Association between working evening shifts and mental health among Korean employees: data from the 5th Korean Working Conditions Survey.

Background: Many studies have been conducted to investigate the harmful effect of shift work on physical and mental health. Although, by definition, "working evening shift" is included in the scope of shift work, most related studies conducted thus far have focused on working night shifts, overtime work, or different types of shift work, with little research effort dedicated to "working evening shifts." Therefore, to fill this research gap, we investigated the effect of working evening shifts on workers' mental health.

Methods: The participants of this study were 16,692 employees of the 50,205 that participated in the 5 wave of the Korean Working Conditions Survey. We performed χ test and logistic regression analysis to analyze the effects of independent variables on health problems and calculated odds ratios and 95% confidence intervals (CIs).

Results: In the logistic regression analysis adjusted for sociodemographic characteristics, health-related factors, and work-related characteristics, employees who worked evening shifts showed higher levels of depression and anxiety compared to those that did not. In particular, the adjusted odds ratios of the group working evening shifts between one and nine times a month were the highest with 2.723 (95% CI: 2.014-3.682) for depression, 3.294 (95% CI: 2.547-4.259) for anxiety.

Conclusions: The results of our study suggest that working evening shifts has a negative effect on employees' mental health. This trend decreased with an increase in the monthly frequency of evening work.