Shift work and evening chronotype are associated with hepatic fat fraction and non-alcoholic fatty liver disease in 282,303 UK biobank participants.

Background and aims: Non-alcoholic fatty liver disease (NAFLD) has rapidly become the most common liver disease worldwide. Modern lifestyles have been linked to this rise in prevalence with changes in rhythmic human behaviour emerging as a possible mechanism. We investigated how shift working patterns and chronotype were associated with hepatic fat fraction and NAFLD in 282,303 UK Biobank participants. Methods: We stratified participants into day, irregular-shift, and permanent night-shift workers. We then utilised multiple methods of disease identification including (i) Dallas steatosis index (DSI), (ii) ICD10 codes, and (iii) hepatic proton density fat fraction (PDFF) and examined how shift work exposure impacted these variables. We further assessed the relationship of baseline chronotype with liver phenotypes using these same outcome measures. Results: Compared to day workers, irregular-shift workers were more likely to have a high DSI (OR 1.29 (1.2-1.4)) after adjusting for major covariates with some attenuation after additional adjustment for BMI (OR 1.12 (1.03-1.22)). Likelihood of high DSI was also increased in permanent night-shift workers (OR 1.08 (0.9-1.29)) in the fully adjusted model. Mediator analysis revealed that BMI was a significant mediator of the shift work effect. Compared to participants with intermediate chronotype, those with extreme late chronotype had a higher likelihood of high DSI defined NAFLD (OR 1.45 (1.34-1.56)) and a higher likelihood of NAFLD/NASH by ICD10 code (OR 1.23 (1.09-1.39)). Hepatic PDFF was elevated in irregular shift workers, but not permanent night-shift workers. Conclusions: Irregular-shift work and extreme late chronotype are associated with pathological liver fat accumulation, suggesting circadian misalignment may have an underlying pathogenic role. These findings have implications for health interventions to mitigate the detrimental effect of shift work.