Preconception and gestational versus postnatal exposure to air pollutants and risk of autism spectrum disorder: a systematic review and meta-analysis

The rising prevalence of ASD has prompted extensive research into potential environmental risk factors, with air pollution particularly emerging as a major concern. A systematic review and meta-analysis on the effect of air pollutants and time of exposure (particularly, PM_2.5, PM₁₀, NO₂, and O₃) and the risk of ASD was therefore performed.

Following PRISMA guidelines and PROSPERO registration (Ref: CRD42023464592), a thorough literature search was conducted across multiple databases, including Scopus, PubMed/MEDLINE, Embase, PsycINFO, Web of Science, and Cochrane Library. The analysis included 27 studies encompassing 369,460 participants, 47,973 of whom were diagnosed with ASD.

Preconception exposure to air pollutants showed a protective trend for PM_2.5, PM₁₀, and O₃ with a 10%, 5%, and 19% reduced risk of ASD, whereas NO₂ had a 28% higher likelihood of ASD. During gestation, PM_2.5 exposure increased ASD risk by 15%, with 13% and 9%, 25% and 7%, and 25% and 10% increases in ASD risk with PM_2.5 and NO₂ for the first, second, and third trimesters, respectively. In the first year of life, 20%, 8%, 33%, and 14% increases in risk were found for PM_2.5, PM₁₀, NO₂, and O₃, respectively, while such risk estimates increased to 179%, 60%, 12%, and 179% for the second year of life.

In this meta-analysis, the relationships between air pollutants and ASD risk revealed significant associations, particularly for PM_2.5 and NO₂. Exposure during preconception exhibited a protective trend, while postnatal exposure, particularly during the second year of life uncovered substantially higher ASD risk.