LAUSR

The framework of protection against the adverse health effects consequent to low levels of exposure to ionizing radiation as recommended by the International Commission on Radiological Protection (ICRP) [1] addresses the risks of cancer in the exposed individual and hereditary effects in subsequently conceived offspring (and their descendants). Somatic diseases other than cancer do not feature in the scheme of protection against stochastic effects, because they are not considered to be related to low doses or low dose-rates of radiation [1]. Of particular importance is the risk of diseases of the circulatory system (DCS), such as heart attacks and strokes, and the ICRP has inferred that the absorbed dose threshold for DCS may be as low as 0.5 Gy to the heart or brain [2], although more recent evidence suggests that an excess risk may be present at lower levels of exposure [3]. DCS are the leading cause of death globally [4], so even a small proportional increase in DCS risk could have a material impact on the overall numbers of excess radiation-related deaths [2, 5]. The long-term health experience of the Japanese survivors of the atomic bombings of Hiroshima and Nagasaki in 1945 provides impressive evidence of the late effects of whole-body exposure to (primarily) gamma radiation, and this includes DCS. The fact that acutely delivered high doses cause an increased risk of DCS through tissue damage is not unexpected [2, 6], but there are indications that radiation-related risks among the atomic bomb survivors extend to lower doses [2, 7]. However, Ozasa et al [8] suggest that the patterns of DCS incidence and mortality in the survivors should be interpreted cautiously because of other (non-radiation-related) influences on DCS risk and historical variations in disease classification. Furthermore, the survivors are a Japanese population acutely exposed to radiation from a nuclear explosion in the mid-20th century at the end of a long war, so additional sources of evidence are desirable. This is where studies of those exposed in the workplace are of considerable value because radiation workers experience protracted exposure to low dose-rates.