Environmental pollutants as risk factors for autism spectrum disorders: a systematic review and meta-analysis of cohort studies

Abstract

Background: Autism Spectrum Disorder (ASD) is a lifelong neurodevelopmental condition affecting communication, social interaction, and behavior. Evidence suggests that environmental pollutants are associated with ASD incidence. This review aimed to analyze the effect of environmental pollutants on ASD.

Methods: Systematic review and meta-analysis of cohort studies evaluated the association between exposure to environmental pollutants and ASD. We searched COCHRANE CENTRAL, MEDLINE, CINAHL, LILACS, EMBASE, PsycINFO, Web of Science, SciELO, and gray literature from inception to January 2023. The model used for meta-analysis was inverse variance heterogeneity (IVhet). The effect measures were the beta coefficient (β) and the relative risk (RR) with their 95% confidence intervals (95% CI). Sensitivity analyses were carried out using an instrument to screen or diagnose autism.

Results: A total of 5,780 studies were identified; 27 were included in the systematic review, and 22 were included in the meta-analysis. These studies included 1,289,183 participants and 129 environmental pollutants. Individual meta-analyses found a significant association between nitrogen dioxide RR = 1.20 (95% CI: 1.03 to 1.38; I²: 91%), copper RR = 1.08 (95% CI: 1.03 to 1.13; I²: 0%), mono-3-carboxy propyl phthalate β = 0.45 (95% CI: 0.20 to 0.70; I²: 0%), monobutyl phthalate β = 0.43 (95% CI: 0.13 to 0.73; I²: 0%) and polychlorinated biphenyl (PCB) 138 RR = 1.84 (95% CI: 1.14 to 2.96; I²:0%) with ASD. Subgroup meta-analyses found a significant association with carbon monoxide RR = 1.57 (95% CI: 1.25 to 1.97; I²: 0%), nitrogen oxides RR = 1.09 (95% CI: 1.04 to 1.15; I²: 34%) and metals RR = 1.13 (95% CI: 1.01 to 1.27; I²:24%).

Conclusion: This study found positive associations nitrogen dioxide, copper, mono-3-carboxypropyl phthalate, monobutyl phthalate, and PCB 138, and the development of ASD, likewise, with subgroups of pollutants carbon monoxide, nitrogen oxides, and metals. Therefore, it is important to identify these risk factors in children and adolescents to contribute to ASD and identify prevention strategies effectively.

Keywords: Autism; Cohort studies; Environmental pollutants; Systematic review.