Studies of the mortality of atomic bomb survivors. Report 12, part II. Noncancer mortality: 1950-1990

This report updates the data on noncancer mortality for 86,572 atomic bomb survivors with dose estimates in the Radiation Effects Research Foundation' s Life Span Study cohort. The primary analyses are based on more than 27,00 0 noncancer disease deaths that occurred in the cohort between October 1, 1 950, and December 31, 1990, 30% more than in the previous report. The prese nt analyses strengthen earlier findings of a statistically significant incr ease in noncancer disease death rates with radiation dose. Increasing trend s are observed for diseases of the circulatory, digestive and respiratory s ystems. Rates for those exposed to 1 Sv are elevated about 10%, a relative increase that is considerably smaller than that for cancer. However, estima tes of the number of radiation-related noncancer deaths in the cohort to da te (140 to 280) are 50 to 100% of the number for solid cancer. The data do not yet clarify the shape of the dose response. There is no significant evi dence against linearity, but the data are statistically consistent with cur vilinear dose-response functions that posit essentially zero risk for doses below 0.5 Sv. Similarly, while the data are consistent with substantial va riation in the excess relative risk with age at exposure or attained age, t here is no statistically significant dependence on these factors. In view o f the small relative risks and the lack of understanding of biological mech anisms, we emphasize consideration of whether the findings could be explain ed by misclassification, confounding or selection effects. Based on availab le data, we conclude that such factors are unlikely to fully explain the ob served dose response. A significant dose response is also seen for deaths f rom blood diseases with an excess relative risk that is several times great er than that seen for solid cancer. Particular attention is paid to the pos sibility that this apparent effect is a consequence of the attribution of l eukemia or other cancer deaths to noncancer blood diseases. We find that mi sclassification does not explain this excess risk. As in earlier reports, s uicide rates tend to decrease with increasing dose. (C) 1999 by Radiation R esearch Society.