The study authors, however, were quick to point out that radiation exposure itself may not be directly responsible for the increase in circulatory problems among nuclear industry workers.

Yet the UK report adds to growing health concerns surrounding the nuclear industry that have been mounting in the last four months. In December, a German study reported that the incidence of childhood leukaemia more than doubles in populations residing in the vicinity of nuclear power plants.

The UK study of 65,000 nuclear industry workers over a period of more than 60 years was published in the International Journal of Epidemiology by Westlakes Scientific Consulting, a private company hired by British Nuclear Fuels and the Nuclear Decommissioning Authority to carry out the research.

The link was particularly surprising, noted the study, because there is no established biological mechanism that would explain how radiation exposure might cause heart disease. As a caveat against blaming radiation outright, the study noted that nuclear workers’
job-related stress or irregular shift patterns may also contribute to increased levels of heart disease.

The research team, led by Westlakes Scientific Consulting’s Professor Steve Jones, studied 64,818 workers at the Sellafield, Springfields, Chapelcross and Capenhurst nuclear sites in the UK. Some of the workers began work in the industry as far back as 1946, and 42,426 were exposed to radiation as part of their job.

When the researchers compared UK workers occupationally exposed to radiation with those who were not, they did not find any difference in the number of cases of heart disease and stroke.

However, when they split the radiation-exposed workers into groups with different levels of exposure – based on readings from radiation-monitoring badges worn by all staff – a disparity emerged.

Those workers who were exposed to the highest levels had a slightly lower life expectancy due to an increased probability of heart disease and strokes.

"We see a higher mortality for those workers with the highest level of operation exposure," Jones told The Guardian.

The team stressed that because the analysis was carried out retrospectively, it could not be sure that the findings ruled out other factors that could be responsible for the results.

"We can’t show whether it’s a consequence of that exposure or whether it’s due to something else," said Jones.

However, he added that if radiation were the cause, then the workers who have experienced the highest levels of exposure have roughly a 73% chance of surviving until they are 70, compared with a 75% chance if they had received no exposure at all.

The report is of little concern to those who have joined the nuclear industry workforce recently, another report author, Michael Gillies, said.

"I don’t think it’s a big issue for nuclear workers at present or in the future because the exposure levels are so low," Gillies was quoted by The Guardian as saying.

The most highly exposed workers, noted the report, received a radiation dose around five to 10 times less during their entire working lives than survivors of the atomic bomb dropped on Hiroshima in 1945.

Yet, another surprising outcome of the study is that British nuclear workers, despite the dangers they face on the job, are healthier on average than the general population living in the area of the nuclear installations studied. By comparing their sample with the average for the local population, the research team found that the mortality rate of nuclear workers is 20 percent lower.

Jones warned that further study is required before a positive link between high radiation exposure and heart disease and other circulatory problems can be firmly established.

But Professor Dudley Goodhead, former Director, MRC Radiation and Genome Stability Unit – which studies cellular function and radiation related disease – said that the heart disease link to high radiation exposure is emerging in other studied groups as well.

“In more recent year, continuing follow-up of the survivors of the atomic bombs in Japan have shown that acute exposure to radiation are associated with an increase in the rate of death from heart disease also,” Goodhead told the Telegraph.

"The findings of the present study clearly suggest that even chronic exposure to radiation, spread over long periods of time such as received by some radiation workers in the past, may also be able to cause increased heart disease,” said Goodehead.