Non-linear association between long-term air pollution exposure and risk of metabolic dysfunction-associated steatotic liver disease

Background: Metabolic Dysfunction -associated Steatotic Liver Disease (MASLD) has become a global epidemic, and air pollution has been identified as a potential risk factor. This study aims to investigate the non-linear relationship between ambient air pollution and MASLD prevalence. Method: In this cross-sectional study, participants undergoing health checkups were assessed for three-year average air pollution exposure. MASLD diagnosis required hepatic steatosis with at least 1 out of 5 cardiometabolic criteria. A stepwise approach combining data visualization and regression modeling was used to determine the most appropriate link function between each of the six air pollutants and MASLD. A covariate-adjusted six -pollutant model was constructed accordingly. Results: A total of 131,592 participants were included, with 40.6% met the criteria of MASLD. "Threshold link function," "interaction link function," and "restricted cubic spline (RCS) link functions" best -fitted associations between MASLD and PM2.5, PM10/CO, and O3 /SO2/NO2, respectively. In the six -pollutant model, significant positive associations were observed when pollutant concentrations were over: 34.64 mu g/m3 for PM2.5, 57.93 mu g/m3 for PM10, 56 mu g/m3 for O3, below 643.6 mu g/m3 for CO, and within 33 and 48 mu g/m3 for NO2. The six -pollutant model using these best -fitted link functions demonstrated superior model fitting compared to exposurecategorized model or linear link function model assuming proportionality of odds. Conclusion: Non-linear associations were found between air pollutants and MASLD prevalence. PM2.5, PM10, O3, CO, and NO2 exhibited positive associations with MASLD in specific concentration ranges, highlighting the need to consider non-linear relationships in assessing the impact of air pollution on MASLD.