The Hidden Connection Between Air Quality and Gut Health

Multiple air pollutants can increase the risk of gastrointestinal (GI) diseases after long-term exposure, emphasizing the need for more public health measures to reduce air pollution, according to a study published in BMC Public Health.1

Over 99% of the global population lives in areas exceeding WHO air quality guidelines, with ambient air pollution responsible for 4.2 million deaths each year. | Image credit: Margarita - stock.adobe.com

This study was conducted to address the limited understanding of how long-term exposure to air pollution affects GI health. While previous research has established strong links between air pollutants and various respiratory, cardiovascular, neurological, and metabolic diseases, their impact on the GI system remains underexplored.

Emerging evidence suggests that air pollutants, especially particulate matter (PM2.5 and PM10), sulfur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), and carbon monoxide (CO), may harm the GI tract by triggering inflammation, disrupting gut microbiota, and increasing intestinal permeability, potentially contributing to conditions like inflammatory bowel disease and GI cancers. Building on earlier findings from a cross-sectional study, the present study used data from the nationally representative China Health and Retirement Longitudinal Study (CHARLS) to investigate the long-term effects of air pollution on GI disease risk.

According to the World Health Organization (WHO), approximately 2.4 billion people use polluting fuels for cooking and heating, leading to 3.2 million premature deaths annually from household air pollution.2 Additionally, over 99% of the global population lives in areas exceeding WHO air quality guidelines, with ambient air pollution responsible for 4.2 million deaths each year.

NO2 comes from fuel combustion and worsens respiratory issues.2 It also helps form O3, which forms in sunlight from volatile organic compounds, nitric oxides, and CO, and it is known to affect lung function and asthma. CO from incomplete combustion blocks oxygen delivery, causing fatigue, and can be fatal. SO2 from burning fossil fuels can trigger asthma and may require hospital visits if inhaled in large amounts.

The CHARLS was a nationally representative cohort that began in 2011 and included follow-ups in 2013, 2015, 2018, and 2020.1 This longitudinal design allowed for the assessment of evolving exposure to multiple air pollutants and their association with the development of GI diseases over time. The study also evaluated the influence of demographic and behavioral factors on the relationship, such as age, sex, smoking, alcohol consumption, and urban vs rural residence.

The study found that average concentrations of major air pollutants were: PM2.5 at 49.13 µg/m3, PM10 at 84.47 µg/m3, SO2 at 22.36 µg/m3, NO2 at 28.28 µg/m3, O3 at 90.17 µg/m3, and CO at 1.01 mg/m3. Strong positive correlations were observed among PM2.5, PM10, SO2, NO2, and CO (range, 0.71 to 0.92), whereas O3 showed weaker correlations, particularly with CO (0.43) and SO2 (0.50).

Long-term exposure to PM2.5, PM10, SO2, NO2, and CO was consistently associated with an increased incidence of GI disease, while O3 was associated with a decreased risk. In fully adjusted models, HRs for GI disease per IQR increase were: PM2.5 (HR, 1.38), PM10 (HR, 1.31), SO2 (HR, 1.74), NO2 (HR, 1.21), CO (HR, 1.48), and O3 (HR, 0.56).

Subgroup analyses revealed stronger pollutant-disease associations among urban residents, drinkers, and individuals in poor health, with regional variations indicating the highest risks in the Northeast for PM2.5 and PM10, the Western region for SO2 and NO2, and the Central region for CO.

Conversely, O3’s protective effect was strongest in Western China, particularly among urban residents and nonsmokers. Sensitivity analyses, including propensity score matching and exclusion of participants in poor health, confirmed the robustness of these findings, emphasizing the need for targeted air quality interventions to mitigate health risks.

Limitations included the potential influence of unmeasured confounders like diet and occupation, as well as reliance on residential addresses to estimate individual exposure levels. Overall, the research highlights a clear link between air pollution and GI diseases and underscores the importance of targeted public health strategies to address environmental and behavioral risk factors.

The authors concluded, “Based on these findings, we recommend that public health policies focus on reducing the concentration of air pollutants, especially in urban areas, and adopt targeted interventions for high-risk populations to mitigate the health burden posed by air pollution.”

References

1. Kou Ym Ye S, Du W, et al. Long-term exposure to air pollution and gastrointestinal disease: findings from a nationwide cohort study in China. BMC Public Health. 2025;25(1):1011. doi:10.1186/s12889-025-21910-5

2. Air pollution is responsible for 6.7 million premature deaths every year. WHO. Accessed April 21, 2025. https://www.who.int/teams/environment-climate-change-and-health/air-quality-and-health/health-impacts/types-of-pollutants