Helicobacter pylori infection, iron absorption, and gastric acid secretion in Bangladeshi children

¹ From the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B): Centre for Health and Population Research, Dhaka, Bangladesh (SAS, HM, and GJF); the Laboratory for Human Nutrition, Institute of Food Science and Nutrition, Swiss Federal Institute of Technology, Zurich, Switzerland (LD, TW, and RFH); the Department of Internal Medicine, University of Basel, Switzerland (NG); and the Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock (GJF)

² Supported by a grant from the National Institutes of Health (DK 53032-02) and by the Swiss Federal Institute of Technology, Zurich, Switzerland.

³ Address reprint requests to SA Sarker, ICDDR, B, Centre for Health & Population Research, Mohakhali 4, Dhaka 1212, Bangladesh. E-mail: sasarker{at}icddrb.org.

⁴ Address correspondence to GJ Fuchs, University of Arkansas for Medical Sciences, Department of Pediatrics, Mail Stop 512-7, Little Rock, AR 72205. E-mail: gjfuchs{at}usa.net.

ABSTRACT  
Background: Nonheme-iron absorption requires an acidic milieu. Reduced gastric acid output as a consequence of Helicobacter pylori infection could be an important limiting factor for iron absorption.

Objective: We measured gastric acid output and iron absorption from a non-water-soluble iron compound (ferrous fumarate) and a water-soluble iron compound (ferrous sulfate) in children with and without H. pylori infection.

Design: Gastric acid output was quantified before (basal acid output, or BAO) and after pentagastrin stimulation (stimulated acid output, or SAO) in 2–5-y-old children with iron deficiency anemia who were (n = 13) or were not (n = 12) infected with H. pylori. Iron absorption was measured by using a double-stable-isotope technique. H. pylori-infected children were studied before and after eradication therapy.

Results: BAO and SAO were significantly lower in the H. pylori-infected children (0.2 ± 0.2 and 1.6 ± 0.9 mmol/h, respectively) than in the uninfected children (0.9 ± 0.7 and 3.1 ± 0.9 mmol/h, respectively; P = 0.01 and P < 0.005). BAO and SAO improved to 0.8 ± 1.3 and 3.3 ± 2.4 mmol/h, respectively, after therapy. Iron absorption from ferrous sulfate was significantly greater than that from ferrous fumarate both before (geometric Conclusions: Iron absorption from ferrous fumarate was significantly lower than that from ferrous sulfate in both H. pylori-infected and uninfected Bangladeshi children. Treatment of H. pylori infection improved gastric acid output but did not significantly influence iron absorption. The efficacy of ferrous fumarate in iron fortification programs to prevent iron deficiency in young children should be evaluated.

Key Words: Helicobacter pylori • gastric acid secretion • iron absorption • anemia • ferrous fumarate • iron status • children

INTRODUCTION  
Iron deficiency is a major public health problem, especially in infants, children, and women of childbearing age in developing countries (1, 2). The consequences of iron deficiency anemia (IDA) are particularly significant in infants and young children and include abnormalities of immune function, poor growth, and potentially irreversible deficits of cognition and motor function (2).

Low dietary intake of poorly bioavailable iron is believed to be the principal cause of IDA in the developing world. Dietary iron in resource-poor areas is predominantly nonheme iron of plant origin, which contains high amounts of inhibitors of iron absorption, such as phytate (3). Gastric acid secretion is also an important intraluminal factor for nonheme-iron absorption (4, 5). Ingested dietary ferric (Fe³⁺) iron is solubilized and ionized by gastric acid and reduced to the more readily absorbed ferrous (Fe²⁺) form. Conditions affecting gastric acid secretion are therefore potentially important factors in the etiology of IDA (6).

Helicobacter pylori infection is the most common infection worldwide. Its prevalence is very high in developing countries, such as in Bangladesh, where 60% of children aged <5 y are infected (7). Infection is typically acquired in childhood and persists throughout life, causing chronic gastritis, a risk factor for gastric atrophy and gastric cancer (8). Among infected children who have undergone endoscopy, chronic gastritis is a near universal finding (9, 10). An important consequence of chronic H. pylori gastritis and gastric atrophy is low gastric acid output (11). Low gastric acid secretion results in an impaired "gastric barrier," which is associated with increased susceptibility to enteric infections, a major public health concern linked to diarrhea, malnutrition, and growth failure in children in the developing world (12, 13). Several reports have indicated an association between H. pylori infection and anemia, iron deficiency, and IDA, although the nature of the interactions has not been established (14–17).

Iron fortification of foods is considered among the most cost-effective approaches to preventing iron deficiency (18). Non-water-soluble iron compounds are often used in fortification programs because they cause no unacceptable organoleptic changes in the fortified food. However, these compounds are also poorly soluble in gastric secretions, and the bioavailability of iron is low. Ferrous fumarate is a common fortificant of infant cereals that, because it is soluble in dilute acid but poorly soluble in water, causes less organoleptic changes in the food vehicle than do water-soluble compounds (19, 20). However, if gastric acid output is compromised in a large proportion of the target population, the effect of food fortification programs using ferrous fumarate might be less than expected as a result of a reduced capacity to absorb iron from the fortified food.

The aim of the present study was to measure gastric acid secretion and iron absorption from a non-water-soluble iron compound (ferrous fumarate) and from a water-soluble iron compound (ferrous sulfate) before and after treatment in young Bangladeshi children infected with H. pylori. For comparison, uninfected children in the same community were studied in parallel at baseline. All children had IDA.

SUBJECTS AND METHODS  
Subjects
Iron-deficient anemic children with and without H. pylori infection were recruited from Nandipara, a periurban community 7 km from Dhaka City, where the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B), maintains a field clinic and has previously conducted studies (7). The prevalence of H. pylori infection in children <5 y old in this community is 60% (21). A survey of children in the community was conducted to identify all those meeting the study eligibility criteria. Apparently healthy children aged 2–5 y with a weight-for-age >60% of the National Center for Health Statistics median were selected sequentially from the survey list and were screened for H. pylori infection by a [¹³C]urea breath test and for IDA (hemoglobin <110 g/L and serum ferritin <12 µg/L) (22–24). Children with severe anemia (hemoglobin <70 g/L) or apparent infection or inflammatory process—such as fever, cough, or other sign of infection, including ear discharge—were excluded. The children's parents were informed of the study aims and procedures, and written informed consent was obtained from at least one parent. The children (accompanied by their mothers) were admitted for 3 d to the metabolic ward at the ICDDR,B for gastric acid output testing and administration of labeled test meals for measurements of iron absorption. The study protocol was approved by the Ethical and Research Review Committees of the ICDDR,B: Centre for Health and Population Research, Dhaka, Bangladesh.

Iron status
Blood was collected by venipuncture, placed in EDTA-containing and plain tubes, and processed in the laboratory within 3 h of collection for measurement of hemoglobin and ferritin. Hemoglobin was quantified by the cyanmethemoglobin method (Sigma, St Louis) and plasma ferritin by enzyme-linked immunosorbent assay (Ramco, Houston). Commercial quality-control materials (Diamed Diagnostics and Medical Products, Cressier s/Morat, Switzerland and Ramco) were analyzed in parallel. The CVs for the hemoglobin and ferritin quality controls were in the ranges of 1–2% and 2.5–4%, respectively.

[¹³C]Urea breath test
Breath samples were collected in evacuated tubes for the measurement of baseline ¹³C:¹²C isotope ratios after the children had fasted for 2 h. The children first consumed cow milk (25 mL), followed by 100 mg [¹³C]urea (99%) in 25 mL water (Tracer Technologies, Boston) 30 min later. Breath samples were collected 30 min later by using a pediatric mask. Duplicate samples were analyzed for ¹³C:¹²C isotope ratios in respiratory carbon dioxide by isotope ratio mass spectrometry at the Department of Medicine and Research, University of Basel, Switzerland. Breath samples 3.5 over baseline (¹³C:¹²C isotope ratios) were regarded as being positive for H. pylori infection (21). The [¹³C]urea breath test has been shown to be 100% sensitive and 92% specific and is considered a reference standard for the diagnosis of H. pylori infection in children (25).

Gastric acid secretion
After the children had fasted for 5 h, a soft nasogastric tube was introduced. After aspiration of the resting gastric juice, basal samples were collected for 30 min. Pentagastrin (Cambridge Laboratories, Newcastle on Tyne, United Kingdom) was administered subcutaneously (6 µg/kg), and gastric juice aspiration was continued for an additional 60 min. Samples were collected and stored in 15-min aliquots. The acidity of each sample was measured by titration of 1 mL gastric juice with 0.01 N sodium hydroxide to a pH of 7.4 by using an automated titrator (Metrohm, Herisau, Switzerland). Acid output was calculated for each time point by multiplying the volume of gastric juice by the respective acid concentration. Basal acid output and stimulated acid output were calculated based on 2 samples collected for baseline measurement and the 4 samples collected after the administration of pentagastrin and were expressed as mmol/h.

Test meal and isotopic labels
Iron absorption from ferrous fumarate was compared with that from a highly bioavailable, water-soluble iron compound (ferrous sulfate) in a randomized crossover study by use of a double stable-isotope technique. Incorporation of ⁵⁷Fe and ⁵⁸Fe into erythrocytes 14 d after administration was used as an index of iron absorption (26). An infant cereal (Ceresoy; Nestlé, Vevey, Switzerland) based on wheat and soy and without any added iron or ascorbic acid was produced especially for the study. Test meals consisted of 25 g dry cereal mixed with 100 g hot deionized water. Ascorbic acid (molar ratio of 3:1; ascorbic acid relative to added iron) and [⁵⁷Fe]ferrous fumarate or ⁵⁸FeSO₄ (10 mg Fe/100 g dry cereal) were added to the test meals before serving. The children were randomly assigned to start with the test meal labeled with ⁵⁷Fe or that labeled with ⁵⁸Fe. Cereal iron and calcium contents were quantified by electrothermal flame atomic absorption spectroscopy after mineralization by microwave digestion with an HNO₃/H₂O₂ mixture and by standard addition technique to minimize matrix effects. Phytic acid content was measured by using an HPLC technique (27).

[⁵⁷Fe]Ferrous fumarate from the same batch used in previous iron absorption studies was used (28, 29). ⁵⁸FeSO₄ was prepared from highly enriched ⁵⁸Fe dissolved in 0.1 mol H₂SO₄/L.

Analysis of isotopic composition of blood samples
Whole blood was mineralized by microwave digestion, and iron was separated by anion-exchange chromatography following a solvent-solvent extraction step into diethylether. Iron was analyzed by negative thermal ionization mass spectrometry by using FeF₄^– molecular ions with a magnetic sector field mass spectrometer (MAT 262; Finnigan MAT, Bremen, Germany) equipped with a multicollector system for simultaneous ion beam detection. We used the negative thermal ionization technique for iron of Walczyk et al (30, 31).

On the basis of the shift of iron isotope ratios in the blood samples and the amount of iron circulating in the body, the amounts of the ⁵⁷Fe and ⁵⁸Fe labels present in the blood of the children 14 d after administration were calculated according to isotope-dilution principles. Circulating iron was calculated based on blood volume and hemoglobin concentration (32). For calculation of fractional absorption, 90% incorporation of the absorbed iron into red blood cells was assumed (33).

Study design
Body weight and height were measured and a venous blood sample was drawn into EDTA-coated tubes after the children had fasted for 6–8 h. The blood drawing was followed by intake of the first labeled test meal. The second test meal was fed on the following day under identical conditions. No food or fluid was given for 3 h after the labeled test meals. On day 16, a venous blood sample was drawn at the clinic in Nandipara, and body weight and height were re-measured.

After a second blood sample was collected, H. pylori-infected children began a 14-d course of anti-H. pylori therapy of amoxicillin (30 mg · kg^–1 · d^–1), clarithromycin (15 mg · kg^–1 · d^–1), and omeprazole (20 mg/d) given in 2 divided doses daily by health workers at home. Four weeks after completing the treatment (day 60), the H. pylori-infected children were readmitted to the metabolic study ward for the repeat iron absorption, gastric acid output, and [¹³C]urea breath tests. All children were provided therapeutic ferrous sulfate (3 mg · kg^–1 · d^–1) on completion of the study.

Data analyses
Paired and unpaired t tests were used to evaluate results within and between the 2 groups. Wilcoxon's signed-ranks test was used to compare paired observations, such as acid outputs before and after treatment, when values were not normally distributed. Iron absorption and plasma ferritin were logarithmically transformed before analysis, and the results are presented as geometric means (+1 SD, –1 SD). All other results are presented as means ± SDs. SPSS (version 8 for WINDOWS; SPSS Inc, Chicago) was used to perform the statistical analyses.

RESULTS  
Twenty-five children (13 with H. pylori infection and 12 uninfected) with IDA entered the study. In the infected group, incomplete intake of the labeled test meals resulted in the exclusion of one child at baseline and one child after treatment. One H. pylori-infected child was lost to follow-up after treatment because of migration from the community. The baseline characteristics of the children in the 2 groups were not significantly different (Table 1). Of the 12 H. pylori-infected children, 10 had a negative result on the urea breath test after treatment. The infant cereal contained 2.0 ± 0.02 mg Fe, 45.0 ± 0.3 mg Ca, and 0.41 g phytic acid per 100 g cereal product.

View this table:
TABLE 1. Baseline characteristics of the study children¹

 
Gastric acid output was significantly lower in H. pylori-infected children than in uninfected children (Table 2). Both basal and stimulated acid output improved after H. pylori eradication therapy and reached amounts not significantly different from those of uninfected children.

View this table:
TABLE 2. Gastric acid output before and after stimulation with pentagastrin in Helicobacter pylori-infected and uninfected children with iron deficiency anemia¹

 
Geometric mean iron absorption from ferrous sulfate and ferrous fumarate was 19.7% and 5.3% (P < 0.0001; n = 12) before treatment and 22.5% and 6.4% after treatment (P < 0.0001; n = 11) in H. pylori-infected children (Table 3). Corresponding values for uninfected children were 15.6% and 5.4% (P < 0.001; n = 12). Geometric mean relative absorption (absorption of ferrous fumarate compared with that of ferrous sulfate) was 26.9% and 34.8% in H. pylori-infected and uninfected children, respectively, and 28.3% in H. pylori-infected children after treatment. H. pylori eradication therapy did not significantly influence iron absorption from ferrous sulfate or ferrous fumarate (P = 0.34; n = 10).

View this table:
TABLE 3. Fractional iron absorption from ferrous fumarate and ferrous sulfate in uninfected children with iron deficiency anemia (IDA) and in Helicobacter pylori-infected children with IDA before and after treatment

 
Hemoglobin improved significantly in the H. pylori-infected children with treatment; mean hemoglobin increased from 99 ± 7 to 109 ± 5 g/L after treatment (P < 0.005), whereas there was no significant difference in hemoglobin over the same period in the uninfected children (104 ± 7 and 108 ± 7 g/L; P > 0.05).

DISCUSSION  
A prominent finding in the present study was that H. pylori infection was associated with impaired gastric acid secretion, although the reduced gastric acid secretion did not significantly influence iron absorption from the 2 iron compounds evaluated in this study. No statistically significant improvement in iron absorption of either ferrous sulfate or ferrous fumarate was observed after H. pylori eradication therapy despite improvement in gastric acid secretion. Our results do not support the hypothesis that H. pylori infection influences iron absorption from water-soluble or non-water-soluble iron compounds. Our study population was relatively young (2–5 y), however, and it is conceivable that the effect of H. pylori infection on gastric acid secretion and iron absorption is more pronounced after long-term exposure to the infection.

Although H. pylori infection has been associated with iron deficiency and IDA, the mechanism of causality is poorly defined (14–16). Our results indicate that H. pylori infection per se does not influence iron absorption in young children. The statistically significant increase in hemoglobin concentration after eradication therapy suggests an important role of H. pylori infection in the etiology of anemia. Although we could not demonstrate an influence on iron absorption in the present study, the increase in gastric acid output may have resulted in an improved absorption of native food iron. It is possible that H. pylori competes with the host for iron absorption because the organism contains an iron binding protein similar to ferritin and a system of iron-repressive outer membrane proteins with binding activity for heme iron (34, 35). Yet this is unlikely to explain the observations in our children because heme iron intake is negligible in this study population.

A beneficial role of antibiotics in eradicating a coexistent, subclinical infection or in reducing the inflammatory response in association with H. pylori infection is another possibility, because anemia can be caused by infection or by general inflammatory disorders through an effect on iron metabolism (36). The systemic inflammatory response to H. pylori infection is probably mild but has not been evaluated as a potential cause of H. pylori-associated anemia. Gastrointestinal blood loss was reported in association with H. pylori infection in one study, but other studies have not confirmed this, and we have not observed gastrointestinal blood loss in H. pylori-infected children in Bangladesh (15; S Sarker and GJ Fuchs, unpublished observations, 2003). Although the mechanism of H. pylori infection in the etiology of anemia and IDA remains to be fully defined, it is likely that this infection should be considered together with gastrointestinal parasites (such as hookworm), malaria, and other infections when developing public health strategies to combat anemia and IDA.

The second major finding of the current study was that iron absorption from ferrous fumarate was significantly lower than that from ferrous sulfate. Its mean absorption relative to ferrous sulfate in both H. pylori-infected and uninfected children was only 27–35% compared with 100% in Western adults (19, 20). Although gastric acid secretion improved after anti-H. pylori treatment, iron absorption was not influenced. These results indicate that gastric acid output after treatment was still too low to optimally solubilize ferrous fumarate. Gastric acid secretion in our uninfected children and H. pylori-infected children posttreatment was similar to that in apparently healthy children in Bangladesh and the United States (37, 38). It can therefore be expected that the low relative iron absorption from ferrous fumarate observed in the present study is not specific to children living in developing countries but can also be expected in healthy Western children. It should be emphasized that the Bangladeshi children had IDA and were less well nourished than are Western children and that the influence of these conditions on the results is not known.

Only limited information is available on iron absorption from non-water-soluble iron compounds in young children, and no data on iron absorption from ferrous fumarate have been reported in 2–5-y-old children living in industrialized countries. The labeled ferrous fumarate compound used in the present study has been previously evaluated and found to be significantly better absorbed than ferric pyrophosphate in European infants (28). Although the labeled compound was not previously compared directly against ferrous sulfate in children, recent data from Guatemala indicate that iron absorption from ferrous fumarate and ferrous sulfate is similar in 12-y-old children (29).

We conclude that gastric acid output was impaired in H. pylori-infected children compared with that in uninfected children and that treatment of H. pylori infection improved gastric acid output and hemoglobin concentrations but did not significantly influence iron absorption. Furthermore, contrary to observations in healthy Western adults, iron absorption from ferrous fumarate was significantly lower than that from ferrous sulfate in both H. pylori-infected and uninfected Bangladeshi children. The effect of iron fortification programs that use ferrous fumarate or other non-water-soluble iron compounds to prevent iron deficiency in children such as ours should be defined.

ACKNOWLEDGMENTS  
We gratefully acknowledge the participation in the present study of the children and their parents. We thank Pius Hildebrand, University of Basel, for analysis of breath samples (urea breath test); Christophe Zeder, Swiss Federal Institute of Technology, Zurich, for analysis of iron stable isotopes in blood samples and food analyses; MA Wahed for performing the biochemical iron status assays; Rekha Chanda (ICDDR,B) for excellent coordination of the fieldwork; and the nurses in the metabolic ward at the ICDDR,B for their care.

SAS was responsible for the design of the study, data collection and analysis, and writing of the manuscript; LD was responsible for the design of the study, data collection and analysis, and writing of the manuscript; HM was responsible for data collection; TW was responsible for data collection and analysis and manuscript review; RFH was responsible for the design of the study and manuscript review; NG was responsible for data collection and analysis and manuscript review; and GJF was responsible for the design of the study, data analysis, and writing of the manuscript. None of the authors had a conflict of interest with any of the organizations sponsoring the research, including advisory board affiliations.

REFERENCES  

1. United Nations Children Fund, United Nations University, and World Health Organization. Iron deficiency anaemia: assessment, prevention and control, a guide for programme managers. Geneva: World Health Organization, 2001.
2. UNICEF/UNU/WHO consultation. Iron deficiency anaemia: assessment, prevention, and control. Geneva, Switzerland: WHO, 2001. (WHO/NHD/01.3.)
3. Hallberg L, Rossander L, Skanberg AB. Phytate and inhibitory effect of bran on iron absorption in man. Am J Clin Nutr 1987;45:988–96.
4. Skikne BS, Lynch SR, Cook JK. Role of gastric acid in food iron absorption. Gastroenterology 1981;81:1068–71.
5. Fairbanks VF, Fahey JL, Beutler E. The metabolism of iron. In: clinical disorders of iron metabolism. 2nd ed. New York: Grune & Stratton, 1971:42–127.
6. McColl KEL, El-Omar E, Gillen D. Interactions between H. pylori infection, gastric acid secretion and anti-secretory therapy. Br Med Bull 1998;54:121–38.
7. Sarker SA, Mahalanabis D, Hildebrand P, et al. Helicobacter pylori: prevalence, transmission, and serum pepsinogen II concentrations in children of a poor peri-urban community in Bangladesh. Clin Infect Dis 1997;25:990–5.
8. Kuipers EJ, Uyterlinde AM, Pena AS, et al. Long-term sequelae of Helicobacter pylori gastritis. Lancet 1995;345:1525–8.
9. Gold BD, van Doorn L, Guarner J, et al. Genotype, clinical, and demographic characteristics of children infected with Helicobacter pylori. J Clin Microbiol 2001;39:1348–52.
10. Bahu Mda G, da Silveira TR, Maguilnick I, Ulbrich-Kulczynski J. Endoscopic nodular gastritis: an endoscopic indicator of high-grade bacterial colonization and severe gastritis in children with Helicobacter pylori. J Pediatr Gastroenterol Nutr 2003;36:217–22.
11. El-Omar EM, Oien K, El-Nujumi A, et al. Helicobacter pylori infection and chronic gastric acid hyposecretion. Gastroenterology 1997;113:15–24.
12. Dale A, Thomas JF, Darboe MK, Coward WA, Harding M, Weaver LT. Helicobacter pylori infection, gastric acid secretion, and infant growth. J Pediatr Gastroenterol Nutr 1998;26:393–7.
13. Passaro DJ, Taylor DN, Meza R, Cabera L, Gilman RH, Parsonet J. Acute Helicobacter pylori infection is followed by an increase in diarrhoeal disease among Peruvian children. Pediatrics [serial online] 2001;108:e87.Internet: http://pediatrics.aappublications.org/content/vol108/issue5/index.shtml (accessed 9 April 2004).
14. Seo JK, Ko JS, Choi KD. Serum ferritin and Helicobacter pylori infection in children: a seroepidemiologic study in Korea. J Gastroenterol Hepatol 2002;17:754–7.
15. Kostaki M, Fessatou S, Karpathios T. Refractory iron deficiency anemia due to silent Helicobacter pylori gastritis in children. Eur J Paediatr 2003;162:177–9.
16. Marignani M, Angeletti S, Bordi C, et al. Reversal of long standing iron deficiency anaemia after eradication of Helicobacter pylori infection. Scand J Gastroenterol 1997;32:617–22.
17. Yip R, Limburg PJ, Ahlquist DA, et al. Pervasive occult gastrointestinal bleeding in an Alaska native population with prevalent iron deficiency. JAMA 1997;277:1135–9.
18. Hurrell RF. Iron. In: Hurrell RF, ed. The mineral fortification of foods. Surrey, United Kingdom: Leatherhead Fodd RA, K Leatherhead Publishing, 1999:54–93.
19. Hurrell RF, Furniss DE, Burri J, Whittaker P, Lynch SR, Cook JD. Iron fortification of infant cereals: a proposal for the use of ferrous fumarate or ferrous succinate. Am J Clin Nutr 1989;49:1274–82.
20. Hurrell RF, Reddy MB, Dassenko SA, Cook JD, Shepherd D. Ferrous fumarate fortification of a chocolate drink powder. Br J Nutr 1991;65:271–83.
21. Sarker SA, Rahman MM, Mahalanabis D, et al. Prevalence of Helicobacter pylori infection in infants and family contacts in a poor Bangladesh community. Dig Dis Sci 1995;40:2669–72.
22. Hamil PV, Drizd TA, Johnson CL, et al. Physical growth: National Center for Health Statistic Percentages. Am J Clin Nutr 1979;32:607–29.
23. Logan RP, Polson RJ, Misiewiez JJ, Rao G, Karim NQ, Newell D, et al. Simplified single sample ¹³carbon urea breath test for Helicobacter pylori: comparison with histology, culture, and ELISA serology. Gut 1991;32:1461–4.
24. WHO/UNICEF/UNU Consultation. Indicators and strategies for iron deficiency and anaemia programmes. Geneva: World Health Organization, 1993.
25. Rowland M, Lambert I, Gormally S, et al. Carbon 13-labeled urea breath test for the diagnosis of Helicobacter pylori infection in children. J Pediatr 1997;131:815–20.
26. Kastenmayer P, Davidsson L, Galan P, Cherouvrier F, Hercberg S, Hurrell RF. A double stable isotope technique for measuring iron absorption in infants. Br J Nutr 1994;71:411–24.
27. Sandberg A-S, Ahderinne R. HPLC method for determination of inositol tri-, tetra-, penta-, and hexaphosphates in foods and intestinal contents. J Food Sci 1986;51:547–50.
28. Davidsson L, Kastenmayer P, Szajewska H, Hurrell RF, Barclay D. Iron bioavailability in infants from an infant cereal fortified with ferric pyrophosphate or ferrous fumarate. Am J Clin Nutr 2000;71:1597–602.
29. Davidsson L, Dimitriou T, Boy E, Walczyk T, Hurrell RF. Iron bioavailability from iron-fortified Guatemalan meals based on corn tortillas and black bean paste. Am J Clin Nutr 2001;75:535–9.
30. Walczyk T. Iron isotope ratio measurements by negative thermal ionization mass spectrometry. Int J Mass Spectrum Ion Proc 1996;161:217–27.
31. Walczyk T, Davidsson l, Zavaleta N, Hurrell RF. Stable isotope labels as a tool to determine iron absorption by Peruvian school children from a breakfast meal. Fresenius J Anal Chem 1997;359:445–9.
32. Linderkamp O, Versmold HT, Riegel KP, Betke K. Estimation and prediction of blood volume in infants and children. Eur J Pediatr 1977;125:227–34.
33. Rios E, Hunter RE, Cook JD, Smith NJ, Finch CA. The absorption of iron as supplements in infant cereal and infant formulas. Pediatrics 1975;55:686–9.
34. Annibale B, Capurso G, Martino G, Grossi C, Delle Fave G. Iron deficiency anaemia and Helicobacter pylori infection. Int J Antimicrob Agents 2000;16:515–9.
35. Jurado RL. Iron, infections, and anemia of inflammation. Clin Infect Dis 1997;25:888–95.
36. Yip R, Dallman PR. The role of inflammation and iron deficiency as causes of anemia. Am J Clin Nutr 1988;48:1295–300.
37. Gilman RH, Paranen R, Brown KH, et al. Decreased gastric acid secretion and bacterial colonization of the stomach in severely malnourished Bangladeshi children. Gastroenterology 1988;94:1308–14.
38. Euler AR, Byrne WJ, Campbell MF. Basal and pentagstrin-stimulated gastric acid secretory rates in normal children and those with peptic ulcer disease. J Pediatr 1983;103:766–78.