"Low Level
Radiation Health Effects: Compiling  the Data"

Revision 2
March 19, 1999

by Radiation, Science, and Health, Inc.,
Edited by J. Muckerheide

1.3
Animal & Plant
Biology

1.3.1
Mammals

References

"Evidence supporting the idea of radiation hormesis can be divided into four broad categories: (1) experiments with plants or animals; (2) human occupational comparisons; (3) regional studies; and (4) experiments throwing light on the effect of radiation at the molecular level."

"The first pieces of experimental evidence supporting the idea of radiation hormesis derive from the early research of Atkinson (1898) and Davey (1919) referred to above. In more recent times, experiments with animals have been conducted by the (US) National Cancer Institute, for instance. Those carried out in the early 1940s, for example, pointed to a rather unexpected relationship: the irradiated animals had a slightly longer mean life span and greater weight gain than their non-irradiated controls (Henry 1961). Similarly, animal experiments carried out by Lorenz and his associates in 1955 (Henry 1961) indicated that exposure of both mice and guinea pigs to 0.11 r per day of radium gamma increased their average life span by about 7 %, whereas exposures of 1.1 r per day slightly reduced it. Summarizing the results of a large number of animal experiments, Henry arrived at a positive view of the radiation hormesis hypothesis: 'The preponderance of data better supports the hypothesis that low chronic exposures result in an increased longevity than it supports the opposite hypothesis of decreased longevity' (Henry 1961). Similarly, Sagan (1989), after summarizing a large number of animal experiments, including those of Congdon (1987), concluded that 'many experimental studies (but not all) have shown that laboratory animals exposed to low doses of radiation outlive unexposed controls' ".