Nuclear workers exposed to high levels of radiation before the 1980s appear to be at increased risk from heart attacks and other circulatory problems, according to a study of 65,000 British Nuclear Fuels Limited (BNFL) employees. However, other interlinked factors such as shift work have not been ruled out.
The workers were employed at BNFL’s Capenhurst, Chapelcross, Sellafield and Springfields sites between 1946 and 2002. All wore dosimeter badges which measured their radiation exposure.
The average exposure of a blue-collar worker at these sites has fallen from around 10 millisieverts (mSv) per year in the 1950s to about 1mSv/year in 2000. This is lower than the 2.5mSv background-radiation level in the area around Sellafield.
The study found a 65% increase in risk of death from circulatory disease and a 70% increase in heart disease per sievert of cumulative occupational radiation exposure. However, only about 4% of workers exceeded a cumulative exposure of 400mSv.
"What we have shown is an association between relatively high levels of occupational exposure to radiation and mortality from circulatory system disease," said Professor Steve Jones of Westlakes Scientific Consulting, the Cumbrian consultancy behind the study. "However, we have not been able to take account of all the other possible causes of circulatory system disease.
"We also found an overall ‘healthy worker’ effect - that is, workers had lower mortality rates that the local general population."
There is a well-established link between exposure to ionising radiation and most types of cancer. But while studies of atomic bomb survivors and radiotherapy patients have linked short periods of intense radiation exposure to heart disease, studies on long-term exposure are more ambiguous.
Acute exposure studies suggest large radiation doses can damage blood vessels and cause inflammation, which encourages arterial plaques to form. For chronic exposure, the cause of damage is less clear but one suggestion is that the radiation may create mutagenic plaques.
Other factors that may be behind the link found at BNFL include socioeconomic status, shift work and exposure to particular chemicals, said Westlakes. There is preliminary evidence against most of these factors, but more investigation is needed.