Long-term exposure to air pollution, habitual physical activity and risk of non-alcoholic fatty liver disease: A prospective cohort study

Background: Emerging studies suggest a positive association between air pollution exposure and risk of nonalcoholic fatty liver disease (NAFLD), however, the combined effects of long-term exposure to air pollution, physical activity (PA), and risk of NAFLD is unclear.Methods: We included 58,026 Taiwan residents who received a standard medical screening program between 2001 and 2016. Levels of fine particulate matter (PM2.5) at each participant's residential address were estimated using multiple satellite-based aerosol optical depth data combined with a chemical transport model. PA volume was calculated as hours of metabolic equivalent tasks per week (MET-h/week) based on a standard selfadministered questionnaire. Incident NAFLD was defined as the first occurrence of a fatty liver index (FLI) value > 30 or a hepatic steatosis index (HSI) value > 36 in participants without NAFLD at the baseline. Timevarying Cox regression was used to evaluate the combined effects of PA and PM2.5.Results: Exposure to PM2.5 was positively associated with NAFLD. A 1 mu g/m3 increase in PM2.5 above 23.5 mu g/m3 was associated with a hazard ratio (HR) of 1.06 (95% CI: 1.04, 1.09) and 1.05 (95% CI: 1.03, 1.07) for NAFLD identified by FLI and HSI, respectively. Performing PA was inversely associated with NAFLD. Compared with participants in high PM2.5 [> 27.5 mu g/m3]-very low PA [< 3.75 MET-h/week] group, low PM2.5 [< 23.5 mu g/m3]- very high PA [> 25.50 MET-h/week] group had a 57% (95% CI: 50%, 63%) and 42% (95% CI: 33%, 50%) lower risk of NAFLD defined by FLI and HSI, respectively. We found no evidence of any additive or multiplicative interaction between PA and PM2.5.Conclusion: Long-term PM2.5 exposure was positively associated with NAFLD, whereas performing PA was inversely associated with NAFLD. The benefits of PA on NAFLD remained stable in participants exposed to various PM2.5 levels.

Automated summary

Long-term exposure to PM2.5 is positively associated with NAFLD, while engaging in physical activity is inversely associated with NAFLD. The benefits of physical activity on NAFLD remain consistent across various levels of PM2.5 exposure.