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Print version ISSN 0042-9686
Bull World Health Organ vol.80 n.2 Genebra Jan. 2002
African children talk faster with iron
The first trial in Africa of the effect of dietary iron supplements on child development has shown that they speed language learning in under-three-year-olds and to a lesser extent improve motor skills.
Rebecca Stoltzfus of Johns Hopkins University School of Public Health, lead author of the study (BMJ 2001; 323: 1389), which was undertaken in Pemba Island in the Zanzibar archipelago, told the Bulletin that while the supplements had little effect on the high levels of anaemia (a reduction in haemoglobin) in the children, "we did correct iron deficiency, and that makes the impact on child development even more interesting".
The issue is that intense and year-round transmission of malaria in Pemba, as in most of sub-Saharan Africa, also contributes to anaemia in young children along with other causes apart from iron-deficient diets. But, says Stoltzfus, "our results indicate that even in situations where iron alone can't correct anaemia, it can have significant benefit for development."
"Biologically it makes some sense" said Stoltzfus, as there's "very strong evidence" in animals that the level of iron in the body can affect nerve development. Two key nervous processes are affected by iron. One is myelination, the development of the sheaths that help nerve signals travel rapidly. "That process continues after birth in humans" said Stoltzfus, "and iron is involved in the enzyme systems that build the sheaths." The other process affected by iron is in the dopamine system of neurotransmission across the synapses or junctions between cells. "That's been well described in animals" Stoltzfus said. Moreover "a group in Chile has documented that iron-deficient children transmit auditory signals and process them less rapidly, consistent with inferior myelination of those nerves".
In Pemba, iron supplements also improved motor skills, as this theory would imply as such skills are also a matter of nerves but here the benefit was very dependent on the severity of the children's anaemia. With the language skills, all children benefited, but in motor skills only children with initial haemoglobin below 9 g/l improved. "But in Pemba half the kids are down there so it's a significant number" said Stoltzfus.
The most controversial point in the study may be the actual measure of the improvement of language skills, based on a questionnaire to parents.
"We used this measure because it was simple and could be managed by field workers not trained as psychologists" said Stoltzfus. "Jane Kvalsvig, Director of the Child Development Programme at the University of Natal in South Africa, developed a scale based on parental reports. So we said let's try it. And our feeling about the scale was that it probably was not a highly sensitive instrument we were measuring gross and global milestones that would be noticed by parents. So if there were subtle influences on the brain that didn't manifest in gross milestones we wouldn't have detected them. So the fact that we did see changes was quite striking."
According to Bruno de Benoist, responsible for micronutrients at WHO, "The problem is to develop specific psychometric tests that can be applied to these cultures and populations. It's a huge limitation. But if their tests are acceptable it is a very significant result, to show an improvement of intellectual performance."
"In terms of numbers of people affected," said de Benoist, "iron is the most important micronutrient deficiency (followed by vitamin A and iodine). And while we have a lot of data on anaemia, we have a lot less on iron itself for the simple reason that it is very difficult to measure. So the more results we have the better we will understand the effects of iron deficiency."
"Say we know now that iron deficiency affects cognitive development," said de Benoist. "But to what extent? And what kind of prevention and treatment can we give the child? And what is the magnitude of the cognitive effects of iron deficiency in the population as a whole? That's very important, because there are many other causes of poor cognitive development."
Stolztfus and her colleagues will now aim to confirm their findings. "I think that our study is provocative: it was a well-done, well-organized randomized clinical trial with all the things that we look for in proving causality statistical significance, good design and all of that" she claimed. "But we ourselves would like to replicate and extend the results. So we are studying again in Pemba, with a larger group and choosing just the younger children, where the effect was seen, and doing a parallel study in rural Nepal, where malaria is less but iron deficiency is high."
Robert Walgate, Bulletin