Brown et al (1) have updated a meta-analysis of the effects of zinc supplements on the growth of children in developing countries. The new analysis, which was based on 33 randomized controlled trials, shows a highly significant aggregate effect size of 0.350 (95 percent CI: 0.189, 0.511) for height, 0.309 (95 percent CI: 0.178, 0.439) for weight, and approx= 0 for weight-for-height increments. The previous effort found smaller but significant effects, for example, an effect size of 0.22 for height increments (2). Several factors may explain the differences in effect sizes between the 2 analyses. The inclusion criteria were modified in the most recent analysis and trials lasting <8 wk and that included premature or severely malnourished infants, a total of 9 studies, were omitted. These changes in inclusion criteria are justified and make the findings relevant to nonhospitalized children. Fourteen studies were additions to the second analysis (although 5 were published before 1996, the upper bound of the first analysis), and only 20 were common to both analyses. Both analyses included prepubertal children but the age range was narrower in the second (from 0 to 10 y rather than to 13 y).
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