Association between exposure to air pollutants and attention-deficit hyperactivity disorder (ADHD) in children: a systematic review and meta-analysis

Recent studies have reached mixed conclusions regarding the association between exposure to air pollutants and attention-deficit hyperactivity disorder (ADHD). We performed systematic review and meta-analysis to determine whether air pollutants were risk factors for the development of ADHD in children. We systematically searched databases for all relevant studies up to 2 July 2019. Together, the studies indicated that exposure to PAHs (risk ratio (RR): 0.98, 95% confidence interval (CI): 0.82–1.17), NOx (RR: 1.04, 95% CI: 0.94–1.15), and PM (RR: 1.11, 95% CI: 0.93–1.33) did not have any material relationship with an increased risk of ADHD. Heterogeneity of study data was low (I2: 2.7%, P = 0.409) for studies examining PAHs, but was substantial for NOx and PM (I2: 68.4%, P = 0.007 and I2: 60.1%, P = 0.014, respectively). However, these results should be interpreted with caution since the number of epidemiological studies investigating this issue were limited.