Low doses of radiation associated with a small excess risk of developing cancer

Low doses of radiation, such as those received in the nuclear industry, are associated with a small excess risk of developing cancer, according to a study published online by the BMJ today.

This is the largest study of nuclear industry workers ever conducted and brings together the largest body of evidence to date concerning the effects of low dose chronic exposure to ionising radiation.

Ionising radiation is one of the most studied and ubiquitous carcinogens in our environment. Current radiation protection recommendations are to limit occupational doses to 100 millisieverts (mSv) over five years and doses to the public to 1 mSv per year. These standards are based mainly on data from survivors of the atomic bomb in Japan and the extrapolation of risks to the general population and radiation workers is controversial.

The study involved over 407,000 nuclear industry workers in 15 countries. The workers, most of whom were men, were employed for at least one year in nuclear power production facilities, or in specialised activities including research, waste management, and production of fuel, isotopes, and weapons.

Workers were monitored for external radiation exposure and were followed-up for 13 years on average.

Risk estimates per level of radiation dose were then calculated for deaths from all cancers excluding leukaemia and from leukaemia excluding chronic lymphocytic leukaemia. Factors such as age, duration of employment, and socioeconomic status were taken into account.

The team estimates that a cumulative exposure of 100 mSv, would lead to a 10% increased risk of mortality from all cancers excluding leukaemia and a 19% increased mortality from leukaemia excluding chronic lymphocytic leukaemia.

On the basis of these estimates, they suggest that 1-2% of deaths from cancer among workers in this study may be attributable to radiation.

They note, however, that many of the workers in this study worked in the early years of the industry when doses tended to be higher than they are today. Only a small proportion of cancer deaths would be expected to occur from low-dose chronic exposures to X- and gamma- radiation among current nuclear workers and in the general population.

The risk estimates from the study are consistent with those used for current radiation protection standards, they say. These results suggest that a small excess risk of cancer exists, even at the low doses typically received by nuclear industry workers in this study.

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