Study Links Specific Air Pollution Components to Increased Depression Risk in Older Adults

Findings from a nationwide study of US Medicare beneficiaries suggest that prolonged exposure to fine particulate air pollution may increase the risk of depression among older adults, with certain pollution components posing a greater threat than others.

The findings indicate that regulating specific air pollution components, rather than focusing solely on overall particle levels, may help lower depression risk—especially among medically vulnerable groups.

Depression is the most common mental disorder worldwide and a leading cause of disability, accounting for more than 56 million disability-adjusted life years globally in 2021. Among older adults, depression is associated with cognitive decline, physical comorbidities, increased mortality, and substantial social and economic burden. Identifying modifiable risk factors is therefore critical to prevention efforts.

Although prior research has consistently linked fine particulate matter (PM2.5) exposure to depression, PM2.5 is not a single substance. It is a complex mixture of chemical components—including sulfate, elemental carbon, ammonium, nitrate, organic carbon, and soil dust—that originate from diverse sources and vary in toxicity. Until now, the relative contributions of these individual components, and their combined effects, have remained poorly understood.

To address this gap, researchers conducted a nationwide, population-based cohort study using Medicare data from January 2000 through December 2018. The analysis included nearly 23.7 million adults aged 65 years or older who were continuously enrolled in fee-for-service Medicare and lived in the contiguous United States. Participants were followed for the development of late-life depression, identified through Medicare claims.

Over the study period, more than 5.5 million participants developed depression. In single-pollutant models, long-term exposure to PM2.5 mass was associated with a modest but statistically significant increase in depression risk.

However, several individual PM2.5 components showed stronger associations. Sulfate exposure was linked to a 5% increased risk of depression, while elemental carbon and soil dust were each associated with a 3% increased risk. Ammonium exposure was also positively associated, though to a lesser degree.

“Sulfate, a secondary inorganic aerosol mainly from fossil fuel combustion, commonly exists as (NH4)2SO4, NH4HSO4, or sulfuric acid,” the authors wrote. “It may contribute to depression by inducing mitochondrial dysfunction38 and oxidative stress that affect the central nervous system.”

When researchers examined exposure to multiple PM2.5 components simultaneously, the effects were even more pronounced. Each one-quartile increase in the mixture of major PM2.5 components was associated with a 7% higher risk of depression—substantially greater than the association observed for PM2.5 mass alone. Advanced modeling identified soil dust, sulfate, and elemental carbon as the dominant contributors to this increased risk.

Importantly, the associations between PM2.5 components and depression were stronger among individuals with cardiometabolic and neurologic conditions, including cardiovascular disease, diabetes, and dementia. These findings suggest that older adults with preexisting health conditions may be especially susceptible to the mental health effects of air pollution.

REFERENCES

1. Deng Y, Hao H, Zhu Q, et al. Exposure to multiple fine particulate matter components and incident depression in the US Medicare population. JAMA Netw Open. December 22, 2025. doi:10.1001/jamanetworkopen.2025.51042

2. Phend C. Air pollution linked to depression. MedPage Today. December 22, 2025. Accessed December 23, 2025. https://www.medpagetoday.com/geriatrics/depression/119143