The study, published in the new issue of The Lancet , adds further evidence to the immune boosting properties of the element, with other trials also showing reduced frequency of pneumonia and diarrhoea in low-income settings.
"This large trial demonstrates that the benefits of zinc supplementation include mortality reduction in addition to the reduction in cases of pneumonia, diarrhoea and malaria that we found in previous trials," said senior author Robert Black from at the Johns Hopkins Bloomberg School of Public Health.
Zinc is one of the most plentiful trace elements in the body, second only to iron.
It mediates many physiological functions and is believed to be essential for maintaining a healthy immune system.
The double-blind, placebo-controlled trial involved 42,546 children (age range 1 to 36 months) living in Pemba, Zanzibar and randomly assigned to receive with daily zinc supplements (10 mg per day, 5 mg in children under 12 months), or placebo for an average of 485 days.
Lead author Sunil Sazawal reports that, while no statistically significant reduction in mortality was observed for the overall population group (seven per cent reduction), amongst the children aged between 12 to 48 months, a statistically significant 18 per cent reduction in mortality was observed.
Possible explanations for this observations, said the researchers, could include infants getting sufficient amounts of zinc in utero and through breast-feeding to sustain them during the first year of life, or may also be a result of the lower doses of zinc given to infants (5 mg) compared to the higher doses given to older children (10 mg).
"Our findings of no effect in infants needs further investigation with existing datasets, and in subsequent studies because they could have important implications for targeting children who would benefit from additional zinc," wrote the authors.
"While further work is needed to evaluate higher dose effects, recommendations for use of zinc as a preventive strategy needs to consider the collective evidence of the effect on growth, morbidity and mortality, which would suggest benefit in children age 6 months and up," said Sazawal.
In an accompanying editorial by Shinjini Bhatnagar from the All India Institute of Medical Sciences in New Delhi said that Sazawal's study raised some important policy issues.
"Could the varying doses of zinc used for these mortality studies have affected the results?" asked Bhatnagar.
"One is tempted to speculate that larger doses than those used in the trial in Zanzibar could be more beneficial in the reduction of mortality than was actually seen.
An obvious lesson is that increased emphasis should be given to studying specific mechanisms by which zinc acts, and whether the benefits are related to correction of zinc deficiency or to favourable effects of zinc at increasing concentrations.
Such knowledge could guide definition of a rationale for a daily optimum dose," said Bhatnagar.
"In the interim, the present WHO strategy to focus on introduction of zinc for treatment of diarrhoea is an important step forward," concluded the editorial.
"In the long-term, measures to improve zinc intake of children, such as improvement of the overall diet, supplementation, food fortification, and sub-selection of crops with improved zinc content need to be explored and assessed."
Source: The Lancet 17 March 2007, Volume 369, Pages 927-934; doi:10.1016/S0140-6736(07)60452-8 "Effect of zinc supplementation on mortality in children aged 1-48 months: a community-based randomised placebo-controlled trial" Authors: S. Sazawal, R.E. Black, M. Ramsan, H.M. Chwaya, A. Dutta, R.J. Stoltzfus, M.K. Othman, F.M. Kabole Editorial: The Lancet 17 March 2007, Volume 369, Pages 885-886 "Effects of zinc supplementation on child mortality" Author: S. Bhatnagar