Highlights
- Long-term residential exposure to fine particulate matter (PM2.5, PM10) and nitrogen oxides (NOx) is linked to increased risk of antidepressant medication dispensing in women, but not men.
- Road traffic noise shows a potential, though statistically weaker, association with antidepressant use in women, suggesting a complex interaction between noise exposure and mental health.
- Findings support targeting environmental exposures, especially air quality improvements, as a potential avenue to reduce depressive symptom burden.
- Sex-specific susceptibility underscores the need for tailored public health interventions and further mechanistic research on gender differences in depression pathophysiology.
Background
Depression is a major contributor to global disability, with growing evidence implicating environmental factors, including air pollution and noise, as modifiable risks. The pathophysiological links between exposure to ambient pollutants, traffic-related noise, and depressive symptomatology remain incompletely understood. While some epidemiological studies suggest a relationship between these exposures and depression or antidepressant use, inconsistencies persist, especially regarding sex differences and specific pollutant types. Given the widespread exposure to urban air pollution and traffic noise worldwide, clarifying their roles in mental health outcomes is critical for informing public health policy and preventive strategies.
Key Content
Chronological Development of Evidence
Recent years have seen an expansion in large-scale cohort studies examining environmental exposures and mental health. Notably, a 2023 longitudinal cohort study in Rome demonstrated positive associations between PM2.5 and nitrogen dioxide exposure and the incidence of depression, schizophrenia spectrum, and anxiety disorders (+7% to +13% hazard ratios per interquartile concentration increase). This study also linked pollutant exposure with increases in psychotropic medication prescriptions, reinforcing biologic plausibility.
Building upon this, the 2025 Swedish Malmö Diet and Cancer Study cohort (Lu et al.) specifically assessed the relationship of long-term exposure to PM2.5, PM10, NOx, and road traffic noise (Lden) with first-time dispensing of antidepressants and/or clinical depression diagnosis during follow-up (2007–2011). Importantly, this study employed rigorously modeled annual mean exposures and adjusted for sociodemographic, lifestyle, and clinical confounders, enhancing causal inference.
Sex-Specific Associations and Effect Size
Lu et al. found statistically significant increased hazard ratios for antidepressant dispensing per 10 µg/m³ increase in PM2.5 (HR 1.29; 95% CI, 1.09–1.52), PM10 (HR 1.10; 1.03–1.17), and NOx (HR 1.15; 1.04–1.26) exclusively in women, but not men. Road traffic noise (per 10 dB increase in Lden) showed a non-significant trend towards increased risk in women (HR 1.06; 95% CI, 0.99–1.13) with no association in men. These lag1-5 exposure windows (1–5 years prior to outcome) and two-pollutant models yielded consistent effect patterns.
The sex discrepancy aligns with prior reports indicating women’s heightened susceptibility to environmental stressors influencing neuroendocrine and inflammatory pathways involved in depression. The relatively stronger effect size for finer particles (PM2.5) suggests that smaller particulate matter, capable of eliciting systemic oxidative stress and neuroinflammation, may be particularly relevant in mood disorder pathogenesis.
Mechanistic Insights
Mechanistic studies suggest that inhaled fine particles and nitrogen oxides promote systemic inflammation, oxidative stress, and neuroinflammation via blood-brain barrier disruption, microglial activation, and altered neurotransmitter systems, which may contribute to depressive symptoms. Noise exposure potentially induces chronic stress responses through hypothalamic-pituitary-adrenal (HPA) axis activation and sleep disturbances, compounding vulnerability.
Further sex-specific mechanistic exploration is warranted given hormonal modulation of stress and immune responses potentially mediating greater female susceptibility.
Limitations and Methodological Considerations
Both cited cohort studies faced limitations such as residual confounding by unmeasured factors (e.g., occupational exposures, genetic predispositions), potential exposure misclassification despite sophisticated modeling, and outcome definitions relying on antidepressant dispensing and medical diagnoses, which may underestimate subclinical cases. The lack of significant findings in men raises questions about sex differences in health-seeking behavior, medication adherence, or differential biological sensitivity.
Additionally, road traffic noise effects showed less consistent statistical strength, possibly due to measurement challenges, lower exposure variance, or confounding by urban socioeconomic factors.
Expert Commentary
The cumulative evidence from these rigorous epidemiological studies supports a compelling association between ambient air pollution and depressive symptomatology, particularly in women. This aligns with a growing environmental psychiatry paradigm emphasizing the detrimental impact of urban stressors on mental health.
Clinical guidelines do not yet routinely consider environmental exposures in depression risk assessment; however, these findings may inform integrated preventive strategies. Environmental policy targeting reduction in fine particulate matter and nitrogen oxides could confer mental health benefits alongside cardio-respiratory gains.
The sex-specific vulnerability observed underscores the importance of personalized risk modification interventions and highlights a gap in understanding sex-dependent neuroimmune mechanisms.
Future research should prioritize longitudinal studies with granular exposure assessments, explore biological mediators including inflammatory biomarkers, and examine interactions with genetic predisposition and psychosocial stressors.
Conclusion
The study by Lu et al. significantly advances the evidence base linking long-term air pollution exposure to increased antidepressant use, particularly in women, reinforcing the hypothesized environmental contributions to depression. Road traffic noise presents a suggestive but less robust association. These findings advocate for environmental health strategies targeting air quality improvements as part of comprehensive mental health promotion.
Continued interdisciplinary research integrating epidemiology, neurobiology, and environmental science is essential to elucidate mechanisms, address sex differences, and translate findings into effective public health interventions reducing the global burden of depressive disorders.
References
- Lu SSM, Ekbäck E, Sommar JN, et al. Long-term exposure to air pollution and road traffic noise in relation to dispensed antidepressant medications: A Swedish cohort study. Environ Res. 2025 Nov 15;285(Pt 2):122435. doi:10.1016/j.envres.2025.122435. PMID: 40713997.
- Cesaroni G, et al. Long-term exposure to air pollution and incidence of mental disorders. Environ Int. 2023 Nov;181:108302. doi:10.1016/j.envint.2023.108302. PMID: 37944432.
- Block ML, et al. The outdoor air pollution and brain health initiative: action to protect children’s neurological development. Lancet Neurol. 2022;21(3):253-256. doi:10.1016/S1474-4422(22)00003-0.
- Power MC, et al. Air pollution and dementia: A systematic review. J Alzheimers Dis. 2016;52(1):212-26. doi:10.3233/JAD-150884.
