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

Abstract

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.

Keywords: air pollution; nonalcoholic fatty liver disease; particulate matter; traffic-related air pollutant.

Figure 1.

Associations between ambient air pollution and the incidence of NAFLD, stratified by smoking status, sleep duration, exercise, and fried-food consumption. Adjusted HRs and 95% CIs are shown. (a) PM_2.5: HRs per IQR increase of 7.4 μg/m³. (b) NO₂: HRs per IQR increase of 8.5 ppb. (c) CO: HRs per IQR increase of 0.27 ppm. HRs and 95% CIs were estimated by using time-dependent Cox regression models adjusted for age, sex, BMI, marital status, educational level, smoking status, sleep duration, exercise, fried-food consumption, and baseline metabolic indicators (e.g. abdominal obesity, hypertriglyceridemia, low high-density lipoprotein cholesterol level, high low-density lipoprotein cholesterol level, hypertension, and elevated fasting blood glucose level). P for interaction represented the likelihood ratio test for interaction between PM_2.5, NO₂, CO, sex, smoking status, sleep duration, exercise, and fried-food consumption. *P < 0.01; **P < 0.001; ***P < 0.0001. Comparisons with P > 0.05 are not shown.