Ambient Air Pollution and Digestive Diseases: Epidemiological Evidence, Biological Mechanisms, and Research Priorities

Abstract

Ambient air pollution is increasingly recognized as a potentially modifiable determinant of digestive health. Evidence spans particulate matter (PM2.5 and PM10), nitrogen dioxide, nitrogen oxides, sulfur dioxide, ozone, carbon monoxide, black carbon, traffic-related pollution, and specific particulate constituents. Epidemiological research has expanded from acute gastrointestinal events to functional disorders, inflammatory bowel disease, metabolic dysfunction-associated steatotic liver disease (MASLD), cirrhosis, gallstone disease, and digestive system cancers. The strongest and most consistent evidence concerns chronic liver injury and steatotic liver disease, with prospective cohorts and meta-analyses linking long-term PM2.5 and nitrogen oxides to abnormal liver enzymes, MASLD, fibrosis, and cirrhosis. Emerging evidence also supports associations with irritable bowel syndrome, peptic ulcer disease, gastroesophageal reflux disease, appendicitis, and ulcerative colitis, although heterogeneity remains substantial. For cancer, colorectal and liver cancer currently show the most consistent associations, whereas findings for gastric, esophageal, and pancreatic cancers are less stable across populations. Plausible mechanisms include swallowed particle deposition, oxidative stress, epithelial barrier disruption, gut microbial dysbiosis, altered microbial metabolites, systemic inflammation, mitochondrial dysfunction, and genotoxic or epigenetic effects. Major limitations include exposure misclassification, residual confounding by diet and lifestyle, single-pollutant modeling, inconsistent disease definitions, and limited repeated exposure and biomarker data. Future research should prioritize prospective multi-exposure designs, source-specific particulate analyses, microbiome and multi-omics integration, and stronger causal inference. Overall, air pollution should be considered an important environmental determinant of digestive health, with risk varying by organ, pollutant, exposure window, and host susceptibility.

Keywords: Air Pollution; Particulate Matter; Gastrointestinal Disease; MASLD; Gut Microbiota; Colorectal Cancer; Liver Disease; Digestive Health