Association Between Biological Lead Concentrations and Autism Spectrum Disorder (ASD) in Children: a Systematic Review and Meta-Analysis.

Studies have been conducted in different countries of the world to illustrate a link between autism spectrum disorder (ASD) and lead (Pb) in different specimens such as hair, blood, and urine. Therefore, we carried out a systematic review and meta-analysis to determine the association between Pb concentration in biological samples (blood, urine, and hair) and ASD in children through case-control and cross-sectional studies. In this systematic review, PubMed, Web of Sciences, Scopus, and Google Scholar were searched for relevant studies from January 2000 to February 2022. A random-effects model was used to pool the results. The effect sizes were standardized mean differences (proxied by Hedges' g) followed by a 95% confidence interval. Pooling data under the random effect model from blood and hair studies showed a significant difference between the children in the ASD group and the control group in blood lead level (Hedges' g: 1.21, 95% CI: 0.33-2.09, P = 0.01) and hair level (Hedges' g: 2.20, 95% CI: 0.56-3.85, P = 0.01). For urine studies, pooling data under the random effect model from eight studies indicated no significant difference between the children in the ASD group and control group in urinary lead level (Hedges' g: - 0.34, 95% CI: - 1.14,0.45, P = 0.40). Moreover, the funnel plot and the results of the Egger test for the blood and urine samples showed no publication bias, while, for the hair samples, the funnel plot illustrated the existence of publication bias.