| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
LETTERS TO THE EDITOR |
Department of Public Health and Clinical Medicine
Epidemiology and Public Health Science
Umeå University
S-901 87 Umeå
Sweden
E-mail: torbjorn.lind{at}epiph.umu.se
International Maternal and Child Health (IMCH)
Department of Women's and Children's Health
Uppsala University
SE-751 85 Uppsala
Sweden
E-mail: lars-ake.persson{at}kbh.uu.se
Department of Nutrition
University of California
One Shields Avenue
Davis, CA 95616
E-mail: bllonnerdal{at}ucdavis.edu
Dear Sir:
In their letter, Wieringa et al raise questions concerning definitions of iron and zinc deficiency and interpretation of interactions in the case of combined iron and zinc supplementation. The definitions of anemia, iron deficiency, zinc deficiency, and iron deficiency anemia (IDA) used in articles by Dijkhuizen et al (1) and us (2) are a hemoglobin concentration < 110 g/L, a serum ferritin concentration < 12 µg/L, a serum zinc concentration < 10.7 µmol/L, and a combination of anemia and low serum ferritin, respectively. These cutoffs comply with those suggested by the World Health Organization for anemia, iron deficiency, and IDA (3), whereas the cutoff for zinc deficiency was chosen as the value for serum zinc concentration 2 SDs below the mean for adult persons sampled in the morning after an overnight fast (4). One should remember that these definitions do not imply functional consequences. There are few population-based studies on normal serum zinc concentrations in infants and children. The only 2 studies published to our knowledge suggest a 2.5 percentile at 9–10 µmol/L (5, 6). Thus, both the study by Dijkhuizen et al (1) and our study (2) may have overestimated the problem of zinc deficiency in the populations studied. In addition, the use of serum zinc concentrations in the estimation of zinc status is not optimal, although it has been suggested to be of value in the estimation of zinc status in groups (7). In our study, only single supplementation with iron improved anemia. Both the iron-only supplement and the combined iron and zinc supplement decreased IDA prevalence, although the definition of IDA mentioned above must be pointed out here. Although the iron-only supplement improved both hemoglobin and serum ferritin concentrations, the combined iron and zinc supplement increased only serum ferritin concentrations but had no effect on hemoglobin concentrations in comparison with placebo. From a physiologic point of view, it must then be argued which iron-status measure more accurately depicts improved iron status. We argue that although an increase in hemoglobin concentration shows that ingested iron has in fact been absorbed and used for production of hemoglobin, an increase in only serum ferritin concentration says little about actual improvement of iron status.
Of greater importance to the issue of whether iron supplementation affects zinc status or vice versa are the functional consequences of zinc and iron deficiency. In the second part of our Indonesian study to be published in a forthcoming article (8), we found that combined supplementation with iron and zinc had a significant antagonistic effect on weight gain in Indonesian infants. The interpretation of this result is that adding iron to zinc abolishes the positive effect of zinc supplementation on weight gain. In the same article, we also found that combined supplementation with iron and zinc had a significant negative effect of interaction on psychomotor development, and the interpretation of this result is that adding zinc to iron abolishes the positive effect of iron supplementation on infant psychomotor development. From a public health point of view, these findings are more important than whether iron and zinc supplementation affects the prevalence of suboptimal micronutrient status.
As Wieringa et al suggest, several levels of interaction are possible: from competition for absorptive pathways in the intestine to differences in compliance due to side effects of the combined supplement. From our data, we can determine only that an interaction has occurred, but not which type of interaction is most important. Because of the negative functional consequences, we believe that our conclusion that combined iron and zinc supplementation administered as in the studies by both Dijkhuizen et al (1) and us (2) cannot be routinely recommended remains valid. However, both iron deficiency and zinc deficiency remain important public health problems in low-income settings, and finding solutions to improve iron and zinc nutrition in vulnerable groups, such as infants, children, and pregnant women, remains imperative.
REFERENCES
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
