The risk of heart disease or stroke from low dose radiation like that used in hospital or dental X-rays may have been significantly underestimated, a new study partly funded by the European Commission says. The results, which were published last week in the journal Public Library of Science (PLoS) Computational Biology, are consistent with risk levels reported in previous radiation studies involving nuclear workers. The research team at Imperial College London, UK, constructed a mathematical model to predict the risk of cardiovascular disease associated with low-level radiation. Results showed that the risk of coronary heart disease and stroke, the two main causes of death in the developed world today, vary in proportion with the dose of radiation. The study is part of the five-year EU-funded project CARDIORISK ('The mechanisms of cardiovascular risks after low radiation doses'), which received funding of EUR 3.8 million under the EURATOM-FISSION Thematic area of Seventh Framework Programme (FP7). Heart disease and stroke leading to death and disability are causing a huge economic burden on health care organisations throughout the developed world. In the UK alone, heart disease is the single greatest cause of death, killing more than 125,000 people prematurely every year. Dietary factors are often implicated in heart disease, but the authors of the study say there is evidence of an increase in 'occupationally exposed' groups such as nuclear workers. Scientists have known for some time that higher levels of cardiovascular disease are observed in many groups of patients who have received high dose radiotherapy treatment, as radiotherapy can cause inflammation of the heart and arteries, but recent studies have shown connections between cardiovascular disease and much lower doses of radiation in groups such as nuclear workers. The reasons explaining these connections are not yet known. Dr Mark Little and the research team at Imperial College London explored the hypothesis that radiation kills monocytes (a type of white blood cell) in the walls of arteries which would otherwise bind to monocyte chemo-attractant protein 1 (MCP-1). As a result, the higher levels of MCP-1 cause inflammation that leads to cardiovascular disease. The authors of the study said, 'There is emerging evidence of excess risk of cardiovascular disease in various occupationally exposed groups, exposed to fractionated radiation doses with small doses/fraction. The mechanisms for such effects of fractionated low-dose radiation exposures on cardiovascular disease are unclear.' Further research is now planned on radiation-induced heart disease to uncover the biological processes behind it.