Revision 1
March 19, 1998
by Radiation, Science, and Health, Inc.,
Edited by J. Muckerheide

1.2.1.5
Longevity

"A total of 7782 deaths that occurred during 1970-76 among the bomb survivors registered in Nagasaki City were analyzed as seen in Table 3.1."

Figure 2.7

"The age-specific rates of death from all causes (observed deaths) in people over 60 years of age were significantly lower than those for people without the health handbook (expected deaths) presumed to be unexposed (see also Fig. 2.7). The age-specific death rates for all malignant cancers were, however, not significantly different between the two groups (probably because of the small size of the samples) (Mine et al. 1981).

"The unexpected finding of a lower death rate in the exposed people was interpreted by Mine et al. (1981) as a ‘healthy survivor’ effect (Section 2.3.2). To exclude any such effect, Mine et al. (1990) compared mortality rates among subgroups of health handbook holders classified by dose of exposure to bomb radiation. Since 1970, data on 100,000 atomic bomb survivors with the health handbook have been maintained at the Scientific Data Center for the Atomic Bomb Disaster at Nagasaki University School of Medicine. Information was selected from this data base on 3,456 people who had been exposed to known doses, and mortality during 1970-88 in this selected group (observed) was compared with that of an age-matched control group (expected) who were given the health handbook but lived far from the hypocenter of the Nagasaki bombing (see footnote b to Table 3.2).

Figure 3.1

"The ratio of observed: expected numbers of deaths show that the mortality of exposed people was slightly lower than or equal to that of unexposed people at all four low to intermediate doses, 1-49, 50-99, 100-149 and 150-199 rad, and that a significant increase in deaths occurred only in the high dose range, 200-599 rad (Table 3.2). "The apparent absence of harmful effects of low doses of radiation was analyzed by determining the observed: expected numbers of people classified according to cause of death, sex and dose. As shown in Figure 3.1 and Table 3.3, doses of 50-99 rad significantly reduced the number of deaths from all causes except cancer, to 65% of the control value. On the other hand, the number of deaths from cancer increased at all dose levels except 1-49 rad, although the increase was not statistically significant. Thus, low doses of radiation had two opposite effects—beneficial and harmful—on the human life span in Nagasaki after the atomic bombing."

"If we were to take the observed expected ratios for mortality from all causes given in Table 3.2 at face value, we would be forced to conclude that whole-body irradiation with 50-150 rad (actually 40-110 rad after correction for the systematic error in the T65D dosimetry had a beneficial effect on the survival only of men—a decrease in overall mortality of about 10%. This level of radiation, however, caused about a 40% (non-significant) increase in deaths from cancer in men (Table 3.2) and higher levels had harmful effects on both men and women.

"The slight but non-significant decrease in mortality among bomb survivors exposed to low and intermediate doses (6-19, 20-49, 50-99 and 100-199 rad) of radiation was seen as early as 1950-55... Table 3.4 is taken from a recent report by Shimizu et al. (1992), which is based on the follow-up studies that have been conducted since 1950 by the Atomic Bomb Casualty Commission (1950-74) and the Radiation Effects Research Foundation (RERF) (1975) on a fixed cohort of about 75,000 atomic bomb survivors in Hiroshima and Nagasaki and 35,000 suitable controls.

"It is interesting to note from the Table that the seemingly beneficial effects of low to intermediate doses of radiation are larger in men than in women. This finding is in agreement with the conclusion of Mine et al. (1990), and reflects the experimental finding that daily whole-body irradiation of mice at 0.1 rad significantly increased the mean survival time of males, despite significant increases in the incidence of cancers, from 684 +-14 days in controls to 783 +-14 days after irradiation, whereas females irradiated in the same way showed a slight but insignificant increase in mean survival from 803 +-16 days in controls to 820 +-18 days after irradiation (Lorenz et al., 1955). Thus, the males in this experiment appeared to be more sensitive to the ‘beneficial’ effects of low-level radiation than females."

Table 3.1 Observed and expected annual rates of deaths (1970-76) from all causes among atomic bomb survivors in Nagasaki

Table 3.2 Initial numbers of subjects (1970), observed (O) and expected (E) numbers of deaths from all causes and relative risk during 1970-88 among atomic bomb survivors in Nagasaki classified by dose and sex

Table 3.3 Observed (O) and expected (E)^a numbers of deaths during 1970-88 in Nagasaki among atomic bomb survivors classified by cause of death, sex and dose

Table 3.4 Relative risk for mortality from all diseases except neoplasms and hematological conditions among atomic bomb survivors, 1950-85 by sex

(from Shimizu et al., 1992. Copyright Academic Press, Orlando. Reproduced with permission)