What Lifelong Study Of Atom Bomb Survivors Tells Us About Radiation

HIROSHIMA, JAPAN – AUGUST 5: 80 year-old atomic bomb survivor, Sunao Tsuboi holds a picture taken 3 hours after the bomb was dropped. (Photo by Junko Kimura/Getty Images)

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Fear of radiation is a staple of the post-WWII era. Assumptions about links between radiation exposure and risks for cancer and birth defects remain widely held in almost every part of the world. The most enduring source of this fear, however, has a story to tell that should be heard.

Nearly eighty years after the atomic bombings of Hiroshima and Nagasaki, the images remain etched in human memory: a blinding flash, the soaring mushroom cloud, cities reduced to plains of ash. The suffering was immediate and immense—tens of thousands killed in seconds, many more dying in the days that followed. Yet behind those scenes were also hundreds of thousands of people who were exposed to radiation but did not die.

Their futures became an open medical question. Scientists feared the radiation they’d received, especially the significant levels of gamma rays and neutrons, might trigger waves of leukemia, birth defects, and inherited illness. In the cultural imagination, meanwhile, radiation became irretrievably linked with cancer, deformity, and death.

But as the decades unfolded, careful and sustained research revealed a more complex and different reality. Around 120,300 survivors—men, women, and children—who continued to live in the area of the bombed cities agreed to participate in a massive Life Span Study, tracking their health and that of their descendants. It followed them not as data points, but as people who established ordinary human lives under extraordinary historical circumstances.

Conducted by Japanese and American researchers, the LSS continues today. It forms the most comprehensive dataset ever collected on the effects of radiation exposure in human beings. As such, it forms a key scientific foundation for understanding the true risks associated with such exposure.

What Recent Interpretation Of Data Now Shows

Data from the LSS have been newly analyzed to determine, in specific, the numbers of cancer deaths that have resulted from the two bombings. Though consistent with other long-term studies of radiation exposure, the findings are likely to be surprising—perhaps even astonishing—to many people, even to scientists in unrelated fields.

This is what they show: radiation did increase the risk of cancer among survivors, but the scale of the increase is small—about 1%-2% percent of all deaths among survivors can be attributed to radiation-induced cancers.

Leukemia was the first to show a clear rise. Cases began appearing about two years after the bombings, peaking roughly a decade later before tapering off. In total, radiation exposure caused an estimated 160 deaths from leukemia among the main survivor group.

Solid cancers—tumors of the lung, stomach, breast, and other organs—appeared much later, reflecting the slower development of these diseases. Over the period from 1950 to 2003, roughly 500 additional deaths from solid cancers were linked to radiation exposure. When projected over survivors’ lifetimes, the total rises to around 1,500 cases.

While those numbers represent real suffering, they also offer perspective. In the same population, more than 10,000 people died from cancers unrelated to radiation. Studies of mortality from solid cancers in Japan since 1940 reveal a significant rise whose risk factors are related to smoking and to diet.

The additional risk for LSS subjects was far smaller than once feared. Perhaps the most striking finding is that survivors generally lived long lives. Even among those who had received doses high enough to cause radiation sickness in 1945, the median life expectancy is around 78 years—comparable to or even slightly exceeding life expectancy in several developed countries at the turn of the 21st century. Most survivors lost, on average, about six weeks of life due to radiation exposure.

Just as significant is what did not happen. Decades of study found no detectable increase in birth defects nor inherited genetic disorders among the children of survivors. This finding—once uncertain and a source of dread—has held firm for generations.

It dismantles one of the most persistent myths about radiation: that it inevitably brings inherited, long-term biological ruin.

Understanding the Legacy Clearly

To state that radiation’s long-term health effects were limited is not to minimize the suffering that occurred. Survivors of the Hiroshima and Nagasaki bombings carried physical scars, memories of chaos, and grief that endured throughout their lives.

But the scientific record matters. Indeed, it matters greatly. What the survivors experienced after the bombings was not a lifelong medical degradation. It was a shared effort to rebuild lives, households, neighborhoods, and identities. Hiroshima and Nagasaki today are thriving cities not only because they were reconstructed, but because the people who lived through the destruction continued to shape the future of each urban area.

Understanding this legacy with clarity is important, not only for the history of the bombings, but for the way society thinks about radiation today. The fear of radiation has long extended beyond the scientific evidence of its effects. While the context and details of exposure are always crucial, the story of Hiroshima and Nagasaki shows that radiation’s long-term physical risks are likely to be modest—even after catastrophe.

A Final Point

To the people of the LSS the world owes a significant debt of gratitude. Though formal, informed consent was not originally acquired, such standards being absent prior to the 1964 Declaration of Helsinki, participants have voluntarily continued to be part of the study down to the present, many individuals expressing their hope that any data be used for the benefit of humanity and peace.

This is all the more meaningful, given that they suffered a considerable amount of social stigma from the society in which they lived. Known as hibakusha—literally, “victims of the bomb”—they faced discrimination with regard to personal relationships, marriage, jobs, and in daily life overall. More than a few faced social rejection and isolation, a situation also shared by their children. Others tried to keep this part of their identity secret but then faced repercussions if it was discovered.

A key reason for this stigmatization was the misconception most people had about radiation—that survivors were contaminated, carriers of hereditary damage that might be contagious, that would pass on physical deformities and illness to their descendants, thus, in a sense, polluting Japanese society itself.

That the bomb survivors as a group were awarded the Nobel Peace Prize in 2024 cannot erase the years of such treatment. The fears behind such treatment should be dispelled by the simple facts that over 99,000 officially recognized survivors are alive today, averaging 86 years in age, with healthy children, grandchildren, and, in more than a few cases, great-grandchildren.