News
Zinc supplementation prevents diarrhoea and pneumonia
Gavin Yamey , BMJ
Dietary zinc supplementation reduces the incidence of childhood pneumonia by
41%and the prevalence of diarrhoea by up to 25%according to a systematic
review of 10 randomised controlled trials all performed in the developing
world (Journal of Pediatrics 1999;135:689-97).
This compares favourably with other preventive interventions for diarrhoea,
such as sanitation and breast feeding, and is more effective than any other
intervention to prevent pneumonia.
Zinc deficiency is common in young children in the developing world and is
associated with reduced immunocompetence and increased rates of serious
infectious diseases. Several trials in poor countries have shown the benefit
of zinc supplementation in reducing infection (BMJ 1998;317:369), but these
have varied in the magnitude of the effect and the presence of a differential
effect by age and sex. Some trials were underpowered to detect the effects on
infrequent outcomes, and others remain unpublished.
A pooled analysis was conducted by the Child Health Research Project, a group
of researchers from Johns Hopkins School of Public Health and the World
Health Organisation, who had access to the original trial data. Trials were
included if they provided oral supplements containing at least half the US
recommended daily allowance of zinc for children, and if morbidity
surveillance was carried out for at least four weeks. Two sets of trials were
identifiedthose in which zinc was given continuously, and those giving only a
short course.
For the zinc supplemented children in the seven continuous trials, the pooled
odds ratios for diarrhoeal incidence and prevalence were 0.82 (95%CI 0.72 to
0.93) and 0.75 (0.63 to 0.88) respectively. Supplemented children had an odds
ratio of 0.59 (0.41 to 0.83) for incidence of pneumonia.
No significant variations in the effects were seen in the subgroups of
children stratified by age, sex, and weight, and nor was there a significant
difference between short course and long term supplementation.
The authors conclude that "the development of effective and feasible
interventions to improve the zinc status of developing country populations is
essential." One such intervention, zinc fortification of bread, was shown in
a randomised controlled trial to reduce diarrhoea, respiratory illnesses, and
skin infections in Turkish schoolchildren (Cereal Chemistry 1995;73:424-6).
Dr Robert Black, of Johns Hopkins School of Public Health and co-author of
the study, said: "Zinc fortification is potentially a powerful tool for
settings which produce commercial food, and the idea has been acceptable to
food manufacturers. If there's no commercial food, increasing zinc intake is
possible by reducing the amount of dietary phytates, which interfere with
zinc absorption. This can be done by soaking or fermenting food. Long term,
it is possible that plant breeding could be used to increase zinc or reduce
phytate content."
But several questions still remain before zinc therapy can be incorporated
into diarrhoeal disease control programmes, including the optimal dosing
regime and duration of therapy. Dr Shammim Qazi, from the Division of Child
Health and Development of the World Health Organisation, said: "At present
the WHO is not recommending zinc supplementation as routine. We are waiting
for the results of larger trials, and we are planning a trial ourselves."
The Child Health Research Project's Special Report, Zinc for Child Health, is
at http://ih.jhsph.edu/chr/publicat.htm
© British Medical Journal 1999
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