The Impact of Long Working Hours on Mental Health Status in Japan: Evidence from a National Representative Survey

Using the long-term Comprehensive Survey of Living Conditions (CSLC), a nationally representative survey conducted in Japan from 2003 to 2019, we examine the impact of long working hours on mental health in Japan while addressing the endogeneity issue arising from non-random selection bias. Additionally, we assess variations in the effect of long working hours on mental health across different groups. This study yields three primary conclusions. First, individuals working longer hours (55 hours or more per week) exhibit a higher likelihood of developing mental illness compared to those working regular or fewer hours. Second, the negative effect of long working hours on mental health is more pronounced among non-regular workers than among regular worker groups. These conclusions are corroborated by results obtained through the propensity score matching method. Third, the effect of long work hours on mental health varies among different demographic groups, with greater impact observed among women, managers, non-regular workers, employees in small or large-sized firms, and those in smaller cities compared to their counterparts. The results suggest that, in order to enhance worker productivity, the Japanese government should address the issue of long working hours to improve the mental well-being of employees. Initiatives aimed at promoting work-life balance, family-friendly policies, and measures to ameliorate working conditions, such as reducing the wage gap between non-regular and regular workers, are expected to help mitigate the challenges associated with long working hours and mental health issues, especially among non-regular workers.