Effects of micronutrients on growth of children under 5 y of age: meta-analyses of single and multiple nutrient interventions

Background: Micronutrient interventions have received much attention as a cost-effective and promising strategy to improve child health, but their roles in improving child growth remain unclear. Objective: Meta-analyses of randomized controlled trials were conducted to evaluate the effect of micronutrient interventions on the growth of children aged <5 y old. Design: Eligible studies were identified by PubMed database searches and other methods. Weighted mean effect sizes and 95% CIs were calculated for changes in height, weight, and weight-for-height z scores (WHZ) by using random-effect models. Tests for publication bias were done by using funnel plots, heterogeneity, and stratified analyses by predefined characteristics. Results: Interventions including iron (n = 27) or vitamin A (n = 17) only had no significant effects on growth. Interventions including zinc only (n 43) had a small positive effect (effect size = 0.06; 95% CI: 0.006, 0.11) on change in WHZ but no significant effect on height or weight gain. Multiple micronutrient interventions (n = 20) improved linear growth (0.09; 95% CI: 0.008, 0.17). Conclusions: Our findings confirm earlier results of no benefits for interventions including iron and vitamin A only but differ from the earlier meta-analysis that found improvements in linear growth for zinc only interventions. This may be due to the improved nutritional status of children in the more recent studies. Multiple micronutrient interventions improve linear growth, but the benefits are small. Other strategies are needed to prevent stunting. Am J Clin Nutr 2009; 89: 191-203.