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

1.9
Conclusions

"Significant positive health effects associated with low level radiation have been demonstrated in a review of five epidemiologic studies: decreased mortality of nuclear shipyard workers, decreased non-cancer mortality of atomic bomb survivors in both Hiroshima and Nagasaki and Nagasaki alone, decreased lung cancer mortality associated with increased radon exposure of the U.S. population, and decreased breast cancer mortality of women in Canada after having received multiple fluoroscopic examinations. The tendency to neglect or reject data that contradicts the linear-no threshold theory of radiation carcinogenesis is supported by confidence that chromosome aberration and gene mutation can be produced by a single particle of ionizing radiation and so initiate a malignancy. The number of such interactions with cell nuclei is both logically and demonstrably proportional to the dose. However, no consideration is given to biological defense mechanisms that could be stimulated further by low level increments of radiation above the background level. Such stimulated defense mechanisms could also decrease carcinogenesis by chemical and other non-ionizing agents as well as high level ionizing radiation. Multiple defense mechanisms at molecular, cellular, organ, and systemic levels involving enzymatic, hormonal, immunologic, and stress protein interactions are currently being demonstrated and confirmed by numerous investigators (21 refs).

"Recently a human radiation repair gene has been cloned and transfected into a mutant Chinese hamster with sensitivity to both ionizing radiation and certain alkylating agents resulting from defective repair of DNA strand breaks. These transfected mutants demonstrate overexpression of the human DNA repair minigene with repair capacity increased above that of the wild-type Chinese hamsters."

"Mounting reproducible evidence of the operation of various defense mechanisms and their stimulation by low dose ionizing radiation will provide further details of how biological defense mechanisms, non-operative at high doses, are stimulated and enhanced by low level radiation damage so as to overcorrect and predominate. These investigations have clarified why the negative health effects observed at high levels of radiation that effectively overwhelm these defense mechanisms cannot be extrapolated to the low

levels in which these stimulated defense mechanisms predominate with decreased cancer induction, decreased mortality, and other observed positive health effects."