2018 年 53 巻 3 号 p. 146-153
Whether exposure to radiation at low dose and at low dose rate is related to leukemia mortality and morbidity remains controversial. Cohort studies of nuclear workers chronically exposed to radiation at low dose and at low dose rate in their workplaces provide an opportunity to directly evaluate the risks of leukemia in the lower dose ranges. Previous findings have come mostly from Western countries, with few from Asian countries. The present study aimed to examine radiation’s effects on mortality from leukemia, in a cohort of Japanese nuclear workers. The cohort consisted of 204,103 workers, who were followed from 1991 to 2010, with a total of 2.89 million person-years. The mean age and mean cumulative dose at the age at the end of follow-up were 55.6 years and 13.8 mSv. During the study, 209 leukemia deaths were observed. The linear excess relative risk (ERR) for all types of leukemia was negative, but not significant (ERR/Sv = -0.54; 90% confidence interval; -4.04, 2.96). Specific types of leukemia also showed no significant risks. A significant radiation-leukemia association for mortality was not observed in this study of Japanese nuclear workers. The cohort, however, is still young. Further follow-up is needed to obtain more reliable estimates of leukemia risks for Japanese workers exposed to low dose and low-dose rate radiation.