Association between long-term exposure to low ambient benzene concentrations and mental disorders in the UK: A nested case-control study.

Background: The mental health impacts of long-term ambient benzene exposure remain incompletely understood. We aim to investigate the association between long-term exposure to low-concentration ambient benzene and mental disorders in the general population.

Method: Estimated annual benzene concentrations from UK-wide air pollution maps were linked to health data from 410,605 eligible UK Biobank participants. A nested case-control analysis was performed to assess the risk of all-cause and ten specific mental disorders, using 1:4 risk-set matching with replacement (matching each case to up to four controls). Conditional logistic regression estimated odds ratios (ORs) and 95 % confidence intervals (CIs), and restricted cubic spline models evaluated exposure-response relationships. Subgroup analyses identified potential vulnerable populations.

Results: In fully adjusted models, per interquartile range (IQR) increase in benzene exposure was associated with higher risks of all-cause mental disorders (OR: 1.19, 95 % CI: 1.16-1.23), mood disorders (OR: 1.12, 95 % CI: 1.06-1.19), anxiety disorders (OR: 1.31, 95 % CI: 1.25-1.38), substance use disorders (OR: 1.23, 95 % CI: 1.16-1.31), and sleep disorders (OR: 1.13, 95 % CI: 1.05-1.23). Significant associations were also observed within six subtypes: depressive episodes, panic disorder, phobic anxiety disorder, post-traumatic stress disorder, alcohol use disorder, and tobacco use disorder. Exposure-response curves were predominantly nonlinear, with risks elevated even at low concentrations, suggesting no clear safe threshold. The associations were generally consistent across subgroups, with stronger risks among individuals without hypertension or diabetes.

Limitations: We cannot establish causality.

Conclusion: Long-term exposure to low-level ambient benzene concentrations is associated with increased risks of all-cause and specific mental disorders. These findings provide evidence to inform air pollutant management policy.