Abstract
A cohort study on nuclear industry workers in Japan was initiated in 1990 to determine the health effects of low dose/ low dose-rate radiation with gamma- and X-rays. Among 176,000 male workers constituting the cohort of the second analysis with the observation period from 1991 to 1997, approximately 120,000 workers with prospective follow-up (average of 4.5 years) were subjected to statistical analyses. The standardized mortality ratio (and its 95% confidence interval) was 0.94 (0.90, 0.97) for 2,934 cases of all causes, 0.86 (0.82, 0.91) for 1,305 cases of non-neoplastic diseases and 0.98 (0.93, 1.04) for 1,191 cases of all cancers (External comparisons). In tests for trend of death rate with increasing radiation dose, no significant correlation was found for all cancers combined when the latest place of residence of workers as a potential confounder was adjusted for (Internal comparisons). For site-specific cancers, most cancers including leukemia showed no positive correlation with accumulated dose, except for cancers of the esophagus and some digestive tracts. A separate questionnaire study indicated that these positive results could be ascribed in part to lifestyle characteristics of workers including smoking. With the limited statistical power and the possible involvement of confounding factors, this cohort study has not yielded any definite evidence as to whether low-level radiation elevates cancer mortality.
