What lifelong study of atomic bomb survivors tells us about radiation

Fear of radiation is an important part of the post-World War II era. Assumptions about the link between radiation exposure and the risks of cancer and birth defects remain widespread in almost every part of the world. However, the most enduring source of this fear has a story to tell that deserves to be heard.

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

Their future became an open medical question. Scientists feared that the radiation they received, especially the significant levels of gamma rays and neutrons, could cause waves of leukemia, birth defects and hereditary diseases. In the cultural imagination, radiation became irrevocably linked to cancer, disfigurement and death.

But as the decades progressed, careful and sustained research revealed a more complex and different reality. About 120,300 survivors – men, women and children – who continued to live in the area of ​​the bombed cities agreed to take part in a large-scale action. Lifespan studymonitoring their health and that of their offspring. It followed them not as data points, but as people who created ordinary human lives under extraordinary historical circumstances.

The LSS is led by Japanese and American researchers and continues today. It constitutes the most comprehensive data set ever collected on the effects of radiation exposure in humans. As such, it provides an important scientific basis for understanding the true risks associated with such exposure.

What recent interpretation of data now shows

Data from the LSS has been newly analyzed to determine in particular the number of cancer deaths resulting from the two bombings. While consistent with other long-term studies of radiation exposure, the findings are likely to be surprising – perhaps even astounding – to many people, even scientists in unrelated fields.

Here’s what they show: Radiation increased the risk of cancer among survivors, but the magnitude of the increase is small: About 1% to 2% percent of all deaths among survivors can be attributed to radiation-induced cancers.

Leukemia was the first to show a clear increase. The cases began appearing about two years after the bombings, peaking about 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 lungs, stomach, breast and other organs – appeared much later, reflecting the slower development of these diseases. In the period from 1950 to 2003, approximately 500 excess deaths from solid cancers were linked to radiation exposure. When projected over the lives of the survivors, the total rises to about 1,500 cases.

Although these figures represent real suffering, they also offer perspective. In the same population, more than 10,000 people died from cancer unrelated to radiation. Mortality research of solid cancers in Japan since 1940 show a significant increase whose risk factors are related to smoking and diet.

The additional risk to LSS subjects was much 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 average life expectancy is about 78 years – comparable to or even slightly higher than life expectancy in several developed countries at the turn of the 21st century. Most survivors lost an average of about six weeks of their lives due to radiation exposure.

Just as important is what happened not to happen. Decades of research have found no detectable increase in birth defects or inherited genetic disorders in the children of survivors. This finding – once uncertain and a source of fear – has endured for generations.

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

Clearly understand the legacy

To say that the long-term health effects of radiation were limited is not true not to minimize the suffering suffered. Survivors of the bombings of Hiroshima and Nagasaki carried physical scars, memories of chaos and grief with them throughout their lives.

But the scientific record is important. It does indeed matter a lot. What the survivors experienced after the bombings was not lifelong medical decline. It was a collective effort to rebuild lives, households, neighborhoods and identities. Hiroshima and Nagasaki are thriving cities today not only because they have been rebuilt, but also because the people who lived through the destruction continue to shape the future of each urban area.

Clearly understanding this legacy is important not only for the history of the bombings, but also 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 the long-term physical risks of radiation are likely to be modest, even after a catastrophe.

One final point

The world owes a debt of gratitude to the people of the LSS. Although formal informed consent was not originally obtained and such standards were lacking prior to the 1964 Declaration of Helsinki, participants have continued to participate voluntarily in the study to this day, with many individuals expressing the hope that all data would be used for the benefit of humanity and peace.

This is all the more significant as they suffered from a significant degree of social stigma from the society in which they lived. Known as hibakusha– literally ‘victims of the bomb’ – faced discrimination in personal relationships, marriage, employment and in everyday life in general. More than a few faced social rejection and isolation, a situation shared by their children. Others tried to keep this part of their identity a secret, but faced repercussions if it was discovered.

A major reason for this stigmatization was the misconception that most people had about radiation – that survivors were infected, carriers of hereditary damage that could be contagious, who would pass on physical deformities and diseases to their offspring, and thus in a sense pollute Japanese society itself.

The fact 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 must be allayed by the simple facts that over 99,000 officially recognized survivors are still alive today, on average 86 years old, with healthy children, grandchildren and, in more than a few cases, great-grandchildren.