Exposure to air pollution and risk of gastrointestinal diseases: A systematic review and meta-analysis of epidemiological evidence

Gastrointestinal (GI) diseases represent a significant global health burden, and emerging evidence suggests that air pollution may be a risk factor. We aimed to review the epidemiological literature on air pollution and GI diseases and perform a meta-analysis. We searched original studies published as of September 20, 2024, which investigated the associations between long- and short-term exposure to particulate matter [diameter ≤ 2.5 mm (PM2.5), ≤ 10 mm (PM10)] and gaseous pollutants [nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), and ozone (O3)] and GI diseases. DerSimonian and Laird random-effects meta-analyses were conducted when at least two studies were available for a given pollutant (per 10 μg/m3 increment) and a specific GI disease. A total of 70 studies were included. Long-term exposure to PM2.5 was significantly associated with an increased mortality from all GI cancers [OR = 1.128; 95% confidence interval (CI): 1.019, 1.248], with the strongest association observed for colorectal cancer (1.214; 1.061, 1.389). For non-cancer GI diseases, long-term exposure to PM2.5 was significantly associated with increased risks of duodenal ulcer (1.073; 1.057, 1.089) and irritable bowel syndrome (1.353; 1.222, 1.497), while PM10 was also linked to the latter (1.108; 1.012, 1.213). Meanwhile, short-term exposure, particularly PM2.5, PM10, and O3 was significantly associated with appendicitis hospitalization [(1.003; 1.001, 1.004), (1.017; 1.015, 1.019), and (1.001; 1.000, 1.003), respectively]. PM2.5 was also associated with peptic ulcer bleeding (1.006; 1.001, 1.011). Both long- and short-term exposure to air pollution, especially PM2.5, is associated with increased risks of GI diseases.