Lead exposure and intellectual disability in children : a meta-analysis

Abstract

Background In response to the speculation of parents whose children having elevated blood lead level (BLL) amid the incident of lead-tainted water in Hong Kong that lead exposure may cause intellectual disability (ID) to their children, a study of meta-analysis was carried out to investigate whether the causal inference hypothesized from the speculation is true. Methods The present study followed the reporting checklist proposed by the Meta-analysis of Observational Studies in Epidemiology (MOOSE) Group. Keywords search for eligible studies regarding lead exposure and children with ID was conducted on the databases, namely Pubmed, Cochrane Library, Medline and China Journal Net (中國期刊全文數據庫) respectively. Results Nine case-control studies and two cross-sectional studies were identified from different databases for the analysis. The pooled estimate of mean BLL demonstrated that the mean BLL in the children with ID of unknown etiology was significantly higher than that of the normal children of the control group (4.46 μg/dL, 95% CI =2.114, 6.806, P = 0.000). The difference of mean BLL between the two studied groups of children might imply that the relation between lead exposure and ID in children is causal. The inference supported by the pooled estimate was favoured by the results of the analyses using negative control outcomes, but was refuted by the results of the analyses using negative control exposure. Conclusion The causal inference of lead exposure and ID in children could not be concluded by the present study due to the opposite evidences resulting from the analyses of negative control exposure and outcome.