Association of nitrogen dioxide with non-alcoholic fatty liver disease in Chinese rural older adults: The mediating role of fasting plasma glucose.

BACKGROUND

Evidence for the association between nitrogen dioxide (NO2) exposure and non-alcoholic fatty liver disease (NAFLD) in older adults remains limited, and the underlying mechanisms are not well understood. This study aimed to investigate the relationship between long-term NO2 exposure and NAFLD and to assess the potential mediating role of fasting plasma glucose (FPG) in a Chinese elderly population.

METHODS

We analyzed baseline data from 3662 participants in an ongoing longitudinal aging cohort. Annual average NO2 concentrations were estimated using a Space-Time Extra-Trees model incorporating satellite-based and land-use variables. NAFLD was diagnosed using standardized abdominal ultrasonography. Logistic regression and restricted cubic splines (RCS) were employed to evaluate the exposure-response relationship, and causal mediation analysis was conducted to explore whether FPG lies on a pathway linking long-term NO2 exposure with NAFLD, with adjustment for key covariates.

RESULTS

Each interquartile range (IQR) increase (0.30 μg/m3) in the 4-year average NO2 concentration was associated with a 27.8 % increase in the odds of NAFLD (OR = 1.278, 95 % CI: 1.132-1.444). A linear dose-response relationship was confirmed by RCS. Mediation analysis indicated that FPG accounted for 3.84 % (95 % CI: 0.28 %-11.19 %) of the total association between NO2 exposure and NAFLD.

CONCLUSIONS

Long-term NO2 exposure is positively associated with NAFLD prevalence among older adults in China, and FPG partially mediates this association. These findings highlight ambient NO2 pollution as a potentially modifiable environmental risk factor for NAFLD and underscore the need for further validation in large-scale prospective studies.