Association between long working hours and liver enzymes: evidence from the Korea National Health and Nutrition Examination Survey, 2007-2017

Background: Long working hours causes several health risks, but little is known about its effects on the liver. This study aimed to examine the correlation between working hours and abnormal liver enzyme levels. Methods: We used data from the Korea National Health and Nutrition Examination Survey IV-VII. For the final 15,316 study participant, the information on working hours was obtained through questionnaires, and liver enzyme levels, consisting of serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), through blood tests. The relationship between weekly working hours and abnormal levels of liver enzymes was analyzed using multiple logistic regression, and a trend test was also conducted. Results: In male, working ≥ 61 hours per week was significantly associated with elevated AST and ALT levels compared with working 35-52 hours per week. Even after adjusting for covariates, the odds ratios (ORs) of abnormal AST and ALT increased by 1.51 (95% confidence interval: 1.20-2.05) and 1.25 (1.03-1.52), respectively, and a dose-response relationship was observed. This association was more prominent among the high-risk group, such as those aged > 40 years, obese individuals, worker on non-standard work schedule, pink-collar workers, or temporary worker. No correlation was observed in female. Conclusions: Long working hours are associated with abnormal liver function test results in male. Strict adherence to statutory working hours is necessary to protect workers' liver health.