Depression is the most prevalent mental disorder and a leading cause of global disability, especially in older adults. It is significantly associated with mortality, comorbid disease, and cognitive decline. Â Identifying modifiable risk factors is therefore essential for the prevention of depression. Emerging research links air pollution, particularly fine particulate matter with a diameter of 2.5 micrometers or less (PM2.5), to enhanced risk of depression. PM2.5 contains multiple components with different levels of toxicity, but their individual and combined impacts on depression are not well explored. Previous studies were limited by small sample sizes, conducted outside the U.S., or focused on single PM2.5 components. Therefore, Georgia researchers conducted a national cohort study of US Medicare beneficiaries between January 2000 and 2018 to examine both the combined and individual effects of PM2.5 components on new cases of depression. This study also assesses whether these associations differ by demographic factors and comorbidities.
A total of 23,696,223 (mean age = 76.0±6.4 years, female = 55.2%, male = 44.8%) individuals of ≥65 years were included in this population-based, nationwide cohort study. Among them, 5,544,678 individuals developed depression, whereas 18,151,545 did not. Annual exposure to PM2.5 and six major components, such as sulfate, nitrate, elemental carbon, ammonium, soil dust, and organic carbon, was estimated using high-resolution ensemble models and assigned at the zip-code level. Depression incidence was identified using International Classification of Diseases, Ninth/Tenth Revision (ICD-9/10) codes from Medicare claims, with a 5-year clean period to capture new cases. Quantile g-computation (QGC) and stratified Cox proportional hazards models were employed to investigate the joint and individual pollutant effects, adjusting for relevant covariates and conducting subgroup analysis by comorbidities and demographic factors. All statistical analyses were carried out using R software version 4.2.3.
Single-pollutant analysis reported that a depression was strongly associated with PM2.5 mass (hazard ratio [HR] = 1.02; 95% confidence interval [CI]: 1.01-1.02) and 4/6 of the major components, including soil dust (HR = 1.03; 95% CI: 1.03-1.04), ammonium (HR = 1.01; 95% CI: 1.01-1.02), sulfate (HR = 1.05; 95% CI: 1.04-1.06), and elemental carbon (HR = 1.03; 95% CI: 1.03-1.04). The combined PM2.5 component mixture showed a stronger association with depression compared to PM2.5 mass alone, with each one-quartile rise in the mixture being linked to a higher risk of depression, with an HR of 1.07 (95% CI: 1.06-1.07). QGM analysis further detected elemental carbon (weight = 0.25), soil dust (weight = 0.41), and sulfate (weight = 0.34) as the primary contributors. All these were strongly associated among adults with neurological comorbidities and cardiometabolic disorders.
The study had several limitations, including potential multicollinearity, exclusion of some PM2.5 components, possible misclassification of depression in administrative data, assessment of zip-code-level exposure, and residual confounding.
In conclusion, this study found that long-term exposure to PM2.5, especially elemental carbon, soil dust, and sulfate, was associated with enhanced depression risk, particularly among individuals with comorbidities. These results highlight the need for stronger regulations on PM2.5 emissions, especially from traffic and fossil fuel sources.
References: Deng Y, Hao H, Zhu Q, Liu Y, Steenland K. Exposure to Multiple Fine Particulate Matter Components and Incident Depression in the US Medicare Population. JAMA Netw Open. 2025;8(12):e2551042. doi:10.1001/jamanetworkopen.2025.51042
