Effect of zinc intake on mental and motor development in infants: a meta-analysis

A systematic review and meta-analysis of available randomized controlled trials (RCTs) was conducted to evaluate the effect of zinc (Zn) intake on mental and motor development in infants. Out of 5500 studies identified through electronic searches and reference lists, 5 RCTs were selected after applying the exclusion/inclusion criteria. The influence of Zn intake on mental and motor development was considered in the overall meta-analysis. Other variables were also taken into account as possible effect modifiers: doses of Zn intake, intervention duration, nutritional situation, and risk of bias. Indices of mental and motor development assessed were the Mental Development Index (MDI) and Psychomotor Development Index (PDI). Additionally we carried out a sensitivity analysis. The pooled β was -0.01 (95 %CI -0.02, 0) for MDI and 0 (95 %CI -0.03, 0.02) for PDI, with a substantial heterogeneity in both analyses. When we performed a meta-regression, the effect of Zn supplementation on MDI changed depending on the dose of supplementation. Regarding PDI, there was a differential effect of Zn intake depending on intervention duration, dose of supplementation, nutritional situation, and risk of bias. Zn supplementation showed a negative, weak and significant effect on PDI score in those studies with a length of 4 to 20 weeks (β= -0.05; CI 95 % -0.06 to -0.04). In conclusion, no association was found between Zn intake and mental and motor development in infants. Further standardized research is urgently needed to clarify the role of Zn supplementation upon infant mental and motor development, particularly in Europe.