Correlation between natural radiation exposure and cancer mortality (5).

In the previous study, a statistically significant positive correlation between natural background radiation exposure rates and crude (non-age-adjusted) cancer mortality rates was observed in 46 Japanese prefectures over the period from 1968 until 1978. However, the significance of this correlation mostly disappeared through age adjustment. It was suggested that natural radiation levels are positively correlated with population component ratios older than 40, 50 and 65 years, which was considered to be one of the causes of the apparent correlation between exposure rates and crude cancer mortality rates. In order to confirm these facts, we also examined the correlation between natural background radiation exposure rates and cancer mortality rates over two other periods: 1950-1957 and 1958-1967. Furthermore, we carried out a long-term analysis for the period 1950-1978, including the data of the previous report. In all periods, statistically significant positive correlation coefficients were observed in most cases of cancer with only a few exceptions. However, as in the previous study, the significance of the correlation mostly disappeared through age-adjustment with only one exception of uterine cancer in 1958-1978. 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 with the developing use of nuclear energy. Also, studies on the statistical significance of the correlation between cancer mortality rate and natural background exposure rate have been becoming important as basic data on the effects of artificial ionizing radiation. 清 水 雅 美*,野 口 邦 和*,西 連 寺 永 康*,**: Radioisotope Research Laboratory* and Department of Radiolog**, Nihon Uniyersity Seheol of Dentistry. 安 斉 育 郎***: Faculty of Economics, Ritsumeikan University.