Aviation officials say passengers and aeroplane crews should not be overly concerned about negative health effects caused by exposure to cosmic radiation during trans-polar flights as people would have to make more than 200 such flights a year to absorb enough radiation to be affected.

The comments follow the recent launch of China Eastern Airlines' trans-polar Shanghai-New York route.

The atmosphere is thinner in polar regions than at the equator, so more radiation finds its way to earth at the poles.

Medical experts said people who fly over polar areas absorb more cosmic radiation than normal and should take measures to protect themselves, like eating more vitamins.

However, they added that the amount of radiation is within the limits of what is considered safe.

The Shanghai-New York flight lasts 14 hours, reducing flight times by 6 hours compared with transit flights that avoid polar areas.

Insiders said airline companies are increasingly turning to polar routes because of the decreased chance of turbulence and shorter flight times of such routes.

Still, frequent fliers and members of the flight crews that work on polar routes have expressed their apprehension about being exposed to cosmic radiation.

"People are exposed to cosmic radiation during polar flights. The amount a pilot receives each time he crosses a polar area is equal to more than four times what a patient receives while having the X-ray," said Ge Shengqiu, a researcher at the Medical Research Institute of the General Administration of Civil Aviation of China (GACA).

Ge said a pilot absorbs about 0.093 millisieverts (mSV) of radiation during each trans-polar flight, compared with the 0.02 mSV a person absorbs during an X-ray.

Ge said it is almost impossible for passengers on trans-polar flights to absorb enough radiation to cause health problems.

Li Zhe, the division chief for flight standards at GACA, echoed Ge's comments, noting that trans-polar flights would not harm the health of the pilots, flight attendants or passengers.

The International Commission on Radiological Protection has capped the amount of radiation a person can absorb over the course of a year at 20 mSV.

Ge said that if a person absorbed 0.093 mSV of radiation during each trans-polar flight, he would have to make 215 such flights in a year to reach the recommended limit.

In response to widespread radiation concerns, many international airlines seek to avoid the effects of radiation by limiting the number of trans-polar flights their crews make each year.

China Eastern Airline's flight attendants generally work only one trans-polar flight per every two months, said an employee of the company.

The employee added that 500 flight attendants had obtained American visas to work on such flights. Each flight requires 14 attendants, and there are four such flights each week.

These numbers ensure that no attendants will come close to the radiation limit.

Ge said pregnant air hostesses should be aware of cosmic radiation.

"However, usually air hostesses switch to ground services after they become pregnant," he added.

Ge said people could take precautious measures by eating more fruits and vegetables, particularly those rich in vitamins A and C.