Objectives Accumulated evidence implies that night shift work may trigger liver dysfunction. Non-alcoholic fatty liver (NAFL) is suggested to be a necessary mediator in this process. This study aimed to examine the relationship between night shift work and elevated level of alanine transaminase (e-ALT) of workers and investigate the potential mediation effect of NAFL.
Methods This study included all male workers from the baseline survey of a cohort of night shift workers. Information on demographics, lifestyle and lifetime working schedule was collected by face-to-face interview. Liver sonography was used to identify NAFL cases. Serum ALT level was detected by an automatic biochemical analyser. e-ALT was defined as ALT >40 U/L. Logistic regression models were used to evaluate ORs, and mediation analysis was employed to examine the mediation effect.
Results Among 4740 male workers, 39.5% were night shift workers. Night shift workers had an increased risk of e-ALT (OR, 1.19, 95% CI 1.00 to 1.42). With the increase in night shift years, the OR of e-ALT increased from 1.03 (95% CI 0.77 to 1.36) to 1.60 (95% CI 1.08 to 2.39) among workers without NAFL. A similar trend was not found among workers with NAFL. In addition, no significant mediation effect of NAFL in the association between night shift work and e-ALT was found.
Conclusions Night shift work is positively associated with abnormal liver function, in particular among workers without NAFL. Shift work involving circadian disruption is likely to exert a direct effect on liver dysfunction rather than rely on the mediation effect of NAFL.
- shift work
- liver function
- mediation effect
- non-alcoholic fatty liver
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Contributors FW raised the study concept and drafted the manuscript. LZ, SW, WF, MS and YZ collected the data and performed the statistical analyses. WL, DD, SY-SW, GJE, RCHV and EY-YC critically revised the manuscript. PZ critically reviewed the manuscript and provided imported clinical comments. YKW, JZ and JJV critically reviewed the manuscript and provided important comments, which highly improved the quality of this study. ZL supervised the fieldwork of this project. LAT was in charge of the entire project, including supervision of the fieldwork data collection, and she also revised the manuscript critically.
Funding This work was supported by the National Natural Science Foundation of China (project numbers 81273172 and 81372964).
Competing interests None declared.
Patient consent Obtained.
Ethics approval The protocol was approved by the Joint Chinese University of Hong Kong - New Territories East Cluster Clinical Research Ethics Committee, Hong Kong (CREC Ref No: CRE-2013.107).
Provenance and peer review Not commissioned; externally peer reviewed.
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