Association between hair lead levels and autism spectrum disorder in children: A systematic review and meta-analysis.

A number of studies measured lead levels in hair from children with autism spectrum disorder (ASD) to detect the relationship between cumulated lead exposure and the development of ASD, but results are inconsistent. We aimed to conduct a systematic review and meta-analysis using the published studies to explore the actual association of hair lead levels with ASD in children. We searched PubMed, Embase, PsycINFO, and Cochrane Library databases (up to December 11, 2018). The random-effects model was applied to summarize effect sizes. Subgroup and meta-regression analyses were performed simultaneously. Twenty eligible studies involving 1787 participants (941 autistic children and 846 healthy subjects) were included. Our results of primary analysis showed that there were no statistically significant differences in the levels of hair lead between children with ASD and healthy individuals (Hedges's g = 0.251; 95% confidence interval: -0.121, 0.623; P = 0.187). We identified 2 sources of between-study heterogeneity: analytical technology and the sample size of patients. Additionally, no publication bias was observed in this meta-analysis. In conclusion, this study does not support the association of hair lead levels with ASD in children, and the involvement of cumulated lead exposure in the occurrence of ASD.