A French court has for the first time recognised cosmic radiation as a factor in the breast cancer of a long-serving flight attendant.

Sophie Lainault, a 59 year-old former stewardess on Air France, sought to have her cancer recognised as an occupational disease, brought on by conditions at work.

This has now been confirmed in a landmark court ruling in the southwestern town of Bayonne, which said that cosmic radiation was one of three carcinogenic hazards arising from her profession. The other two were passive smoking and prolonged night work.

Smoking was authorised on Air France flights until 2000.

The decision means that Lainault, who is in remission from her cancer, can take early retirement with any further treatment fully reimbursed by the French health system.

And by establishing breast cancer as an officially-recognised risk for flight crews, the court has also cleared the way for many other similar claims, lawyers say.

"My dearest wish is that the decision encourages other women who up until now have not had the courage to take this step," Lainault said.

As stewardess and later purser on Air France airliners, Lainault clocked up 12,600 flight hours between 1989 and 2019. More than half of these were at night.

Many long-distance high-altitude flights from Paris would have taken her near the North Pole, where exposure to radiation from space – strictly speaking particles from the sun and other stars – is the most intense.

A study this month at the Harvard Medical School in the US found that flight attendants and pilots had the highest level of radiation-related cancer deaths among more than 500 different professions.

In all, about 6.9% of deaths among flight attendants and 6.7% of deaths among pilots were from radiation-related cancers, according to the analysis.

These proportions were higher than for other professions including nuclear technologists, who are routinely exposed to radiation from non-cosmic sources yet placed 12th on the list, the authors said.

It has long been known that air travel at high altitudes exposes people to cosmic radiation, but the dose for most travellers is regarded as statistically insignificant. Exposure at the poles is more intense because elsewhere the earth's magnetic field acts as a shield.

"In France the link between breast cancer and certain hazards has been established for a number of professions, such as nurses … but this is the first time for an air-hostess," said Lainault's lawyer Elisabeth Leroux.

Air France said it had played no part in Lainault's legal case and had not seen the reasoning behind the court's decision.

"The health and security of our staff is an absolute imperative," it said. "Every employee has a medical accompaniment that goes well beyond the regulatory minimum."