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Letters to the Editor |
Hugh Sinclair Unit of Human Nutrition Department of Food Science and Technology The University of Reading Whiteknights, Reading RG6 6AP United Kingdom E-mail: a.f.walker{at}afnovell.reading.ac.uk
Dear Sir:
Our study (1) was concerned with the effects of zinc supplementation on the growth and infection rate of 153 Ugandan children in 3 nursery schools. The children, in whom the prevalence of stunting was high, were randomly assigned to receive either fruit juice with 10 mg supplemental Zn/d or fruit juice with placebo on each school day for 8 mo.
A positive growth response was shown for children in only 1 of the 3 schools. This school catered to children of families with moderate incomes. In the 2 schools affordable to families of lower socioeconomic status, the children showed no growth response to zinc supplementation. We suggested that a deficiency of nutrients other than zinc may have accounted for the lack of response in these 2 schools and in similar studies that reported a lack of growth response to zinc supplementation.
The study by Ronaghy et al (2) mentioned by Sandstead involved 49 Iranian boys aged 13 y and bears some similarities to ours, but also some important differences. We were interested at the outset in determining whether, within the context of the diet consumed by young children in Uganda, a modest daily zinc supplement would be effective in combating the exceptionally high prevalence of stunting in that country. Hence, unlike Ronaghy et al, we did not consider adding supplements of energy and protein in an attempt to ensure dietary adequacy of macronutrients. Even if we had done so, as these authors pointed out for the children in their own study, there would have been no guarantee that the modest supplement of 127 kcal energy/d (531 kJ/d) used by Ronaghy et al would have resulted in an adequate energy intake for all the malnourished children in our study.
In hindsight, a design feature of the Iranian study that would have improved our Ugandan study was that all children were given a supplement of nonzinc vitamins and minerals to ensure that dietary targets for these nutrients were met during zinc supplementation. However, our findings were unexpected. We had not been alerted to the importance of nonzinc nutrient status in the growth response of children to zinc supplementation from previous reports.
In the Iranian study, all children were provided with a full spectrum of nonzinc vitamins and minerals, except magnesium. If nutrients are administered in future studies, it would be prudent to include magnesium. This is because magnesium and zinc deficiencies are type 2 deficiencies (3), sharing the following common features: 1) there are no body stores of the nutrients, 2) the body avoids tissue desaturation and uses conservation mechanisms early in the deficiency, and 3) in children, reduction of growth rate is an adaptive mechanism to reduce demands for the nutrients. Magnesium intakes fail to reach nutritional targets in many children (4) and adults (5) in the United Kingdom and other Western countries and a similar situation is likely in the diet of young children fed refined cereals such as maize, which is eaten widely in Uganda. Unfortunately, few studies of malnourished populations have focused on this nutrient.
I am grateful to Sandstead for highlighting this issue. Clearly, more research is warranted to determine the value of zinc supplementation in the growth of children in studies designed to ensure the absence of deficiencies of other vitamins and minerals, including magnesium.
REFERENCES
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