[Estimate of the number of night shift workers in Japan].

In this study we used governmental statistic data to estimate the number of night shift workers in Japan, referring to the Labour Force Survey by the Ministry of Internal Affairs and Communications to obtain the number of employees in the workforce. We also referred to the Survey on the State of Employees' Health by the Ministry of Health, Labour and Welfare to obtain the work schedules of employees. Our study revealed that the number of night shift workers in Japan has been increasing. The prevalence of night work among Japanese employees was 13.3% in the year 1997, 17.8% in 2002, 17.9% in 2007, and 21.8% in 2012. Our estimation revealed that there are twelve million workers currently engaged in night work. The prevalance of shift workers and shift workers with night shift in Japan is also increasing.