In August 1945, the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki. The unprecedented explosions and resulting radioactive fallout resulted in the tragic deaths of roughly 200,000 people.

High levels of ionizing radiation spawned by the detonations sentenced individuals who survived the initial blasts to various cancers. Strangely, however, survivors subjected to lower doses of radiation may actually have had elongated lifespans and reduced cancer mortality. Such is the finding of an article recently published to the journal Genes and Environment.

Researcher Shizuyo Sutou of Shujitsu Women's University is the author of the paper. Sutou examined data from the Life Span Study, which has followed 120,000 survivors of the atomic bomb blasts since 1950. His analysis showed that survivors exposed to between 0.005 and 0.5 Grays of radiation (just before where light radiation sickness starts) had lower relative mortality than control subjects not exposed to atomic bomb radiation.

The green line in the chart shows radiation's association to cancer risk according to the hormetic theory.

Sutou's finding is in line with the hormetic theory of radiation (hormesis), which states that very low doses of ionizing radiation might actually be beneficial, producing adaptive responses like stimulating the repair of DNA damage, removing aberrant cells via programmed cell death, and eliminating cancer cells through learned immunity.

Radiation hormesis is backed by a number of studies, but it is currently not accepted by organizations like the National Academy of Sciences or United Nations Scientific Committee on the Effects of Atomic Radiation, which support the linear no-threshold (LNT) model of radiation protection. This model effectively states that any dose of ionizing radiation is harmful. Scientists like Carol Marcus, a Professor in Nuclear Medicine at UCLA, thinks this stance is overly cautious to the point of itself being hazardous. Irrational fear of radiation, no matter the amount, is counterproductive, she says.

"Forced evacuations in Fukushima have caused some 1600 premature deaths; forced evacuees from Chernobyl have a higher death rate than the 'babooshkas' who returned to the area despite government policy against it," she wrote, referencing studies suggesting that potentially unnecessary Fukushima evacuations disrupted healthcare services.

"Patients are refusing diagnostic nuclear medicine and radiology procedures that are needed for diagnosis and disease management. Parents are refusing to let their children undergo needed diagnostic nuclear medicine and radiology studies," she added.

Hormesis is difficult to study in the lab – is it ethical to dose people with radiation without knowing how much is harmful or beneficial? Sutou's new findings strengthen the case for radiation hormesis, but it likely won't be enough to change current no-tolerance policies on radiation exposure.

Source: Shizuyo Sutou. Low-dose radiation from A-bombs elongated lifespan and reduced cancer mortality relative to un-irradiated individuals. Genes and Environment 2018 40:26. https://doi.org/10.1186/s41021-018-0114-3