RSH Data & Documents

"Low Level
Radiation Health
Effects: Compiling
the Data"

Revision 2
March 30, 1999
by Radiation, Science, and
Health, Inc.,
Edited by J. Muckerheide

1.2.1.5 Longevity

"In 1958, in spite of the critique of the linear hypothesis of carcinogenesis by Brues (1958) and many others, the first report by the United Nations Scientific Committee on the Effects of Atomic Radiation (1958) accepted the no-threshold hypothesis that radiation is hazardous however small doses. Since then this hypothesis has been widely accepted. Based on this hypothesis, radiation protection practices have presumed low-dose risk estimated by linear extrapolation from observed high-dose effects (ICRP 1977). Risk estimates based on this hypothesis have been recently used to assess hazard to humans of natural radon (Clarke and Southwood 1989) and the Chernobyl fallout (Anspaugh et al 1988). However, the validity of the no-threshold model has seldom been critically assessed with actual data on humans exposed to low doses. Jablon et al (1965), Beebe et al (1978) and Kato et al (1982) continued studies on mortality (1950-1978) of a large cohort of A-bomb survivors in Hiroshima and Nagasaki, which we hereafter call the RERF (Radiation Effects Research Foundation) population, and concluded that low doses of A-bomb radiation caused no harmful effects other than cancers, but made no comments on their findings that death rates from all causes frequently showed seemingly lower values in persons exposed to low doses than in unexposed persons. The importance of this U-shaped dose-response relationship was first pointed out by Stewart and Kneale(1984). Using a more recent report on mortality of the RERF population, Stewart and Kneale (1988) noted that deaths in 1950-1982 from all non-malignant diseases were significantly lower in survivors exposed to low doses than in unexposed persons. The present paper reports a similar 'seemingly beneficial' effect of low doses in a cohort of Nagasaki A-bomb survivors; they are considerably different from the Nagasaki survivors included in the RERF population."

"Since 1970, a database of about 100,000 A-bomb survivors in Nagasaki has been maintained at the Scientific Data Center for the A-Bomb Disaster at Nagasaki University School of Medicine (Okajima et al 1985).... From the data, we selected those for a total of 3456 exposed persons and a total of 3x3456 age-matched controls who were alive in 1970. The distributions of these subjects and total deaths (1970-1988) in the exposed group (O) and in the control group (E) are classified according to sex and dose. ... Expected deaths (E) were estimated from deaths of persons living far from the center of A-bomb radiation in Nagasaki at the time of the A-bomb explosion."

"The O/E ratio in Table 1 shows that mortalities from all causes for male subjects exposed to 1-49, 50-99, 100-149 and 150-199 cGy, were slightly lower than, or almost equal to, those of unexposed persons, and that radiation-induced mortality was evident only in the group exposed to 200-599 cGy.

Table I

"Because of this apparent absence of harmful effects of low to intermediate doses of radiation in males, were examined the O:E ratios of persons classified according to 50-99 cGy showed significant reduction in death from all diseases other than cancer.

"To obtain a different line of evidence for the suggested beneficial effect of 50-99 cGy in males, the validity of the U-shaped dose-response relationship for deaths of males from non-cancerous diseases indicated by the O:E ratios in Table 2, was tested by logistic regression method (Breslow and Day 1984)."

Table II

"Holders of A-Bomb Health Book i.e. A-bomb survivors in Nagasaki, showed significantly lower age-specific death rates (1970-1976) than normal residents in Nagasaki without an A-Bomb Health Book (Mine et al 1987).

"The present preliminary study of human data is compatible with low doses of radiation having beneficial effects under certain conditions. This conclusion is consistent with many other lines of evidence supporting the concept of radiation hormesis, that low doses of radiation are not necessarily harmful to living things but, on the contrary, may be stimulatory, like hormones (Roessler 1987; Feinendegen et al 1994; James and Makinodan 1988; Kondo 1988a & b; Kondo 1990).