The Adjustment Effects of Confounding Factors on Radiation Risk Estimates: Findings from A Japanese Epidemiological Study on Low-Dose Radiation Effects (J-EPISODE)

Abstract

Purpose: To investigate the degree of any decreasing effects for excess relative risk (ERR) of radiation exposure caused by adjusting for smoking and years of education. Methods: In this cohort study, we assembled a cohort of 41,742 males who responded to a lifestyle questionnaire survey performed in 2003, were registered in the Radiation Dose Registry as Japanese nuclear workers by the end of March 1999. There were a total of 215,000 person-years, while the number of deaths for all cancers excluding leukemia was 978. Poisson regression was used to quantify ERR per Sv and a comparison of ERRs was performed before adjustment for smoking or years of education and after those adjustments. Findings: For all cancers excluding leukemia, the ERR/Sv was 0.78 (90%CI: -0.65, 2.20). However, it decreased to 0.31 (-1.03, 1.65) when adjusted for smoking and to 0.42 (-0.94, 1.79) when adjusted for years of education. When adjusting for both smoking and years of education, it decreased to 0.08 (-1.22, 1.39). Conclusion: Our results demonstrate the importance of collecting lifestyle data and adjusting for them when estimating radiation risk.