Chronic low-dose exposure to radiation such as that associated with work in nuclear-related industries causes a slight increase in cancer risk, according to a major international study published online June 29th by the British Medical Journal.

The current research involved over 407,000 former and current workers in nuclear-related industries in 15 different countries. Workers were monitored for external radiation exposure and followed for an average of 13 years.

The employees, most of whom were men, were employed for at least one year in nuclear power production facilities or in specialized activities including research, waste management, and production of fuel, isotopes, and weapons.

The current work 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 ionizing radiation.

Existing radiation protection recommendations 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 Japanese survivors of the atomic bombs; extrapolation of risks from this data set to the general population and radiation workers has been controversial.

In the current research, risk estimates per level of radiation dose were calculated for deaths from all cancers excluding leukemia and from leukemia excluding chronic lymphocytic leukemia. 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 percent increased risk of mortality from all cancers excluding leukemia and a 19 percent increased mortality from leukemia excluding chronic lymphocytic leukemia.
On the basis of these estimates, the authors suggest that 1-2 percent of deaths from cancer among workers in this study may be attributable to radiation.

The authors also noted, 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-ray and gamma-ray 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, according to the authors. 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.