Association of secondhand smoke exposure with the risk of autism spectrum disorder: a systematic review and meta-analysis

Objective  To explore the association of secondhand smoke exposure with the risk of autism spectrum disorder (ASD) through a meta-analysis based on observational studies, so as to explore the key exposure windows of the association between secondhand smoke and ASD risk.

Methods  Ovid, EMBASE, Web of Science, Cochrane Library, PubMed, Chinese National Knowledge Infrastructure, and WanFang Database were searched from the establishment of the database to April 30, 2023 for studies investigating the relationship between secondhand smoke exposure and the risk of ASD. Quality assessment was performed on the literature, and evidence strength was evaluated by the Grading of Recommendations, Assessment, Development, and Evaluation(GRADE), and the Best Evidence Synthesis method (BES). The meta-analysis was conducted through a random-effect model or fixed-effect model depending on heterogeneity result.

Results  Thirty-six observational studies were included in this study. The meta-analysis showed that secondhand smoke exposure in the prenatal period and after 1 year of age was associated with the risk of ASD (in the prenatal period: odds ratio OR=1.79, 95% confidence interval CI: 1.20-2.68; after 1 year of age: OR=1.39, 95% CI: 1.10-1.75), but both with low evidence strength. The subgroup analysis detected no heterogeneity. The sensitivity analysis showed stability of the result. The trim-and-fill analysis indicated the possibility of publication bias in the data on the overall exposure period of the exposure group obtained via questionnaires/reports/interviews.

Conclusion  Secondhand smoke exposure in the prenatal period and after 1 year of age might increase the risk of ASD in offspring, and no association with ASD was found at other times. However, limited by the low strength of evidence, high-quality studies are needed to verify this association in the future.