Preliminary studies suggest that air hostesses are almost twice as likely to suffer breast cancer and 15 times more likely to have bone cancer than women in the general population. Pilots appear to have the highest leukaemia risk of any occupation, and are more likely to develop melanoma and cancer of the lower gut, according to a study in the journal, Aviation Space and Environmental Medicine.
The studies involved small numbers of people, and researchers have stressed that more research is needed to substantiate or refute the findings. But they also raise questions over the type of radiation the crew are exposed to, and whether this has been taken into account when calculating risk.
Airlines have repeatedly played down the dangers of cosmic radiation exposure to avoid alarming crew and passengers who fly regularly, although a large American survey is underway to establish if there is any risk to frequent flyers.
The airlines have failed to reassure some pilots, including British pilots, who now carry personal radiation monitors on the flight deck. The British Airline Pilots Association is funding a study by scientists at Bremen University to assess chromosome damage to Concorde crew who, because they fly at higher altitudes (about 59,000ft), are exposed to the highest levels of radiation.
Balpa plans a second study for pilots on subsonic flights flying regularly at 39,000ft, and is recruiting volunteers to carry monitors with them when they fly. Carolyn Evans, technical secretary for Balpa, said: "It is something we are greatly concerned about. We are fortunate in that excellent data exists for Concorde crews because it was required by law to carry monitoring equipment."
The EC directive, which comes into effect in May 2000, runs contrary to the airline industry's repeated dismissal of the dangers of cosmic radiation exposure, and their attempts to discredit any research which indicates otherwise.
A decision to include air crew in the directive, which lays down safety standards for the protection of workers and the general public from radiation, follows a study by Finnish scientists published in the British Medical Journal last year. This study, the first of its kind, assessed the cancer risk of all cabin crew who had ever worked on Finnish airlines and who had not died before 1 January 1967 - a total of 187 men and 1577 women.
Dr Eero Pukkala of the Finnish Cancer Registry, and Anssi Auvinen of the Finnish Centre for Radiation Nuclear Safety, found "significantly raised risks" of breast and bone cancer in air hostesses. A second study by the Danish Cancer Society found an excess of breast and bone cancers and leukaemias among cockpit and cabin crew.
A study for the German Cockpit Association found that pilots were up to 10 times more likely to have chromosome abnormalities than the general population, although the significance of the abnormalities is not known.
Cosmic radiation originates in outer-space and radioactive particles are drawn towards the North and South Poles by magnetic forces. Airline crews are chronically exposed to cosmic radiation, mainly from neutrons and gamma rays. The mean annual dose is estimated at between 1000-3000 microSieverts (a unit of radiation) per year but this varies according to flight altitude - the dose doubles every 4,920ft - latitude, and solar activity.
According to the National Radiological Protection Board which is responsible for the safety of aircrew, the limit of exposure is 6000 microSv in any one year. The average radiation dose experienced by crew flying at 39,000ft is 5 microSv per hour, and 10 microSv for supersonic flights.
Dr Chris Sharp, head of the Medical Department at the NRPB, said that even on the "worst case" radiation exposure, the London to Tokyo route, crews will accumulate 5400 microSv, well below the NRPB recommendation. Exposure on the ground of the general population is about 2200 microSv per year, and an X-ray delivers a dose of 20 microSv.
Dr Michael Bagshaw, head of Aviation Medical Services at British Airways, said that the risks to crew posed by cosmic radiation was minimal, and that a study of pilots flying between 1966-1989 showed that they had seven more years life expectancy than a similar population of non-flyers. He said 21 years of data from Concorde flights did not show any increased risk of cancer.
"There have been commercial flights for more than 50 years and no evidence of an excess of cancers. The international limits for occupational [radiation] exposure is 20,000microSv per year or 100,000microSv in five years with up to 50,000 in anyone year. Crew are well within that. We would be foolish to say there is no risk but we are confident that it is minimal," Dr Bagshaw said.
Additional research Amelia Hill