# Association of shift work with metabolic dysfunction-associated fatty liver disease among subway workers

## TL;DR

This study found that subway workers who do shift work have a higher risk of developing fatty liver disease, especially after working shifts for more than three years.

## Contribution

The study reveals a J-shaped relationship between shift work duration and MAFLD risk, with BMI mediating about half of the association.

## Key findings

- Subway workers with more than 3 years of shift work had a significantly higher risk of MAFLD.
- BMI mediated approximately 40-50% of the association between shift work and MAFLD.
- Three-shift and four-shift systems showed increased MAFLD risk compared to no shift work.

## Abstract

Inconsistent associations between shift work and metabolic dysfunction-associated fatty liver disease (MAFLD) have been suggested. This study aimed to investigate the association between shift work characteristics and MAFLD in subway workers.

This cross-sectional study was conducted in Wuhan, China, between December 2018 and January 2019, with 9,105 subway workers included after excluding participants with missing data on shift work or ultrasonography, with cancer, or with insufficient data to diagnose MAFLD. All participants were on-duty employees, covering various functional positions such as train drivers, station attendants, maintenance technicians, and administrative staff. Information on demographics, occupational history, and lifestyles was collected through standardized questionnaires. We used logistic regression models to estimate the association of shift work duration and types with MAFLD, and restricted cubic spline regression to examine the potential nonlinear relationship. Mediation analyses were employed to evaluate the potential mediating role of body mass index (BMI).

Compared with participants with no shift work, the multivariable-adjusted ORs (95% CIs) for those with ≤3, 3–6, and >6 years of shift work were 0.80 (0.68, 0.94), 1.21 (1.04, 1.41), and 1.60 (1.37, 1.88), respectively. A J-shaped relationship between shift work duration and MAFLD (Poverall < 0.001, Pnonlinear = 0.002) was observed, with the likelihood of MAFLD substantially increased after 3 years of shift work. Compared with participants with no shift work, MAFLD risk increased by 13% (OR:1.13, 95% CI: 0.95, 1.34), 22% (OR: 1.22, 95% CI: 1.05, 1.42), and 21% (OR: 1.21, 95% CI: 1.02, 1.42) for those worked in two-shift, three-shift, and four-shift, respectively. BMI adjustment attenuated these associations, with mediation analyses revealing significant mediation effects: mediation proportion was 48.5% (34.0, 64.0%) for shift work duration, 42.9% (5.0, 99.4%) for three-shift, and 47.5% (4.4, 111.5%) for four-shift systems (all P < 0.05).

Both shift work duration and rotation systems were associated with MAFLD risk in subway workers, with BMI mediating approximately half of these relationships.