Mortality from heart diseases following occupational radiation exposure: Analysis of the National Registry for Radiation Workers (NRRW) in the United Kingdom

Statistically significant increases in heart disease (HD) mortality with cumulative recorded occupational radiation dose from external sources were observed among 174 541 subjects, who were predominately exposed to protracted low doses over a number of years, and were followed up until the end of 2011 in the UK National Registry for Radiation Workers (NRRW) cohort. Amongst the subtypes of HD, the increasing trends with cumulative dose arose for ischaemic heart disease (IHD) and other HD (which includes pulmonary HD, valve disorders, cardiomyopathy, cardiac dysrhythmias, carditis, conduction disorder and ill-defined HD). For IHD, the increased mortality appears to be at least 20 years after first exposure and the excess risk peaked between 30 and 40 years after the first exposure. There was no evidence of excess risk of IHD mortality for cumulative radiation doses below 0.1 Sv. A categorical analysis also showed that the risk falls below the expected value based on a linear trend, for cumulative doses greater than 0.4 Sv; this smaller risk appears to be primarily associated with workers who started employment at a younger age and who were employed for longer than 30 years, reflecting possible healthy worker survivor effect. This analysis provided further evidence that low doses of radiation exposure may be associated with increased risk of IHD. For other HD, the data suggest an increased risk starting around 40 years after the first exposure. The risk was statistically significant raised only for cumulative doses above 0.4 Sv. However, the number of deaths in this group was small and the results need to be interpreted with caution.