LONDON, Jan 18 PA - People who fly frequently were warned today that they could face a serious risk of cancer.The danger was underlined by new research indicating high rates of breast and skin cancers among air crews.

A study of almost 6000 flight attendants showed that their chance of suffering breast cancer was 30 per cent higher than average. They also had double the normal risk of skin cancer.Previous research has shown heightened rates of a wide range of cancers among air crews, including leukaemia, prostate, skin, bowel and brain.But in most cases the increases have been slight. The new study from California is the largest of its kind ever undertaken, and shows a big effect.

The cause is cosmic radiation which floods high-flying aircraft, according to experts.With every 2166m of altitude, an individual's exposure to cosmic radiation from space doubles. Four hours spent in the air at 10,000 metres is equivalent to undergoing one chest X-ray.Much of the radiation comes from the sun, and is greatly increased by high levels of solar activity. Solar flares can increase radiation exposure by up to 20 times - and right now the sun is near the peak of its 11-year activity cycle. The risk is especially pronounced when flying over the poles.

Farrol Kahn, director of the Aviation Health Institute, a charity which investigates the health risks of flying, said people should take the invisible threat seriously.He said of the new findings: "This is a large study of 6000 people, which is pretty positive evidence. It sends out a warning to frequent flyers, especially female business executives, that they need to be aware of the danger.""The more you are exposed, over say 10 or 20 years, the higher the dosage you will receive and the greater the risk of cancer. "We think the EU should consider issuing a directive requiring employers to issue advisory circulars about the radiation risk from flying to their staff." Such a directive already applied to air crews.

Mr Kahn warned that pregnant women needed to take extra care, because it was possible their babies could be harmed."During the first three months of pregnancy radiation can have harmful effects on the foetus," he added. "Any small amount of radiation can cause genetic defects."

The findings from the California Department of Health Services are due to be published next month but were reported today by Sky Television.

The study matched members of the US Association of Flight Attendants against California's state cancer registry.It found 175 cases of newly-diagnosed cancer between 1988 and 1995, 149 women and 26 men.Breast cancer incidence was more than 30 per cent higher than expected among the general population and melanoma (skin cancer) incidence roughly double. The report concludes: "In summary, this study provides strong evidence that while the overall cancer experience of flight attendants does not differ from that of the general population, they do experience higher rates of certain cancers, particular female breast cancer and malignant melanoma of the skin."

Scientists know from studies carried out after the Atom bomb was dropped on Hiroshima that the kind of radiation which bombards the Earth from space can damage DNA in cells.Normally people are protected from cosmic rays by the Earth's atmosphere, but that protection diminishes rapidly with increasing altitude.

Mr Kahn said the antioxidant properties of vitamin C and E supplements, taken after a long flight, can help reduce the effects of radiation.A glass or two of red wine, which also contains antioxidants, may also be of benefit. But the only really effective way to lessen the risk was not to fly too often.

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