Estimating the causal effect of air pollution on mental disorders: A two-sample Mendelian randomization study

Background

Observational studies have reported a link between particulate matter 2.5 (PM_2.5) and the risk of mental disorders; however, the causality is unclear.

Methods

Using publicly available genome-wide association studies, we conducted a two-sample Mendelian randomization (MR) study to assess the causal relationship between PM_2.5 and six mental disorders: attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), bipolar disorder (BD), major depressive disorder (MDD), schizophrenia (SCZ), and anxiety disorder (ANX). The inverse-variance weighting method was used as the main method for estimating causal effects. MR-Egger, weighted median, simple mode, weighted mode, and MR-PRESSO were applied as supplementary analyses.

Results

Using the inverse-variance weighting method, genetically predicted PM_2.5 exposure increased the risk of ADHD (odds ratio [OR] = 1.52, 95% confidence interval [CI] = 1.16 to 1.99, p = 0.002), ANX (OR = 2.96, 95% CI = 1.29 to 6.81, p = 0.01), and SCZ (OR = 2.21, 95% CI = 1.40 to 3.47, p = 0.001). However, there was no evidence to suggest that genetically predicted exposure to PM_2.5 increased the risk of the other three mental disorders (p > 0.05).

Conclusions

The present findings enhance our understanding of the role of PM_2.5 exposure on ADHD, ANX, and SCZ risk. It may be necessary to search for novel components with neuroprotective effects to provide new preventive and therapeutic strategies for PM_2.5-induced brain damage.