Lay Summary

We studied the association between exposure to air pollutants and prescriptions of psychotropic drugs at the individual level in the general population. We found a clear association between exposure to PM2.5 and antipsychotics, antidepressants and mood stabilizers, especially in the age range 30-64 years. The results reinforce the evidence that air pollution is related to mental disorders.

Background

The literature on the adverse effects of long-term exposure to air pollution on mental disorders is still limited. This study aims to investigate the associations between air pollutants and prescriptions of psychotropic drugs at the individual level in a large cohort.

Methods

We enrolled 1,739,277 individuals with 30+ years living in Rome in the 2011 census and followed them up until 31st December 2019. We excluded subjects that at baseline had a prevalent mental disorder, use of specific drugs in the previous 5-year period (antipsychotics, antidepressants and mood stabilizers), and evidence of epilepsy. Furthermore, we assigned annual average concentrations of fine particulate matter (PM2.5), nitrogen dioxide (NO₂), and Black Carbon (BC) to baseline residential addresses. We applied Cox regression models with adjustment for individual and area-level covariates.

Results

This study identified incident cases of antipsychotics (79,362 subjects), antidepressants (200,549 subjects) and mood stabilizers (198,507 subjects) prescriptions. The hazard ratios (for each interquartile range of the pollutants, IQR) were positive and statistically significant for the three main pollutants and the three-drug categories, with stronger effects for PM2.5 (IQR, 1.13 µg/m3) on antipsychotics (HR= 1.038; 95%CI =1.028-1.049), antidepressants (HR= 1.013; 95% CI =1.007-1.019), and mood stabilizers (HR=1.013; 95% CI=1.007-1.019). The effects were generally higher in the age group 30-64 than in the 65+.

Conclusion

Long-term exposure to air pollutants was associated with an increased risk of psychotropic drug prescriptions. The findings increase the credibility of the relationship between air pollution and mental health.