Workers' Mental Health, Long Work Hours, and Workplace Management: Evidence from workers' longitudinal data in Japan

Using workers' longitudinal data, this paper investigates the relationship between long work hours and workers' mental health. The number of workers suffering from mental disorders has increased significantly in this decade, and many believe that overwork is the primary reason for deterioration in mental wellness in Japan. Nevertheless, most of the previous studies in social science and epidemiology investigating the effect of work hours on mental health control neither individuals' fixed factors nor detailed information of workers and workplace characteristics. By tracing 700 workers' mental health conditions for two consecutive years along with collecting detailed information related to the workplace, this paper examines whether there are any work-related causes that may damage workers' mental health. Our main findings are summarized as follows. First, assessing workers' mental health by the General Health Questionnaire (GHQ12), we found that workers' mental health changes drastically within a two-year period. Second, even after controlling for workers' fixed effect and other detailed characteristics, we establish that long work hours is one of the principal causes which deteriorate workers' mental health. We also found that unpaid overwork especially worsens workers' mental health. This trend is observed particularly among highly educated male workers under the age of 40. On the other hand, regardless of being paid or unpaid, long work hours tend to damage the mental health of female and low-educated workers. This may imply that time constraint differs among the workers' group. Third, we also found that job characteristics and workplace practices influence workers' mental health significantly. These findings suggest that good workplace practices, including management of work hours, would be influential to improve workers' mental health.