Background: Lung cancer incidence among never-smoking women in Xuanwei, China, ranks among the highest worldwide and is largely attributed to household air pollution (HAP) from smoky (bituminous) coal combustion, with early-life exposures possibly playing a critical role. We conducted an epigenome-wide DNA methylation (DNAm) analysis across multiple exposure windows to elucidate molecular mechanisms. Methods: Leukocyte DNAm was measured in 106 never-smoking women (23 with repeated measurements). Fuel use was obtained through questionnaires, and extensive personal and environmental monitoring was conducted. Validated exposure models estimated 43 HAP constituents, primarily polycyclic aromatic hydrocarbons (PAHs), across childhood, current, and cumulative exposure windows. Hierarchical clustering derived exposure clusters. We used generalized estimating equations to identify CpG sites associated with HAP exposure and PAH clusters, including 5-methylchrysene, a methylated PAH previously linked to lung cancer. Results: We identified several differentially methylated CpG sites, predominantly hypomethylated with HAP exposure. Although some DNAm signatures overlapping with smoking (cg05575921; AHRR) were observed, most changes were distinct. A life-course assessment indicated persistent epigenetic variations across childhood and cumulative exposures, suggesting that early-life exposures may have lasting effects at certain sites (SLC43A2). Within the PAH clusters, 5-methylchrysene appears to be a significant contributor to DNAm variations. Top CpG sites were linked to immune regulation, cell growth and proliferation, and molecular mechanisms of cancer, including lung cancer. Conclusions: Our findings provide novel insights into HAP-induced DNAm changes and their potential health effects. Future studies with larger sample sizes, and diverse coal use settings are needed to validate and extend these findings.

The authors have declared no competing interest.

This project was supported by the National Institutes of Health (HHSN261201400122P) intramural research program. The content of this publication does not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.

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