Late-onset effects of exposure to ionising radiation on the human body have been identified
by long-term, large-scale epidemiological studies. The cohort study of Japanese survivors
of the atomic bombings of Hiroshima and Nagasaki (the Life Span Study) is thought
to be the most reliable source of information about these health effects because of
the size of the cohort, the exposure of a general population of both sexes and all
ages, and the wide range of individually assessed doses. For this reason, the Life
Span Study has become fundamental to risk assessment in the radiation protection system
of the International Commission on Radiological Protection and other authorities.
Radiation exposure increases the risk of cancer throughout life, so continued follow-up
of survivors is essential. Overall, survivors have a clear radiation-related excess
risk of cancer, and people exposed as children have a higher risk of radiation-induced
cancer than those exposed at older ages. At high doses, and possibly at low doses,
radiation might increase the risk of cardiovascular disease and some other non-cancer
diseases. Hereditary effects in the children of atomic bomb survivors have not been
detected. The dose-response relation for cancer at low doses is assumed, for purposes
of radiological protection, to be linear without a threshold, but has not been shown
definitively. This outstanding issue is not only a problem when dealing appropriately
with potential health effects of nuclear accidents, such as at Fukushima and Chernobyl,
but is of growing concern in occupational and medical exposure. Therefore, the appropriate
dose-response relation for effects of low doses of radiation needs to be established.