Effect of zinc intake on serum/plasma zinc status in infants: a meta-analysis

A systematic review and meta-analysis of available randomised controlled trials (RCTs) was conducted to evaluate the effect of zinc (Zn) intake on serum/plasma Zn status in infants. Out of 5500 studies identified through electronic searches and reference lists, 13 RCTs were selected after applying the exclusion/inclusion criteria. The influence of Zn intake on serum/plasma Zn concentration 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 status and risk of bias. The pooled β of status was 0.09 [confidence interval (CI) 0.05 to 0.12]. However, a substantial heterogeneity was present in the analyses (I(2) = 98%; P = 0.00001). When we performed a meta-regression, the effect of Zn intake on serum/plasma Zn status changed depending on the duration of the intervention, the dose of supplementation and the nutritional situation (P ANCOVA = 0.054; <0.001 and <0.007, respectively). After stratifying the sample according to the effect modifiers, the results by duration of intervention showed a positive effect when Zn intake was provided during medium and long periods of time (4-20 weeks and >20 weeks). A positive effect was also seen when doses ranged from 8.1 to 12 mg day(-1). In all cases, the pooled β showed high evidence of heterogeneity. Zn supplementation increases serum/plasma Zn status in infants, although high evidence of heterogeneity was found. Further standardised research is urgently needed to reach evidence-based conclusions to clarify the role of Zn supplementation upon infant serum/plasma Zn status, particularly in Europe.