Background: South Korea is one of the countries with the longest working hours in the OECD countries. The aim of this study was to evaluate the effect of working hours on depressive symptoms and the role of job stress factors between the two variables among employees in South Korea.
Methods: This study used data from the Korea Working Conditions Survey in 2014. Study subjects included 23,197 employees aged 19 years or older who work more than 35 h per week. Working hours were categorized into 35– 39, 40, 41–52, 53–68, and more than 68 h per week. Depressive symptoms were assessed using the WHO’s WellBeing Index with a cut-off score of 13. We calculated prevalence ratios of depressive symptoms according to working hours using log-binomial regression. Through the percentage change in prevalence ratios, we identified the extent of the role of job stress factors that explain depressive symptoms.
Results: The risks of depressive symptoms were significantly higher in people who worked 35–39 h per week (PR: 1.09, CI: 1.01–1.18), 53–68 h/week (PR: 1.21, CI: 1.16–1.25), and more than 68 h/week (PR: 1.14, CI: 1.07–1.21) than 40 h/week, after adjusting for confounding variables. Job stress explained the effects of long working hours on depressive symptoms in about 20–40% of the groups working more than 40 h/week. Among the factors of job stress, social support was 10–30%, which showed the highest explanatory power in all working hours. Reward explained 15–30% in the more than 52 h working group, and reward was the most important factor in the working group that exceeded 68 h.
Conclusions: We showed the working hours could be an independent risk factor for depressive symptoms in employees. To improve workers’ mental health, it is important to strengthen social support in the workplace, to provide adequate rewards as they work, and ultimately to regulate the appropriate amount of working hours.
It is necessary to ensure adequate working hours for the mental health of workers. In the outline of long working hours affecting depressive symptoms, social support and inadequate reward were important factors affecting amount of job stress. Social support was the main explanatory factor of job stress related to working hours and depressive symptom. Therefore, we can infer that the social support of managers and colleagues in the workplace can play an important role in relieving depressive symptoms. It can help the mental health of workers through the managers’ leadership, respect of personalities, dispute resolution, organizational skills, and colleagues’ cooperation and support. In workers who work more than 68 h, reward accounted for a considerable portion of depressive symptom. When there was inadequate reward for hours worked, it was a risk factor for depressive symptoms. Therefore, for the mental health of employees, it is necessary to strengthen social support or give appropriate reward according to working hours, and ultimately to work in the suitable hours.