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A national cohort study of long-term exposure to PM2.5 trace element components and depression in older adults in the USA

Nature Mental Health volume 4, pages 377–386 (2026)Cite this article

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Abstract

Given the increasing concerns about the mental health impacts of environmental pollutants, fine particulate matter (PM2.5) is notably significant due to its widespread presence and potential neurological effects. However, research exploring the association between PM2.5-bound trace elements and depression remains sparse. This nationwide cohort study investigates the long-term effects of exposure to PM2.5 metal components—specifically copper (Cu) and zinc (Zn)—on depression among older US adults, analyzing data from over 30 million Medicare beneficiaries spanning 2000 to 2018. Our findings reveal a strong link between extended exposure to PM2.5-bound Cu and Zn and higher depression risks, with the most significant effects observed among all studied metals. These two metals consistently showed the strongest associations across multiple models. Specifically, exposure to Cu and Zn, primarily from non-tailpipe sources such as brake and tire wear, was associated with increased depression rates of 3.5% and 2.2%, respectively, in individuals aged 65 years and older. These results underscore the necessity for targeted public health interventions and policies that address the mental health impacts of specific environmental contaminants, especially in vulnerable populations such as the elderly, and highlight the importance of considering environmental factors within the broader context of mental health and aging.

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Fig. 1: PM2.5 trace element components.
Fig. 2: Averaged chemical composition of PM2.5.
Fig. 3: HRs of depression associated with an IQR increase in 1-year prior exposure to PM2.5 total mass and its trace element components, including Br, Ca, Cu, Fe, K, Ni, Pb, Si, V and Zn.
Fig. 4: Concentration–response curves for 10 PM2.5 trace element components and depression, derived from single-component models.

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Data availability

Medicare claims data used in this study (Medicare Chronic Conditions Warehouse (CCW) and Medicare Denominator File) are available from the US Centers for Medicare and Medicaid Services (CMS) but are not publicly available due to privacy and confidentiality restrictions. Researchers can apply for access through the CMS Data Request Center (https://resdac.org/cms-data/request/cms-data-request-center). PM2.5 total mass and trace element component concentration data are publicly available from the NASA Socioeconomic Data and Applications Center (SEDAC) at https://sedac.ciesin.columbia.edu.

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Acknowledgements

We thank the Centers for Medicare and Medicaid Services for providing access to Medicare claims data used in this study. This work was supported by the National Institute on Aging (grant R01AG074357 K.S.) and the National Institute of Environmental Health Sciences (1R01ES034175 Y.L.).

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Author notes

  1. These authors contributed equally: Hua Hao, Yanling Deng.

  2. These authors jointly supervised this work: Hua Hao, Yang Liu, Kyle Steenland.

Authors and Affiliations

  1. Gangarosa Department of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, GA, USA

    Hua Hao, Yanling Deng, Ke Xu, Yang Liu & Kyle Steenland

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  1. Hua Hao
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Contributions

H.H., Y.L. and K.S. designed the research; H.H., Y.D. and K.X. performed the research; H.H., Y.D. and K.X. analyzed the data; and H.H. wrote the paper.

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Correspondence to Hua Hao, Yang Liu or Kyle Steenland.

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Hao, H., Deng, Y., Xu, K. et al. A national cohort study of long-term exposure to PM2.5 trace element components and depression in older adults in the USA. Nat. Mental Health 4, 377–386 (2026). https://doi.org/10.1038/s44220-025-00524-1

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