Shift work and metabolic dysfunction-associated steatotic liver disease: a systematic review of observational studies

Abstract Objective Shift work disrupts the circadian rhythm and may increase the risk of metabolic disorders, including nonalcoholic fatty liver disease, recently redefined as metabolic dysfunction-associated steatotic liver disease (MASLD), and its progressive form, metabolic dysfunction-associated steatohepatitis. This systematic review aimed to synthesize observational studies on the association between shift work and MASLD. Methods A comprehensive literature search was conducted in the PubMed, Scopus, and Web of Science databases up to November 25, 2024, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Data were extracted and summarized based on pre-specified inclusion and exclusion criteria. The National Institutes of Health quality assessment tool was used to evaluate the quality of the included studies. Both data extraction and quality assessment were conducted independently by two authors, with disagreements resolved through consensus. Results Nine studies met the criteria and were included in the review, including various occupational groups. Most studies reported a positive association between shift work and MASLD, with stronger effects observed in workers exposed to long-term or frequent shift work. Subgroup and interaction analyses suggested that gender, age, lifestyle, chronotype, and occupational factors may modify this association, while body mass index was identified as a potential mediator of the relationship between shift work and MASLD. However, methodological issues, such as imprecise exposure and outcome measurements and a lack of time-varying analysis, limit causal interpretation. Conclusion The systematic review supports an association between shift work and increased MASLD risk. Further prospective studies with rigorous designs and diverse populations, as well as stronger mechanistic evidence, are needed to establish a causal link between shift work and MASLD.