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Occupational and environmental medicine
Original research
Cross-sectional association between long working hours and liver function: the Kangbuk Samsung Health Study
  1. Eunchan Mun1,
  2. Woncheol Lee1,
  3. Min-Woo Nam1,
  4. Hyun-Il Kim1,
  5. Hyeongcheol Kim1,
  6. Yesung Lee1,
  7. Soyoung Park1,2
  1. 1Department of Occupational and Environmental Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea
  2. 2Total Healthcare Center, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea
  1. Correspondence to Dr Soyoung Park; syoem.park{at}gmail.com

Abstract

Objectives Although the effects of long working hours on liver function remain unclear, in South Korea, there is a social perception that long working hours are associated with poor liver function. Thus, long working hours have recently become a major issue. This study aimed to determine the association between long working hours and liver function, as indicated by the alanine transaminase (ALT) levels.

Design Cross-sectional study.

Setting Large university hospitals in Seoul and Suwon, South Korea.

Participants Workers in formal employment who underwent a comprehensive health examination at the Kangbuk Samsung Hospital Total Healthcare Centre clinics in Seoul and Suwon, South Korea, between January 2011 and December 2018. Of the 386 488 participants, 212 421 met the inclusion criteria and were included in the analysis.

Primary outcome measure ALT elevation.

Results The participants were predominantly well-educated (86.1%), male (69.3%) and in their 30s (49.6%). In total, 13.4% of the participants presented ALT elevation (>40 IU/L). There was no significant association between working hours and ALT elevation in the general population and in the hepatitis B surface antigen (HBsAg)-negative group. Conversely, in the HBsAg-positive group, working >60 hours per week compared with 35–40 hours per week was significantly associated with ALT elevation. The association was more pronounced in those with ALT levels >80 IU/L (OR 1.94, 95% CI 1.24 to 3.01) than in those with ALT levels >40 IU/L (OR: 1.45, 95% CI 1.20 to 1.75). The p values for trend were <0.05.

Conclusions Long working hours were associated with ALT elevation only in hepatitis B virus carriers and not in the general population. Provided that there is adherence to the legal working hours, there is no need to further restrict working hours for liver health, irrespective of HBsAg status.

  • occupational & industrial medicine
  • public health
  • hepatology
http://creativecommons.org/licenses/by-nc/4.0/

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

https://doi.org/10.1136/bmjopen-2020-041595

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    Footnotes

    • Contributors EM, WL and SP contributed to the conception and design of the study. EM, M-WN, H-IK, HK, YL and SP participated in the data collection and have made substantial contributions to the statistical analysis and interpretation of the data. EM and SP prepared the first draft of the manuscript. WL and SP have made substantial contributions to revising the manuscript critically for important intellectual content. All authors have approved the final version submitted for publication.

    • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

    • Competing interests None declared.

    • Patient consent for publication Not required.

    • Ethics approval The study was approved by the Institutional Review Board of Kangbuk Samsung Hospital (approval number: KBSMC 2020-02-049).

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data availability statement Data are available on reasonable request. The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.