TUCSON, Ariz., Dec. 14, 2017 /PRNewswire-USNewswire/ -- High-dose ionizing radiation is known to reduce the body's resistance to cancer, but low-dose radiation actually enhances natural defenses, writes Bobby R. Scott, Ph.D., in the winter issue of the Journal of American Physicians and Surgeons. This means that the widely believed statement that "there is no safe dose of radiation" is not true.
Scott, a scientist emeritus at the Lovelace Respiratory Research Institute in Albuquerque, N.M., points out in this review that natural background radiation is estimated to have been five-fold higher in earlier eras, and mammals likely survived because of enhanced natural cancer barriers.
All the cells in the body are constantly subjected to damage from reactive oxygen species generated through normal metabolic processes. Radiation injury results from the same mechanism. Without sophisticated molecular defense mechanisms, the cell would soon die from unrepaired damage to DNA, enzymes, and other cellular components.
One defense is "antioxidant" enzymes that deactivate reactive oxygen species. As revealed in animal studies, levels of these enzymes increase in response to whole-body exposure to low and moderate doses of ionizing radiation.
The most serious type of damage is double-strand breaks in DNA. These increase linearly with dose, and this relationship led to the false belief that cancer induction is also a linear no-threshold function of radiation dose, i.e. that any dose can increase the risk of cancer. However, DNA double-strand break repair is activated by low radiation doses, producing a protective natural barrier to mutation-related harm.
This "adaptive response" at low doses also reduces the frequency of spontaneous mutations, unlike high doses, which increase the frequency. An entity that causes harm at high levels but protection at low levels is said to have a hormetic dose-response relationship, Scott explains.
Scott also reviews experimental evidence for additional protective effects induced by low-level regulation, including epigenetic regulation of gene expression, cellular senescence, selective removal of aberrant cells, tissue-level interactions, suppression of cancer-facilitating inflammation, and enhancement of anti-cancer immunity.
Together, the indicated protective effects (cancer barriers), when activated by low-dose ionizing radiation, can reduce the frequency of cancer to well below the background level.
Scott concludes that low doses of ionizing radiation are more likely to be beneficial rather than harmful.
The Journal of American Physicians and Surgeons is published by the Association of American Physicians and Surgeons (AAPS), a national organization representing physicians in all specialties since 1943.
SOURCE Association of American Physicians and Surgeons (AAPS)