Children at risk of malaria are more likely to die of the disease if they are given dietary supplements of iron and folic acid, according to a study in the latest issue of The Lancet.
The researchers who carried out the study say the World Health Organization (WHO) needs to revise its guidelines on iron supplements as a result of their findings.
The WHO says all children in areas where anaemia is a problem should be given the supplements. Anaemia is a blood disease that can stunt mental and physical development and is usually caused by eating too little iron.
But this has been controversial as some research suggests that iron deficiency can protect against malaria.
Robert Black of Johns Hopkins University, United States, and colleagues gave more than 24,000 Tanzanian children under three either a placebo or a supplement of iron and folic acid every day for a year and a half.
The study showed that only children who had anaemia because of iron deficiency benefited from the supplement.
Generally, however, children receiving iron and folic acid had a 12 per cent greater risk of being hospitalised or dying. The difference was big enough to make the researchers end the trial early.
A parallel trial also published in The Lancet last week showed that in Nepal, where malaria is rare, infants who received the supplements were no more likely to die than those who did not.
Putting the two studies together, Black's team concludes that iron deficient and anaemic children can benefit from the supplements as long as there are active programmes in place to detect and treat malaria and other infections.
But they warn that giving the supplements to infants who are not iron deficient would be harmful.
"Such studies are rare and the study teams are to be applauded," write Mike English and Robert Snow of the Kenya Medical Research Institute and Wellcome Trust Collaborative Programme, in an accompanying article in The Lancet.
Both papers "are far superior to any previous examination of the survival benefits and risks of supplementation with iron and [folic acid]", they add.
English and Snow say the risks associated with giving the supplements to children exposed to malaria "seem to outweigh any immediate benefits".
Anaemia is widespread in the developing world and is especially common in children younger than five years.
Link to full paper in The Lancet (Tanzania)
Reference: The Lancet 367, 133 (2006)
Link to full paper in The Lancet (Nepal)
Reference: The Lancet 367, 144 (2006)
Link to full article by English and Snow in The Lancet
Reference: The Lancet 367, 90 (2006)