates post-transcriptionally

3 Iron metabolism and prevention of iron deficiency via iron fortification of foods 3 the expression of several genes whose products are important for iron metabolism. The IREs are located in the messenger RNA of FPN1, ferritin, DMT1, and transferrin receptor 1 (TfR 1). Both FPN1 and DMT1 have IRE and non-ire transcripts [11]. Hypoxia affects the transcription of FPN1, DCYTB, HO-1, DMT1, and TfR 1. Intracellular heme accumulation stimulates FPN1, ferritin, and HO-1 transcription [10]. Heme iron and its bioavailability Western diets provide 10 15% of total iron as heme iron. It comprises ~ 40% of total iron in animal tissues, and can be transformed into non-heme iron during storage or because of high cooking temperature. Depending on iron status and food composition, heme iron absorption ranges between 15 and 35%. It is comparatively well absorbed because heme is soluble under the conditions of the small intestine and because of the specific uptake mechanism [12, 13]. Heme iron absorption can be enhanced by an unidentified factor in meat and inhibited by calcium [3]. Increased intake of heme iron rather than the enhancement of non-heme iron absorption is responsible for the higher iron status in omnivores. Food fortification with heme in the form of hemoglobin from dried animal red blood cells is technically difficult and leads to sensory changes in the food vehicle [2, 9]. Non-heme iron and its bioavailability Non-heme iron is the predominant form of dietary iron. Depending on iron status and food matrix, non-heme iron absorption can be as low as 2% or as high as 20%. These two factors have a greater influence on nonheme iron absorption than on heme iron absorption. Non-heme iron can be absorbed if it is ionizable or soluble in the small intestine. It is assumed that the Fe 2+ form of nonheme iron is better absorbed than the Fe 3+ form. In the absence of sufficient amounts of solubilizing agents, Fe 3+ is poorly absorbed because a ph > 1 favors a rapid formation of Fe 3+ hydroxides. Fe 2+ hydroxides can be formed at a higher ph, namely > 7 [12]. Dietary factors with enhancing effect on nonheme iron absorption include ascorbic acid, meat, and the food additive EDTA. Phytate, calcium, and polyphenols inhibit non-heme iron absorption. Possible mechanisms responsible for the enhancing effect are the reduction of Fe 3+, the formation of soluble iron ligand complexes, the stimulation of gastric acid secretion, and the modulation of gene expression. Possible inhibiting mechanisms are the formation of insoluble iron ligand complexes, the inhibition of iron transport, and the modulation of gene expression [2, 3, 10]. The concept of a common non-heme iron pool, i.e., the pool of absorbable nonheme iron in the intestine, deals with the effect of dietary constituents on non-heme iron absorption and the bioavailability of iron fortificants. Fortification iron that is soluble in the gastric juice enters the common non-heme iron pool and is absorbed to the same extent as native non-heme iron [2]. The relative bioavailability value (RBV) is used to describe the bioavailability of fortification iron. This value expresses the absorbability of an iron fortificant relative to that of ferrous sulfate. The bioavailability of fortification iron can be increased through particle size reduction, the addition of organic acids or EDTA compounds, and dephytinization. However, the enhancing effect on iron absorption of ascorbic acid and sodium EDTA does not apply to all types of fortification iron. Watersoluble iron compounds (e.g., ferrous sulfate) are highly soluble in the gastric juice and enter the common non-heme iron pool completely. Their bioavailability is high, but they often cause organoleptic problems in the food vehicle [1]. Iron compounds that are poorly water-soluble and soluble in diluted HCl (e.g., ferrous fumarate) also easily enter the common non-heme iron pool and are well absorbed. They cause fewer organoleptic problems than the water-soluble iron compounds [2, 9]. Iron fortificants that are insoluble in water and poorly soluble in diluted HCl (e.g., elemental iron powders) are characterized by low absorption because of incomplete dissolution in the gastric juice. They have only marginal effect on the organoleptic properties of foods and are preferred by the food industry [1]. The rate and extent

4 Eisenstadt, Schäfer, Glei and Jahreis 4 of oxidation of elemental iron powders determine their dissolution in the gastric juice. NaFeEDTA and ferrous bisglycinate represent chelate compounds. In foods containing high amounts of inhibitors of iron absorption, iron absorption from these fortificants is higher than that from ferrous sulfate [1, 9]. Measurements of serum ferritin (SF) and serum transferrin receptor (stfr) concentrations are considered to be the best approach to assess the iron status of populations. Additionally, the measurement of hemoglobin (Hb) concentration in blood provides information about the prevalence of anemia, an important health indicator. Normal iron status implies optimal Hb concentration, adequate tissue iron supply, and the presence of storage iron [5]. Storage iron is contained mainly in hepatocytes and comprises 20% of body iron. In an iron-replete body, it can also be contained in macrophages of the reticuloendothelial system. Storage iron is bound to the intracellular proteins ferritin and hemosiderin, whereas ferritin-bound iron can be easily mobilized [11]. SF indicates the relative extent of iron stores because its concentration is directly proportional to iron stores, with 1 µg/l SF corresponding to 8 10 mg storage iron. ID is defined by the absence of storage iron with or without anemia and is indicated by SF < 15 µg/l for males and females (> 5 years) [14]. Low SF levels are very specific for ID, but increased SF levels can be associated with various factors including acute and chronic inflammation and increased alcohol consumption. Increased stfr concentration indicates enhanced erythropoiesis and tissue ID independently of inflammation [13]. Infants, young children, adolescents, and women of reproductive age are at risk of developing ID. In European countries, the prevalence of ID among infants and toddlers ranges from 2 to 48% and that among menstruating women ranges from 4 to 33% [15]. The prevalence of anemia among the risk groups for ID is highest in Africa and Southeast Asia. The main symptom of ID is chronic fatigue. ID impairs cognitive performance of children and physical capacity of adolescents and adults. ID in pregnancy is associated with increased rates of maternal mortality, prematurity, and infant loss [14]. However, the incidence of ID anemia is similar between subjects consuming a well-balanced vegetarian diet and omnivores. Normal iron status and iron deficiency Iron absorption in relation to iron status Iron cannot be actively excreted, but its absorption can be downregulated by the hormone hepcidin. Normally, iron absorption is upregulated in individuals with low iron status and downregulated in iron-replete individuals [11, 16]. Iron status has the greatest impact on iron absorption [3]. Factors affecting iron absorption should be studied in subjects with low iron status rather than in iron-replete subjects because the amount of absorbed iron is almost the same in iron-replete subjects given diets of different iron bioavailability. There is a good inverse relationship between total dietary iron absorption and SF concentration < 60 µg/l. In subjects with higher SF levels, iron absorption equals iron losses/requirements. In this situation, the regulation of iron absorption maintains iron balance/steady state, in which the amount of iron in the body remains constant. This prevents excessive accumulation of iron in normal iron-replete subjects consuming a diet of high iron bioavailability or containing iron-fortified foods [16]. However, this control mechanism is valid for iron ingested with foods but not for iron taken in as supplements. After the introduction of dietary modifications, depleted iron stores reach 80% of the final amount during the first year as assessed by SF concentration. Then their growth is slower, and the steady state is attained 1 2 years later. The final size of iron stores depends on iron losses, dietary iron intake and bioavailability. A change in these factors, e.g., when women enter menopause, leads to a new iron balance [17]. The Dietary Iron Requirements proposed by the Scientific Committee for Food of the European Community and the Dietary Reference Intakes for iron proposed by the US Institute of Medicine are based on dietary iron

5 Iron metabolism and prevention of iron deficiency via iron fortification of foods 5 Table 1. Selected efficacy and effectiveness studies with iron-fortified foods. Food vehicle Iodized salt (IS) Rice Cow s milk-based foods Fruit juice Design; participants (age, iron status as inclusion criteria) RCT a ; & (5 15 years, Hb 80 g/l, SF < 15 µg/l or stfr > 7.6 mg/l) RCT; & (5 15 years, Hb 80 g/l, SF < 15 µg/l or stfr > 7.6 mg/l) multicenter trial; & ( 10 years) RCT; & (5 15 years, Hb 80 g/l, SF < 30 µg/l or stfr > 8.5 mg/l) RCT; & (6 15 years) RCT; & (6 15 years) RCT; & (5 11 years, Hb 70 g/l) RCT; (18 49 years, Hb g/l) RCT; & (6 13 years, SF < 20 µg/l or stfr > 7.2 mg/l) RCT; & (12 30 months) RCT; & (6 months) RCT; (18 35 years, Hb 110 g/l, SF < 40 µg/l) Amount of iron-fortified food/d; amount of fortification iron/d (ad libitum) 6.1 g IS/d b with 12.2 mg iron/d as micronized ferric pyrophosphate (MFP) (mean particle size 2.5 µm) Country; duration; impact; reference India; 10 mo; + c ; [34] (ad libitum) 6.1 g IS/d b with 12.2 mg iron/d as India; 10 mo; +; [34] encapsulated ferrous fumarate d (ad libitum) 10 g IS/d with 10 mg iron/d as India; 12 mo; +; [33] chelated ferrous sulfate e (ad libitum) g IS/d with mg Côte d Ivoire; 6 mo; +; [31] iron/d as MFP (mean particle size 2.5 µm) (ad libitum) 7 12 g IS/d with mg Morocco; 10 mo; +; [26] iron/d as MFP (mean particle size 2.5 µm) (ad libitum) 7 12 g IS/d with 7 12 mg Morocco; 10 mo; +; [25] iron/d as encapsulated ferrous sulfate f 125 g dry rice/d with 18.8 mg iron/d as MFP India; 8 mo; +; [42] (mean particle size 3.14 µm) 56 g dry rice/d g with 13 mg iron/d as MFP Mexico; 6 mo; +; [35] (mean particle size 0.3 µm, SunActive Fe ) 100 g dry rice/d with 20 mg iron/d as MFP India; 7 mo; +; [30] (mean particle size 2.5 µm) 44 g dry complementary food/d with 10 mg iron/d as ferrous gluconate or with 10 mg iron/d as ferrous sulfate (ad libitum) reconstituted follow-on formula milk with 1.2 mg iron/100 ml as ferrous sulfate Mexico; 6 mo; + (both fortificants); [37] United Kingdom; 12 mo; h ; [21] 500 ml fruit juice/d with 18 mg iron/d as encapsulated MFP i Spain; 4 mo; +; [41] a Randomized controlled trial. b The properties of the salt were adjusted during the trial (in the first 2 months: grain size 2 mm, moisture content 0.5%; in the remaining 8 months: grain size 1 mm, moisture content 1.8%). c The intervention had impact on the iron status of participants. d The encapsulated ferrous fumarate mix included ferrous fumarate, soy stearine, titanium dioxide, hydroxypropyl methylcellulose, and sodium hexametaphosphate (SHMP). e Ferrous sulfate was chelated with malic acid and SHMP. Sodium dihydrogen phosphate was added to enhance iron absorption. f Ferrous sulfate was encapsulated with partially hydrogenated vegetable oil. g The amount of rice per portion was adjusted during the trial, but the amount of fortification iron per portion was constant (in the first 3 months: 75 g rice/portion, in the remaining 3 months: 37 g rice/portion). h The intervention had no impact on the iron status of participants. i MFP was coated with lecithin. The mean particle size of MFP was not specified. bioavailability in borderline iron-deficient subjects and aim towards the maintenance of this iron status. Borderline ID is defined by SF of 15 µg/l and represents a stage between the iron-replete and iron-deficient state, where iron stores are absent. The state of borderline ID is considered normal because iron supply to tissues is adequate [4, 5, 13, 19]. Results of iron absorption studies with isotope-labeled meals are sometimes adjusted to the reference dose absorption of 40% or to the iron status close to borderline ID characterized by the presence of small iron stores (SF = 30 µg/l). First, iron absorption in subjects with varying iron status is measured both from the test meal and from the standard reference dose, namely 3 mg iron consumed in the fasting state as a solution containing radioiron-labeled ferrous sulfate and 30 mg ascorbic acid. Iron absorption from the reference dose correlates with the absorption of non-heme iron from meals. Second, iron absorption from meals is adjusted to the reference dose absorption in subjects with a certain iron status. The reference dose absorption of 40% is representative for subjects with SF of 30 µg/l and 60% for subjects with SF of 15 µg/l [19, 20]. Methods Efficacy and effectiveness studies were identified through the PubMed search engine ( The search was performed using iron fortification and iron fortified as key words. Filters were set at January 1992 to May 2012, clinical trial, human, and English.

6 Eisenstadt, Schäfer, Glei and Jahreis 6 Selection criteria Eligible trials should be designed as placebo-controlled long-term intervention trials. The difference in the treatment of experimental and control groups should not lie in multiple micronutrients. Study population could belong to any age/gender group, with the exception of infants < 6 months of age and pregnant women. The participants could be iron-deficient or not. Studies had to contain measurements of Hb, SF, or stfr. Classification of studies Interventions that showed significantly (p-value at least 5% or the 95% CI) improved median or mean concentrations of at least one indicator of iron status (Hb, SF, stfr) in the treatment group compared to the control group had impact on the iron status of participants ( + ). Otherwise, the intervention had no impact on the iron status of participants ( ) (Table 1). Results and discussion Food vehicles employed in the 22 selected studies were wheat- or rice-based foods, salt, Asian sauces, sugar, fruit juice, and cow s milk-based products targeted at infants and toddlers [21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43]. Most frequently added iron compounds included ferrous sulfate (various types), NaFeEDTA, and micronized ferric pyrophosphate (MFP) (various types). The frequency of the consumption of the fortified food varied (daily, on school days, on working days) from trial to trial. Four interventions with iron-fortified foods had no impact on the iron status of participants [21, 38, 40, 43]. All other interventions with iron-fortified foods affected the iron status of participants, whereas Blanco-Rojo et al. [41] reported that the SF level of Spanish women with low iron stores increased significantly after 1 month of intervention with iron-fortified fruit juice. The intervention with chelated ferrous sulfate conducted by Vinodkumar et al. [33] was categorized as has impact based on the significantly improved Hb level. However, the effectiveness of their intervention in improving the iron status of participants is not convincing because Hb concentration was the only indicator measuring iron status, the group of participants was very heterogeneous (> 10 years), and the changes in the prevalence of anemia were not reported. In the effectiveness trial conducted by Wegmuller et al. [31] in Côte d Ivoire, the prevalence of malaria (55% among screened children) was high, and the dietary iron intake was reported to be sufficient. Under these circumstances, the provision of iron-fortified food to improve the iron status of a population is questionable. In this trial, stfr level and the prevalence of ID without anemia decreased significantly in the treatment group. The overall assessment of the impact of iron interventions on the iron status of participants has limitations. Besides the changes in the indicators of iron status, ideal assessment should also consider the iron status of participants at baseline, the duration of the interventions, and the change in the prevalence of ID. Characteristics of the 11 studies evaluating iron fortification of rice, salt, beverages, and cow s milk-based foods are summarized in Table 1. These food vehicles can be of interest for potential iron fortification programs in industrialized countries. If the average amount of the iron-fortified food consumed per person per day was specified in studies with the ad libitum intake, this amount was given in the table. Additional publications suggest that iron fortification of maizebased foods can reach a high proportion of the population in Central America, Mexico, and Eastern Africa. 78 countries worldwide have established or are planning to establish mandatory, voluntary, or targeted wheat flour fortification programs. Although wheat flour fortification is widespread, its effect on the reduction of the prevalence of ID seems to be marginal at the national level. This can be related to the use of iron fortificants with low bioavailability, such as atomized or H- reduced iron, and to low fortification levels. A review of current national wheat flour fortification programs as well as recommendations for wheat flour fortification with iron have been published recently [44, 45].

7 Iron metabolism and prevention of iron deficiency via iron fortification of foods 7 Salt Iron deficiency anemia affects iodine metabolism. Its treatment is likely to improve the efficacy of iodine prophylaxis. In the selected studies, iron fortificants employed for the fortification of iodized salt (IS) included MFP (mean particle size 2.5 µm), encapsulated ferrous sulfate or ferrous fumarate, and chelated ferrous sulfate. Evident improvement of the iron status of participants has been demonstrated in four trials [25, 26, 31, 34]. In trials with MFP-fortified salt (2 3 mg iron/g), almost one third of the interviewed households reported color changes in foods. However, the overall acceptability of the DFS was comparable to that of the IS [26, 31, 34]. In the effectiveness trial with encapsulated ferrous fumarate, DFS (1.8% moisture content, 2 mg iron/g) was described as dirty by the majority of the interviewed women, and color changes in foods containing the DFS were observed by 59% of the households receiving it. While dietary iron bioavailability was relatively high (10%), iron absorption from encapsulated ferrous fumarate (1.1%) and MFP (0.9%) estimated based on changes in iron stores were similarly low. Some participants were non-compliant in the encapsulated ferrous fumarate group [34]. Isotope studies indicate that the RBV of these fortificants is lower in subjects with poor iron status than in iron-replete subjects because of a stronger upregulation of iron absorption from ferrous sulfate in subjects with poor iron status. In other studies with MFP-fortified IS, dietary iron bioavailability was 2 4% or 14%, and estimated iron absorption from this compound was 2 or 3.5%, respectively [26, 31]. DFS containing encapsulated ferrous fumarate (1 mg iron/g) with the water-binding agent sodium hexametaphosphate (SHMP) was introduced in a school meal program in India. IS fortified with ferrous sulfate (1 mg iron/g) encapsulated with partially hydrogenated vegetable oil was used in a trial with Moroccan schoolchildren. During the rainy season, the development of yellow color in the DFS (3% moisture content) decreased its acceptability to households from 100% to 86% [25]. Wegmuller et al. [46] observed that the encapsulation of ferrous sulfate with seven different capsule materials, including partially hydrogenated soybean oil, did not prevent the development of unacceptable color changes in DFSs (0.18% or 1.55% moisture content, 1 mg iron/g), while the color of DFSs (0.18% or 1.55% moisture content) containing ferrous sulfate (1 mg iron/g salt) and SHMP was judged acceptable after 2 months of storage. According to Vinodkumar et al. [33], chelated ferrous sulfate-fortified salt (1 mg iron/g) has white color, high bioavailability, and does not cause color changes in cooked foods. Rice Both hot and cold extrusion was used to produce artificial iron-fortified rice grains in the selected efficacy studies. The use of various types of MFP resulted in iron-fortified rice that was highly acceptable to participants. Their iron status improved in all three interventions despite the low bioavailability of iron from MFP [30, 35, 42]. When non-encapsulated MFP (mean particle size 2.5 µm) is added via the hot extrusion method, the artificial rice grains are very similar to natural rice both in cooked and uncooked form. The addition of non-encapsulated MFP (mean particle size 3.14 µm) using the cold extrusion method, results in rice that is indistinguishable from natural rice in the cooked form. In the study with MFP with the mean particle size of 2.5 µm, estimated iron absorption from this compound was 2.1% [30, 42]. In an isotope absorption study with mostly iron-deficient adult women, iron absorption from MFP (SunActive Fe, 57 Fe-labeled experimental compound; mean particle size 0.77 µm)-fortified rice was 3% (24% RBV). Cow s milk-based foods The disadvantage of cow s milk as a food vehicle for iron fortification is low iron bioavailability due to the inhibitory effects of calcium and casein. Ferrous bisglycinate and encapsulated MFP can be used as iron fortificants for liquid milk. Both fortificants can be well absorbed when added to this vehicle, and ferrous bisglycinate does not cause lipid peroxidation. In the selected studies, foods targeted at infants and toddlers were based on

8 Eisenstadt, Schäfer, Glei and Jahreis 8 powdered cow s milk. In the trial with ferrous sulfate-fortified follow-on formula, Hb and SF of mostly Caucasian British infants were not affected by the intervention [21]. Ferrous gluconate produces less adverse sensory changes in powdered whole cow s milk than ferrous sulfate. In the study with Mexican toddlers consuming iron-fortified complementary food, the prevalence of tissue ID was significantly lower both in the ferrous sulfate and ferrous gluconate group compared with the control group after 6 months [37]. Beverages In developed and some developing countries, juice drinks are popular among risk groups for ID, such as women and children. Fruit juice containing encapsulated MFP improved iron status of women with low iron stores in the selected study [41]. The RBV of encapsulated MFP (SunActive Fe, 57 Fe-labeled experimental compound, average median diameter 0.2 µm) in apple juice given to adult women (SF µg/l) was 60%. Ferrous bisglycinate can be used to fortify beverage powders containing multiple micronutrients. In Brazil, ferrous sulfate was evaluated as iron fortificant for orange juice and water. Sensory studies showed that 1 mg iron/l in form of ferrous sulfate produced small color changes in iron-fortified water. Adverse health effects of increased iron intake or increased iron stores The Tolerable Upper Intake Level (UL) for iron established by the US Institute of Medicine, namely 45 mg iron per day for apparently healthy adults ( 19 years), is based on gastrointestinal side effects, such as constipation and diarrhea. These problems are attributed to free iron in the intestine following the ingestion of supplemental iron mostly in the fasting state. The approach used to establish the UL has been criticized because the intake of iron supplements does not resemble dietary iron intake. Iron-fortified foods do not provide free iron and do not cause gastrointestinal side effects [13, 47]. However, adverse health effects of increased dietary iron intake are possible. Associations between increased iron intake/increased iron stores and the risk of the development of cardiovascular diseases, cancer, diabetes mellitus Type II, and neurodegenerative diseases have been proposed. Recent research tends to support a causal relationship between increased iron intake and/or increased iron stores and the development of cardiovascular diseases and colorectal cancer. In people with hereditary hemochromatosis, iron accumulation might lead to liver cirrhosis, diabetes mellitus, cardiomyopathy, arthritis, and hypogonadism. Excessive intake of highly bioavailable iron ( mg iron per day) with beer was the major factor causing liver cirrhosis in Bantu siderosis [48, 49, 50]. Epidemiologic studies provide convincing evidence that red meat or processed meat cause colorectal cancer. Potential mechanisms include Fe 2+ -mediated production of free radicals, in particular hydroxyl radicals (HO ), and heme iron-mediated formation of N-nitroso compounds as well as hyperproliferation [51, 52]. In addition, iron is required for the proliferation of tumor cells. The development of cardiovascular diseases as a consequence of increased iron stores is more likely to be due to the oxidative damage of cardiomyocytes rather than due to atherosclerosis [48]. However, the oxidation of low density lipoproteins via non-transferrin-bound plasma iron (NTBI) has been suggested. Considering the possibility of adverse health effects, the Panel on Dietetic Products, Nutrition, and Allergies of the European Food Safety Authority reports that the UL for iron cannot be established at the present time [50]. The German Institute for Risk Assessment disadvises additional iron intake via dietary supplements or fortified foods unless recommended by a doctor [53]. Nevertheless, the risk of adverse effects from high dietary iron intake, including iron from iron-fortified foods, is considered to be low for the population of European countries (except for homozygotes for hereditary hemochromatosis) [50]. The monitoring of the iron status of populations consuming iron-fortified foods reveals changes in iron stores and helps to adjust fortification programs [1]. Van Thuy et al. [28] reported that the 5 th, 50 th, and 95 th percentile values for SF concentrations were

9 Iron metabolism and prevention of iron deficiency via iron fortification of foods 9 higher in Vietnamese women (16 49 years) consuming iron-fortified fish sauce for 18 months than in US women of childbearing age (31 50 years). Calculated iron stores for women at these percentiles were higher in Vietnamese women. The high prevalence of thalassemias and related hemoglobinopathies in South and Southeast Asia might have increased the effect of iron fortification. In adult males, SF concentration > 200 µg/l indicates severe risk of iron overload [14] and > 300 µg/l, in the presence of transferrin saturation > 52%, indicates iron overload [50]. According to the 3 rd National Health and Nutrition Survey in the USA, mean SF concentration is 204 µg/l in elderly US men (51 70 years) and 120 µg/l in elderly US women (51 70 years). While aging is associated with increased SF levels [13], iron stores do not grow with age [18]. It is not known at which point elevated SF poses a risk of health problems [50], and the increase in SF is not specific for the increase in iron stores [13]. Therefore, a single SF measurement should not be used to describe iron stores in adult males and postmenopausal women if confounding factors cannot be excluded. Conclusions Regular intake of iron-fortified foods is effective in curing nutritional iron deficiency. Such interventions should be targeted at people with low iron status who fail to improve their iron deficiency by means of dietary modification. Targeted iron fortification programs can be considered in Western countries. Possible food vehicles include wheat- or rice-based foods, salt, beverages, and cow s milk-based foods. Further studies investigating iron absorption from ferrous fumarate and ferrous pyrophosphate are needed to clarify whether solely iron status is responsible for the lower upregulation of iron absorption from these fortificants compared with the upregulation of iron absorption from ferrous sulfate observed in iron-deficient subjects. It should be also investigated as to whether this relationship applies to other fortificants that are poorly water-soluble or water-insoluble. Relative bioavailability values (RBVs) of iron fortificants depend both on food matrix and on the iron status of participants. Therefore, background information about these factors is necessary in order to interpret the RBVs correctly. Iron intake exceeding requirements might cause adverse health effects. The relationship between increased iron intake/increased iron stores and health problems requires further investigation. Also, factors responsible for the increase in serum ferritin level associated with aging should be determined. References [1] WHO. FAO. Guidelines on food fortification with micronutrients. Allen LH, de Benoist B, Dary O, Hurrell R (eds). Geneva: World Health Organization and Food and Agriculture Organization of the United Nations; [2] Hurrell RF. Preventing iron deficiency through food fortification. Nutr Rev. 1997; 55: [3] Hurrell R, Egli I. Iron bioavailability and dietary reference values. Am J Clin Nutr. 2010; 91: 1461S-1467S. [4] SCF. Reports of the Scientific Committee for Food (Food Science and techniques series, Thirty-first series). Nutrient and energy intakes for the European Communittee (Opinion expressed on 11 December 1992). Luxembourg: Commission of the European Communitties; [5] Hallberg L, Rossander-Hultén L. Iron requirements in menstruating women. Am J Clin Nutr. 1991; 54: [6] WHO. FAO. Vitamin and mineral requirements in human nutrition (Report of the joint FAO/WHO Expert Consultation, Bangkok, 1998; 2 nd edn.). Geneva: World Health Organization and Food and Agriculture Organization of the United Nations; [7] Mackenzie B, Garrick MD. Iron Imports. II. Iron uptake at the apical membrane in the intestine. Am J Physiol Gastrointest Liver Physiol. 2005; 289: G981-G986. [8] Anderson GJ, Frazer DM, McLaren GD. Iron absorption and metabolism. Curr Opin Gastroenterol. 2009; 25: [9] Dary O, Freire W, Kim S. Iron compounds for food fortification: guidelines for Latin America and the Caribbean Nutr Rev. 2002; 60: S50-S61. [10] Han O. Molecular mechanism of intestinal iron absorption. Metallomics. 2011; 3: [11] Chua AC, Graham RM, Trinder D, Olynyk JK. The regulation of cellular iron metabolism. Crit Rev Clin Lab Sci. 2007; 44: [12] Wienk KJH, Marx JJM, Beynen AC. The concept of iron bioavailability and its assessment. Eur J Nutr. 1999; 38: [13] IoM. Dietary Reference Intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. Washington DC: National Academy Press; [14] UNICEF. UNU, WHO: Iron deficiency anaemia: assessment, prevention, and control. A guide for

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