Correlation between Natural Radiation Expousre and Cancer

In the previous studies, correlation between natural background radiation exposure rates and cancer mortality rates in 46 Japanese prefectures was statistically studied over the period of 1950-1978. With regard to the correlation between natural background radiation exposure rate and crude (non-age-adjusted) cancer mortality rate, statistically significant positive correlation coefficients were observed in most cases of cancers with only a few exceptions. However, the significance of the correlation mostly disappeared through age-adjustment with only three exceptions. We examined the cause of this apparent correlation and found that natural radiation levels are positively correlated with prefectural population component ratios for those inhabitants older than 40, 50 and 65 years. The atomic bombings of Hiroshima and Nagasaki could have affected the cancer mortality in these prefectures and it is reasonable to question the validity of statistical analyses by including these areas together with other prefectures. Therefore, in the present investigation, we carried out recalculations while excluding the data for Hiroshima and Nagasaki prefectures. In most cases of cancers, the correlation did not show any change. However, in the case of female pancreas cancer in 1968-1978, the significance level of negative correlatilon changed from 5% to 10%, and total female cancers and liver cancer for both sexes in 1968-1978 came to show a significant positive correlation at the 10% level. Introduction Ionizing radiation can cause stochastic effects with a probability depending on the dose received, and non-stochastic effects in the dose region higher than the threshold level. Carcinogenesis and genetic effects have been considered to be typical examples of the former. In Japan and elsewhere, there has been a growing interest in the stochastic effects of ionizing radiation following the development of 清 水 雅 美*,野 口邦 和*,西 連 寺 永 康*,**,安 斎 育 郎***:Radioisotope Research Laboratory* and Department of Radiology**, Nihon University School of Dentsitry, 1-8-13, Kanda-Surugadai, Chiyodaku, Tokyo 101, and Faculty of Economics ,Ritsnmeikan University***, Kyoto 603, Japan.