Cancer mortality in nuclear industry workers in Japan

Since 1990 we have been conducting a cohort study on nuclear industry workers in Japan using the exposure dose record for each worker filed at the Radiation Dose Registration Center (RADREC) and resident record cards transcribed at municipal offices. The causes of death were identified by record linkage with national vital statistics death records. A prospective follow-up during 1991-2002 was successfully made for 200,583 males, and there were 7,670 deaths from all causes and 3,093 deaths from all cancers. The mean cumulative dose of this population was 12.2mSv. The SMR (95% CI) was 1.02 (0.98-1.05) for all cancers, 1.13 (1.04-1.23) for liver cancer and 1.08 (1.00-1.17) for lung cancer. In the trend analyses, while mortality for leukemia excluding CLL did not show a significant increase with cumulative doses (p=0.691), mortality for all cancers excluding leukemia did (p=0.047). There was a positive correlation with doses for esophageal cancer (p=0.002), for liver cancer (p=0.040) and for multiple myeloma (p=0.021). The lifestyle survey separately performed with approximately 45,000 workers from the nested cohort indicated that the habits of heavier smoking and drinking and also the history of occupational exposures to hazardous materials were positively correlated with cumulative doses. With very likely involvement of potentially confounding factors taken into account, this study did not prove that low levels of radiation increased the mortality for cancer.