Long-term exposure to ambient air pollution and the incidence of nonalcoholic fatty liver disease: a cohort study

Background Nonalcoholic fatty liver disease (NAFLD) affects approximately one-third of adults and may progress to advanced fibrosis and hepatocellular carcinoma. Epidemiologic studies linking air pollution to NAFLD incidence remain limited. This study examined associations between long-term exposure to ambient air pollution and NAFLD incidence.Methods The study included 62 660 adults in Taiwan undergoing health examinations from 1996 to 2016. NAFLD was diagnosed through liver ultrasonography; individual characteristics and medical history were obtained from questionnaires. Residential township data estimated exposure to fine particulate matter (PM2.5), nitrogen dioxide (NO2), and carbon monoxide (CO). Time-dependent Cox regression was conducted to assess associations between air pollution and NAFLD incidence.Results The overall NAFLD incidence was 53.0 cases per 1000 person-years. Adjusted models showed positive associations between air pollutants and NAFLD. Compared with low exposure to both PM2.5 and NO2, the adjusted hazard ratio (HR) [95% confidence interval (CI)] for high exposure to both was 1.25 (1.19-1.31). Similarly, compared with low exposure to both PM2.5 and CO, the adjusted HR (95% CI) was 1.12 (1.07-1.17) for low PM2.5 and high CO, and 1.28 (1.22-1.33) for high exposure to both.Conclusion Long-term exposure to PM2.5 and traffic-related air pollutants, including NO2 and CO, may increase the risk of developing NAFLD.