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

Overwork is widely acknowledged as the main culprit behind mental health issues, but research in social science and epidemiology seldomly considers an adequate range of factors when investigating that connection. Using longitudinal data of Japanese workers over four consecutive years, this study investigates how the number of hours worked, job characteristics, and workplace circumstances affect workers' mental health. Using widely used scores in epidemiology to measure the degrees of mental health (General Health Questionnaire), our main findings are as follows. First, long work hours contribute significantly to deteriorations in respondents' mental health, even after controlling for individual fixed effects and other characteristics. Second, the relationship between work hours and mental health is not linear. Working more than 50 hours per week notably erodes the mental health of workers. Third, clear job descriptions, ability to exercise discretion in performing tasks, and workplace atmosphere significantly influence respondents' mental health after controlling for hours worked. Fourth, if a coworker is suffering from mental illness at the workplace, the mental health of other workers are also likely to be poor. These findings suggest that proper workplace practices, including management of work hours, would affirmatively improve workers' mental health.