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Community and International Nutrition

Estimation of the Effect of the Acute Phase Response on Indicators of Micronutrient Status in Indonesian Infants¹

Frank T. Wieringa^*,, Marjoleine A. Dijkhuizen^*,, Clive E. West^*,**2, Christine A. Northrop-Clewes and Muhilal

^* Division of Human Nutrition and Epidemiology, Wageningen University, The Netherlands; Nutrition Research and Development Centre, Bogor, Indonesia; ^** Department of Gastroenterology, University Medical Centre Nijmegen, The Netherlands; and Northern Ireland Centre of Diet and Health, University of Ulster, Coleraine, BT52 1SA, Northern Ireland, UK

²To whom correspondence should be addressed. E-mail: clive.west{at}staff.nutepi.wau.nl.

	ABSTRACT

TOP ABSTRACT INTRODUCTION SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Many indicators of micronutrient status change during infection because of the acute phase response. In this study, relationships between the acute phase response, assessed by measuring concentrations of C-reactive protein (CRP), ₁-antichymotrypsin (ACT) and ₁-acid glycoprotein (AGP), and indicators of micronutrient status were analyzed in 418 infants who completed a 6-mo randomized, double-blind, placebo-controlled, supplementation trial with iron, zinc and/or ß-carotene. The acute phase response, defined by raised CRP (plasma concentration >10 mg/L), raised AGP (>1.2 g/L), or both raised CRP and AGP, significantly affected indicators of iron, vitamin A and zinc status, independently of the effects of supplementation. Plasma ferritin concentrations were higher by 15.7 (raised AGP) to 21.2 (raised CRP and AGP) µg/L in infants with elevated acute phase proteins compared with infants without acute phase response (P < 0.001). In contrast, plasma concentrations of retinol were lower by 0.07 (P < 0.05, raised AGP) to 0.12 (P < 0.01, raised CRP) µmol/L, and of zinc lower by 1.49 (P < 0.01, raised AGP) to 1.89 (P < 0.05, raised CRP and AGP) µmol/L. Hemoglobin concentrations and the modified relative dose response were not affected. Consequently, the prevalence of iron deficiency anemia was underestimated in infants with raised acute phase proteins by >15%, whereas the prevalence of vitamin A deficiency was overestimated by >16% compared with infants without acute phase response. Hence, using indicators of micronutrient status without considering the effects of the acute phase response results in a distorted estimate of micronutrient deficiencies, whose extent depends on the prevalence of infection in the population.

KEY WORDS: • vitamin A • zinc • ferritin • hemoglobin • modified relative dose response • acute phase proteins

	INTRODUCTION

TOP ABSTRACT INTRODUCTION SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Micronutrient status defines the amount of a micronutrient available for metabolic functions, with body stores as the most important determinant of the availability of most micronutrients. Plasma concentrations of micronutrients are often measured as a surrogate for total body stores and micronutrient status, assuming that the distribution between the different compartments is constant. However, during the acute phase response, plasma concentrations of many micronutrients change (1 ). It is unclear whether these changes reflect solely a redistribution or also a change in body stores. During infection, micronutrient losses and requirements are usually increased, eventually also reducing body stores, but most likely not to the extent or as early in infection as the changes in plasma concentrations suggest. Many commonly used indicators of micronutrient status are affected by the acute phase response and may not adequately reflect micronutrient status during infection.

The acute phase response is a generalized reaction of the body to inflammation (2 ). Proteins whose concentrations change as part of the acute phase response are referred to as acute phase proteins. The reaction time and magnitude of change after the onset of inflammation, and also the sensitivity to stimuli can differ. C-reactive protein (CRP)³ is very sensitive, especially to bacterial infections (3 ). Plasma concentrations increase within 10 h of the onset of acute inflammation, and normalize rapidly, usually within 1 wk. However, slight elevations of CRP concentrations can also occur during low grade chronic inflammation such as in coronary artery disease (4 ). ₁-Antichymotrypsin (ACT) concentrations also increase early, but remain elevated for a longer time than CRP. ₁-Acid glycoprotein (AGP) concentrations begin to increase only > 24 h after the onset of inflammation, but remain elevated well into convalescence; thus AGP can be detected weeks after the infection, and concentrations are also elevated in low grade chronic inflammation (2 ,3 ).

The extent to which indicators of micronutrient status are affected by the acute phase response depends not only on the specific indicator used, but also on the severity of infection, the time phase of the acute phase response (3 ), and the nutritional status of the individual (5 ). Many efforts have been made to identify micronutrient status indicators that are not affected by the acute phase response, but with limited success. Another approach, however, is to measure the acute phase response and to quantify the effects on different micronutrient status indicators, so as to enable changes to be taken into account. Several studies have examined vitamin A status in both clinically ill subjects and in apparently healthy subjects in relation to the acute phase response. Plasma retinol concentrations decreased during illness and increased again during recovery. In healthy children, plasma retinol was related to the concentrations of acute phase proteins (6 –9 ). However, the overall effects of the acute phase response on indicators of vitamin A status or other micronutrients are not established sufficiently to enable changes to be predicted, especially at the population level (10 ).

In this study, the sensitivity of several frequently used indicators of micronutrient status to the acute phase response was investigated. The acute phase response was quantified by measuring the concentrations of three different acute phase proteins (CRP, ACT and AGP). For each indicator of micronutrient status studied, the effect of the acute phase response was estimated, as well as the consequences of the estimation on the prevalence of deficiency.

	SUBJECTS AND METHODS

TOP ABSTRACT INTRODUCTION SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Study design and location.

Infants were recruited at 4 mo of age to participate in a randomized, double-blind, placebo-controlled supplementation trial with iron (10 mg/d), zinc (10 mg/d), ß-carotene (2.4 mg/d), iron and zinc combined (10 mg/d each), zinc and ß-carotene combined (10 and 2.4 mg/d, respectively) or placebo. Eligible infants were identified by village health volunteers, and the mothers invited to participate in the study. Mothers or wardens of the infants were informed of the procedures and purpose of the study, and provided written informed consent. The study was carried out in a rural area of Bogor District, West Java, Indonesia between October 1997 and March 1999. After 6 mo of supplementation, a blood sample was taken from the infants to assess micronutrient status and acute phase protein concentrations. A blood sample was collected only from infants who were deemed healthy after clinical examination. All infants with a hemoglobin concentration <110 g/L were given iron supplementation upon completion of the trial. In this report, only the relationships between acute phase proteins and indicators of micronutrient status are presented. The effects of supplementation have been published elsewhere (11 ,12 )

Five h before the blood sampling, the infants received a small dose of 3,4-didehydroretinol in oil (1.5 mg in 700 µL) to measure the modified relative dose response (MRDR). In the MRDR, a ratio of the plasma concentration of 3,4-didehydroretinol to that of retinol > 0.06 is considered indicative of insufficient liver retinol stores (13 ). When liver retinol stores are low, more 3,4-didehydroretinol appears in the blood relative to retinol concentrations. A 5-mL venous blood sample was taken from the nonfasting infants. A closed-tube heparinized vacuum system was used to avoid contamination with zinc (Becton and Dickinson, Leiden, The Netherlands). Blood samples were immediately stored at 4°C to prevent microhemolysis and separated within 5 h. Plasma samples were divided into aliquots and stored at -30°C until analysis. Hemoglobin concentrations were measured by the standard cyanoblue method (Humalyzer, Wiesbaden, Germany). Plasma zinc concentrations were analyzed with flame atomic absorption spectrophotometry (Varian, Clayton, Victoria, Australia) using trace element–free procedures, as described earlier (14 ). The CV (10% duplo analysis and pooled control samples) for zinc analyses was <5%. Plasma concentrations of retinol and 3,4-didehydroxyretinol were measured in the same injected sample by HPLC (Millipore Waters, Harrow, Middlesex, UK) (15 ). The CV (10% duplo analysis and pooled control samples) for the retinol analysis was <10%. Ferritin was measured using a commercial ELISA-kit (IBL-Hamburg, Germany) according to the guidelines of the manufacturer. CRP, ACT and AGP concentrations were measured using immunoturbidimetric techniques (Cobas Fara analyzer, Roche Products, Welwyn, UK). The CV for the ferritin, CRP, ACT and AGP assays were <10%.

Ethical approval.

The protocol was approved by the ethical committee of the National Health Research and Development Institute of Indonesia and by the ethical committee of the Royal Netherlands Academy of Arts and Sciences.

Statistical analysis.

Data were examined for normal distribution using the Kolmogorov-Smirnov test of normality. Plasma concentrations of ferritin were transformed to logarithms before statistical analysis. After logarithmic transformation, correlations between the plasma concentrations of the acute phase proteins were assessed using Pearson’s correlation. Differences in plasma concentrations of the acute phase proteins among the supplementation groups were tested with the nonparametric Kruskal-Wallis test. Differences in prevalence were tested with Pearson’s ² test. Differences in indicators of micronutrient status between groups of infants with no elevations in CRP and AGP and those with raised CRP only, raised AGP only, or both raised CRP and AGP, were analyzed using a general linear model. The supplemented micronutrients were included as covariates to control for the effect of supplementation on micronutrient status indicators. Sex was included in the analysis of ferritin because of significant confounding and in the analysis of plasma zinc because possible confounding gender differences have been reported (16 ). Estimates of the differences (effect sizes) in the indicators of micronutrient status between the different subgroups with raised acute phase proteins and those with no raised acute phase proteins were calculated using the same general linear model. Statistical analysis was carried out with the SPSS 7.5.2 (SPSS, Chicago, IL) software package. Values in the text are means ± SD.

	RESULTS

TOP ABSTRACT INTRODUCTION SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Acute phase proteins and plasma iron and zinc were measured in all 418 infants (Table 1 ). Plasma retinol concentrations were measured in 256 of these infants, with a complete MRDR test available for 238 infants. Before the collection of the blood sample, 90 infants had been supplemented with iron, 94 with zinc, 38 with ß-carotene, 74 with iron and zinc combined, 39 with zinc and ß-carotene combined and 83 with a placebo. The infants were 10.1 ± 0.6 mo old at the time of blood sampling. Concentrations of the acute phase proteins (Table 1) , indicative of an acute phase response, were defined as plasma concentrations of CRP > 10 mg/L, ACT > 0.6 g/L and AGP > 1.2 g/L (6 ). The median plasma concentrations of CRP, ACT and AGP were all within the normal range; however, 15 and 21% of the infants had elevated CRP and AGP concentrations, respectively, and a small proportion had elevated ACT concentrations (4.3%) (Table 1) . The different supplementation groups did not differ in the concentrations of any of the acute phase proteins or in the prevalence of elevated acute phase proteins at the time of blood sampling (Table 1) .

The effects of the acute phase response on indicators of micronutrient status alter the perceived prevalences of micronutrient deficiencies when these indicators are used to define deficiency (Table 3 ). Micronutrient deficiencies were defined according to standard practice as hemoglobin concentration <110 g/L for anemia, anemia combined with a plasma ferritin concentration <12.0 µg/L for iron deficiency anemia, plasma retinol concentration <0.70 µmol/L for vitamin A deficiency, MRDR the ratio <0.06 for insufficient liver stores of vitamin A and zinc deficiency as a plasma zinc concentration <10.7 µmol/L (13 ,17 ). The perceived prevalence of iron deficiency anemia in all infants was 4.5% lower than in the infants with no raised acute phase proteins. In the groups with raised plasma concentrations of acute phase proteins, the perceived prevalence of iron deficiency was lower than in the group in which acute phase protein levels were not raised (P < 0.001 for infants with a raised CRP, P < 0.01 for infants with a raised AGP or both CRP and AGP raised). In contrast, the prevalence of vitamin A deficiency was perceived to be 4.6% higher in all infants than in infants without raised acute phase proteins. The perceived prevalence of vitamin A deficiency was higher in infants with raised levels of CRP (P < 0.001), AGP (P < 0.05) and both CRP and AGP (P < 0.01) compared with infants without raised acute phase protein levels. The perceived prevalence of zinc deficiency followed a pattern similar to that of vitamin A deficiency, with a higher perceived prevalence of deficiency in the infants with raised CRP levels (P < 0.001) and in infants with both raised CRP and AGP levels (P < 0.01) compared with infants without raised acute phase protein levels. The perceived prevalences of anemia and of vitamin A deficiency as indicated by the MRDR were only slightly affected by the acute phase response (P = 0.08, only for infants with raised AGP levels).

	DISCUSSION

TOP ABSTRACT INTRODUCTION SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

Micronutrient deficiencies increase the risk of infection. However, in this study, the perceived higher prevalences of micronutrient deficiencies during infection can be attributed mainly to the effects of the acute phase response, and is unlikely to result from an increased prevalence of infection derived from underlying micronutrient deficiencies. The infants were supplemented with different micronutrients or placebo for 6 mo before blood collection, and neither the concentrations of CRP, ACT or AGP, nor the prevalence of increased concentrations of CRP, ACT or AGP were different among the supplementation groups or the placebo group (Table 1) . Furthermore, in this study, none of the infants had clinical signs of infection at the time of blood collection, also reducing the risk of a confounding effect of possible increased morbidity in deficient infants. Moreover, if preexisting micronutrient deficiencies leading to increased prevalence of an acute phase response were indeed the cause of the increased prevalence of deficiency in the groups with raised acute phase proteins, one would expect iron status as measured by hemoglobin concentrations also to be lower in these groups, especially in view of the concomitant occurrence of various micronutrient deficiencies in this population (14 ). However, hemoglobin concentrations were not different among the groups (Table 3) , giving no indication for increased prevalence of deficiency in the infants with an acute phase response. It must be noted that changes in plasma ferritin concentrations during the acute phase response are different from the changes of plasma retinol and zinc concentrations because ferritin itself can be considered an acute phase protein. In view of this double role, plasma ferritin concentrations do not reliably reflect iron status in the presence of infection. Alternative indicators of iron status that are less sensitive to the acute phase response, such as transferrin receptor concentrations, have therefore been identified, although these often have other limitations (20 ). Furthermore, vitamin A status was measured with two indicators, plasma retinol concentrations and the MRDR. Plasma retinol concentrations were much lower in the infants with raised acute phase proteins, whereas the MRDR was scarcely affected, indicating that vitamin A status itself was not as different in the infants with raised acute phase protein concentrations as the changes in plasma retinol concentrations suggest. The insensitivity of the MRDR to the acute phase response implies that concentrations of 3,4-didehydroretinol decrease in proportion to retinol concentrations during the acute phase response because the MRDR is the ratio of 3,4-didehydroretinol over retinol.

Plasma concentrations of the various acute phase proteins increase at different stages of the acute phase response and respond in different ways to different types of infection (2 ). In general, CRP levels increase early in an infection and return to normal within 1–2 wk, whereas AGP levels increase later in infection but can remain elevated for several weeks. Hence, raised CRP and AGP levels identify different but overlapping groups of subjects. In this study, 61% of the infants with raised CRP levels also had raised AGP levels, and 43% of the infants with raised AGP levels also had raised CRP levels. Although the effect size of CRP on indicators of micronutrient status was apparently larger than that of AGP, an increased plasma concentration of AGP identified more subjects with an acute phase response. In this respect, the validation of the cut-off values used for the acute phase proteins is important. The cut-off values used in this study were those most commonly used to facilitate comparison with other studies. Although these values are based on studies mainly in adults, the prevalences of the acute phase response detected by raised CRP or raised AGP are not very dissimilar, and the prevalences found in this study are comparable with those reported earlier (6 ). However, in this study, the cut-off value used for ACT identified only 4.3% of the infants as having an acute phase response and thus may lack sensitivity. This could be due to the fact that cut-off values for assessing the acute phase response using concentrations of acute phase proteins are based on studies in adults, not infants. During infancy, many metabolic functions are different, including those of the liver, and hence cut-off values specific for infants may be more appropriate. A cut-off value of 0.5 g/L instead of 0.6 g/L for ACT increased the proportion of infants identified as having an acute phase response from 4.3 to 12%, which is more in line with the prevalence identified by raised CRP levels. However, using cut-off values that are too low will reduce the specificity of the acute phase protein concentrations as indicators of an acute phase response.

The effect of the acute phase response on the plasma concentrations of indicators of micronutrient status can be mediated in several ways. During infection, there can be a redistribution of the indicator of micronutrient status, without a real change in the total body content of the micronutrient, resulting in a distorted measurement of the micronutrient status (21 ). Alternatively, requirements and/or losses of a micronutrient can be increased during infection, sometimes in combination with impaired absorption, resulting in a real change in body stores (22 ). This latter effect is probably more important in the long term. When low plasma concentrations result from a redistribution of a nutrient between different body compartments, such lower plasma concentrations may not necessarily reflect lower concentrations in other body compartments (23 ). In fact, there is evidence for increased concentrations of zinc and iron in the liver and the reticuloendothelial system. Also, plasma concentrations reduced during the acute phase response will rebound at least partially when the infection has resolved (3 ). As yet, it is unclear whether the lowering of plasma concentrations of micronutrients carries a physiologic benefit, except for iron for which redistribution has some clear advantages (24 ,25 ) However, there is evidence that the lower plasma retinol concentrations during infection can imperil retinol supply to the eye and induce acute clinical ocular signs of deficiency (26 ).

Populations at risk for micronutrient deficiency are currently identified using indicators sensitive to the acute phase response. For example, the World Health Organization defines vitamin A deficiency a public health problem when the prevalence of serum retinol values <0.70 µmol/L are 2–10% (mild), 10–20% (moderate) or >20% (severe) (27 ). Present cut-off values such as these are based on populations with an unknown prevalence of infection. In this study, for example, only 15% of the infants had a raised CRP, resulting in a 4.6% higher estimation of vitamin A deficiency prevalence in the population compared with the infants with no raised acute phase proteins. Therefore, cut-off values should be based on data from populations without infections, or include a correction factor for the prevalence of infection to account for the effect of the acute phase response. This is especially important when comparing populations because the overall effect of the acute phase response on the measurement of micronutrient status is dependent on the prevalence of infection in the population. Patterns and prevalences of infections can vary widely among populations and subgroups within populations. Furthermore, several studies have shown that clinical examination does not rule out the presence of an acute phase response (6 ,14 ). Hence, the micronutrient status of populations can not be confidently compared without considering biomarkers of the acute phase response.

Including a measure of the acute phase response in the determination of micronutrient status would enable either correction for the effects of the acute phase response, or exclusion of subjects with an infection. Exclusion of subjects with an acute phase response has the disadvantage of reducing the use of valuable data, and lessens the comparability to studies that have not screened for acute phase proteins. The application of a correction factor, based on effect sizes such as those reported here, would provide a more elegant solution. The effect size of raised AGP levels on plasma retinol concentrations as found in this study is similar to that reported by Paracha et al. (6 ) even though the prevalence of raised AGP was much higher in that study (51%). Thus, we propose that whenever indicators of micronutrient status are reported, prevalences of raised acute phase protein levels should also be reported. This would enable comparisons of prevalences of micronutrient deficiencies among populations to be made more readily.

The results of this study show that the acute phase response significantly affects plasma concentrations of several commonly used indicators of micronutrient status. Prevalences of deficiencies of vitamin A and of zinc can be overestimated, whereas the prevalence of iron deficiency anemia can be underestimated if the effect of the acute phase response on the plasma concentrations of retinol, zinc and ferritin are not considered. Thus, including measurements of the plasma concentrations of acute phase proteins will improve the assessment of micronutrient status.

	ACKNOWLEDGMENTS

 
We thank all the mothers and the infants, and the health volunteers who participated in this study, and we are grateful for the enthusiastic support we received from the staff of Puskesmas Situ Udik and Cibeungbulang. Furthermore, we thank the field team of Puslitbang Gizi, and the staff from the Bogor laboratory for their untiring efforts. We also thank D.I. Thurnham, J. Coulter and Jen-Shiu Chiang-Chiau from NICHE, University of Ulster for their help with the analysis of retinol, CRP, ACT and AGP.

	FOOTNOTES

 
¹ Financial support for the study was received from:, Dutch Foundation for the Advancement of Tropical Research (WOTRO), Ter Meulen Fund (Royal Netherlands Academy of Arts and Sciences), and UNICEF-Jakarta.

³ Abbreviations used: ACT, ₁-antichymotrypsin; AGP, ₁-acid glycoprotein; CRP, C-reactive protein; MRDR, modified relative dose response.

Manuscript received 4 March 2002. Initial review completed 16 April 2002. Revision accepted 17 July 2002.

	LITERATURE CITED

TOP ABSTRACT INTRODUCTION SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 

1. Filteau, S. M. & Tomkins, A. M. (1994) Micronutrients and tropical infections. Trans. R. Soc. Trop. Med. Hyg. 88:1-3.[Medline]

2. Fleck, A. & Myers, M. A. (1985) Diagnostic and prognostic significance of the acute-phase proteins. Gordon, A. H. Koj, A. eds. The Acute-Phase Response to Injury and Infection 1985:249-271 Elsevier Science Publishers B.V Amsterdam, The Netherlands. .

3. Louw, J. A., Werbeck, A., Louw, M.E.J., Kotze, T.J.V.W., Cooper, R. & Labadarios, D. (1992) Blood vitamin concentrations during the acute-phase response. Crit. Care Med. :934-941.

4. Thompson, S. G., Kienast, J., Pyke, S.D.M., Haverkate, F. & van de Loo, J.C.W. (1995) Hemostatic factors and the risk of myocardial infarction or sudden death in patients with angina pectoris. N. Engl. J. Med. 332:635-641.[Abstract/Free Full Text]

5. Brown, K. H., Lanata, C. F., Yuen, M. L., Peerson, J. M., Butron, B. & Lönnerdal, B. (1993) Potential magnitude of the misclassification of a population’s trace element status due to infection: example from a survey of young Peruvian children. Am. J. Clin. Nutr. 58:549-554.[Abstract/Free Full Text]

6. Paracha, P. I., Jamil, A., Northrop-Clewes, C. A. & Thurnham, D. I. (2000) Interpretation of vitamin A status in apparently healthy Pakistani children by using markers of subclinical infection. Am. J. Clin. Nutr. 72:1164-1169.[Abstract/Free Full Text]

7. Rosales, F. J., Topping, J. D., Smith, J. E., Shankar, A. H. & Ross, A. C. (2000) Relation of serum retinol to acute phase proteins and malarial morbidity in Papua New Guinea children. Am. J. Clin. Nutr. 71:1582-1588.[Abstract/Free Full Text]

8. Mitra, A. K., Alvarez, J. O., Wahed, M. A., Fuchs, G. J. & Stephensen, C. B. (1998) Predictors of serum retinol in children with shigellosis. Am. J. Clin. Nutr. 68:1088-1094.[Abstract]

9. Friis, H., Ndhlovu, P., Kaondera, K., Sandström, B., Michaelsen, K. F., Vennervald, B. J. & Christensen, N. O. (1996) Serum concentration of micronutrients in relation to schistosomiasis and indicators of infection: a cross-sectional study among rural Zimbabwean schoolchildren. Eur. J. Clin. Nutr. 50:386-391.[Medline]

10. Stephensen, C. B. (2001) Vitamin A, infection and immune function. Annu. Rev. Nutr. 21:167-192.[Medline]

11. Dijkhuizen, M. A., Wieringa, F. T., West, C. E., Sri Martuti, & Muhilal, (2001) Effects of iron and zinc supplementation in Indonesian infants on micronutrient status and growth. J. Nutr. 131:2860-2865.[Abstract/Free Full Text]

12. Wieringa, F. T., Dijkhuizen, M. A., West, C. E., Thurnham, D. I., Muhilal, & Van der Meer, J.W.M. (2000) Redistribution of vitamin A after iron supplementation in Indonesian infants. Am. J. Clin. Nutr. in press.

13. Tanumihardjo, S. A., Cheng, J. C., Permaesih, D., Muherdiyantiningsih, , Rustan, E., Muhilal, , Karyadi, D. & Olson, J. A. (1996) Refinement of the modified-relative-dose-response test as a method for assessing vitamin A status in a field setting: experience with Indonesian children. Am. J. Clin. Nutr. 64:966-971.[Abstract/Free Full Text]

14. Dijkhuizen, M. A., Wieringa, F. T., West, C. E., Muherdiyantiningsih, & Muhilal, (2001) Concurrent micronutrient deficiencies in lactating mothers and their infants in Indonesia. Am. J. Clin. Nutr. 73:786-791.[Abstract/Free Full Text]

15. Thurnham, D. I., Smith, E. & Flora, P. S. (1988) Concurrent liquid-chromatographic assay of retinol, -tocopherol, ß-carotene, -carotene, lycopene, and ß-cryptoxanthin in plasma, with tocopherol acetate as internal standard. Clin. Chem. 34:377-381.[Abstract/Free Full Text]

16. Dirren, H., Barclay, D., Ramos, J. G., Lozano, R., Montalvo, M. M., Davila, N. & Mora, J. O. (1994) Zinc supplementation and child growth in Ecuador. Adv. Exp. Med. Biol. 352:215-222.[Medline]

17. Gibson, R. S. (1990) Principles of Nutritional Assessment 1990 Oxford University Press Oxford, UK. .

18. Ruz, M., Solomons, N. W., Meija, L. A. & Chew, F. (1995) Alteration of circulating micronutrients with overt and occult infections in anaemic Guatemalan preschool children. Int. J. Food Sci. Nutr. 46:257-265.[Medline]

19. Stephensen, C. B. & Gildengorin, G. (2000) Serum retinol, the acute phase response, and the apparent misclassification of vitamin A status in the third National Health and Nutrition Examination Survey. Am. J. Clin. Nutr. 72:1170-1178.[Abstract/Free Full Text]

20. Cook, J. D., Skikne, B. S. & Baynes, R. D. (1993) Serum transferrin receptor. Annu. Rev. Med. 44:63-74.[Medline]

21. Beisel, W. R. (1998) Infection-induced depression of serum retino—a component of the acute phase response or a consequence?. Am. J. Clin. Nutr. 68:993-994.[Medline]

22. Mitra, A. K., Alvarez, J. O., Guay-Woodford, L., Fuchs, G. J., Wahed, M. A. & Stephensen, C. B. (1998) Urinary retinol excretion and kidney function in children with shigellosis. Am. J. Clin. Nutr. 68:1095-1103.[Abstract]

23. Stephensen, C. B. (2000) When does hyporetinolemia mean vitamin A deficiency?. Am. J. Clin. Nutr. 72:1-2.[Free Full Text]

24. Weinberg, E. D. (1975) Nutritional immunity. Host’s attempt to withhold iron from microbial invaders. J. Am. Med. Assoc. 231:39-41.[Medline]

25. Oppenheimer, S. J. (2001) Iron and its relation to immunity and infectious disease. J. Nutr. 131:616S-635S.[Abstract/Free Full Text]

26. Christian, P., Schulze, K., Stoltzfus, R. J. & West, K.P., Jr (1998) Hyporetinolemia, illness symptoms, and acute phase protein response in pregnant women with and without night blindness. Am. J. Clin. Nutr. 67:1237-1243.[Abstract]

27. World Health Organization (1996) Indicators for Assessing Vitamin a Deficiency and Their Application in Monitoring and Evaluating Intervention Programmes 1996 WHO Geneva, Switzerland. .

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				S. H. Gieng and F. J. Rosales Plasma {alpha}1-Acid Glycoprotein Can Be Used to Adjust Inflammation-Induced Hyporetinolemia in Vitamin A-Sufficient, but Not Vitamin A-Deficient or -Supplemented Rats J. Nutr., July 1, 2006; 136(7): 1904 - 1909. [Abstract] [Full Text] [PDF]

				C R Wall, C C Grant, N Taua, C Wilson, and J M D Thompson Milk versus medicine for the treatment of iron deficiency anaemia in hospitalised infants Arch. Dis. Child., October 1, 2005; 90(10): 1033 - 1038. [Abstract] [Full Text] [PDF]

				S. E Cusick, J. M Tielsch, M. Ramsan, J. K Jape, S. Sazawal, R. E Black, and R. J Stoltzfus Short-term effects of vitamin A and antimalarial treatment on erythropoiesis in severely anemic Zanzibari preschool children Am. J. Clinical Nutrition, August 1, 2005; 82(2): 406 - 412. [Abstract] [Full Text] [PDF]

				P. J van Jaarsveld, M. Faber, S. A Tanumihardjo, P. Nestel, C. J Lombard, and A. J S. Benade {beta}-Carotene-rich orange-fleshed sweet potato improves the vitamin A status of primary school children assessed with the modified-relative-dose-response test Am. J. Clinical Nutrition, May 1, 2005; 81(5): 1080 - 1087. [Abstract] [Full Text] [PDF]

				C. Duggan, W. B. MacLeod, N. F. Krebs, J. L. Westcott, W. W. Fawzi, Z. G. Premji, V. Mwanakasale, J. L. Simon, K. Yeboah-Antwi, D. H. Hamer, et al. Plasma Zinc Concentrations Are Depressed during the Acute Phase Response in Children with Falciparum Malaria J. Nutr., April 1, 2005; 135(4): 802 - 807. [Abstract] [Full Text] [PDF]

				M. B Zimmermann, L. Molinari, F. Staubli-Asobayire, S. Y Hess, N. Chaouki, P. Adou, and R. F Hurrell Serum transferrin receptor and zinc protoporphyrin as indicators of iron status in African children Am. J. Clinical Nutrition, March 1, 2005; 81(3): 615 - 623. [Abstract] [Full Text] [PDF]

				M. A Dijkhuizen, F. T Wieringa, C. E West, and Muhilal Zinc plus {beta}-carotene supplementation of pregnant women is superior to {beta}-carotene supplementation alone in improving vitamin A status in both mothers and infants Am. J. Clinical Nutrition, November 1, 2004; 80(5): 1299 - 1307. [Abstract] [Full Text] [PDF]

				M. C Tondeur, C. S Schauer, A. L Christofides, K. P Asante, S. Newton, R. E Serfass, and S. H Zlotkin Determination of iron absorption from intrinsically labeled microencapsulated ferrous fumarate (sprinkles) in infants with different iron and hematologic status by using a dual-stable-isotope method Am. J. Clinical Nutrition, November 1, 2004; 80(5): 1436 - 1444. [Abstract] [Full Text] [PDF]

				J. G. Erhardt, J. E. Estes, C. M. Pfeiffer, H. K. Biesalski, and N. E. Craft Combined Measurement of Ferritin, Soluble Transferrin Receptor, Retinol Binding Protein, and C-Reactive Protein by an Inexpensive, Sensitive, and Simple Sandwich Enzyme-Linked Immunosorbent Assay Technique J. Nutr., November 1, 2004; 134(11): 3127 - 3132. [Abstract] [Full Text] [PDF]

				F. T Wieringa, M. A Dijkhuizen, and C. E West Iron and zinc interactions Am. J. Clinical Nutrition, August 1, 2004; 80(3): 787 - 788. [Full Text] [PDF]

				S. Sankaranarayanan, J. Untoro, J. Erhardt, R. Gross, and F. J. Rosales Daily Iron Alone but Not in Combination with Multimicronutrients Increases Plasma Ferritin Concentrations in Indonesian Infants with Inflammation J. Nutr., August 1, 2004; 134(8): 1916 - 1922. [Abstract] [Full Text] [PDF]

				E. J. Hoffenberg, L. M. Emery, K. J. Barriga, F. Bao, J. Taylor, G. S. Eisenbarth, J. E. Haas, R. J. Sokol, I. Taki, J. M. Norris, et al. Clinical Features of Children With Screening-Identified Evidence of Celiac Disease Pediatrics, May 1, 2004; 113(5): 1254 - 1259. [Abstract] [Full Text] [PDF]

				S. A. Tanumihardjo Assessing Vitamin A Status: Past, Present and Future J. Nutr., January 1, 2004; 134(1): 290S - 293. [Abstract] [Full Text] [PDF]

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