From Hiroshima and Nagasaki to Fukushima 1 Long-term eff ects of radiation exposure on health

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 eff ects 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 defi nitively. This outstanding issue is not only a problem when dealing appropriately with potential health eff ects 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 eff ects of low doses of radiation needs to be established.