A study of more than 5,000 US flight attendants has shown they have higher rates of certain cancers than the general public.

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And it was only associated with higher risk of breast cancer in women who either had never had children - nulliparity - or had three or more.

The prevalence of breast, melanoma and non-melanoma cancers were especially striking, says Mordukhovich.

"Having fewer children and having children later in life are known risk factors for breast cancer", Pinkerton, who wasn't involved in the current study, said by email.

While these results confirm earlier research linking work as a flight attendant to an increased risk of certain cancers - especially breast and skin malignancies - the study wasn't created to prove whether or how the job might directly cause tumors. The new study, published Monday in the journal Environmental Health, saw the same trend and detected a higher prevalence of every other cancer the researchers examined: Non-melanoma skin cancer, uterine, gastrointestinal, cervical and thyroid cancers were all seen at a higher rate in flight attendants.

At high altitudes, where the air is thinner and provides less of a shield, passengers and crew can be exposed to between 100 and 300 times the cosmic radiation dose they receive at sea level.

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This is because they fly more northerly routes where exposure to cosmic radiation is highest. That exposure may not be concerning for people taking individual flights, but for people whose jobs involve flying, that risk may have a negative effect on their health, as the study results suggest.

The National Institute for Occupational Safety and Health (NIOSH) lists circadian disruption and cosmic radiation as potential cancer causes.

The National Council on Radiation Protection and Measurements reports that flight crews are exposed to the largest annual dose of radiation among US radiation workers. 30 flight hours of exposure to ionizing radiation would equal one chest x-ray, but they spend much less time in the air than a flight crew.

How can cancer risks be minimized in flight attendants?

The authors used self-reported data from 5,366 USA flight attendants and compared it with data from a matching group of 2,729 men and women with similar economic status who participated in the National Health and Nutrition Examination survey collected during the same years.

Irina Mordukhovich, corresponding author of the study, said the research is one of "the largest and most comprehensive studies of cancer among cabin crew to date". Researchers said the findings are particularly worrying considering the relative good health of the flight attendants included in the tests.

Dr. Mordukhovich knows of no studies about cancer risk in frequent fliers, but they are at risk of being exposed to ionizing radiation and possible shifts in their sleep-wake cycles. "We hope the study highlights issues about exposures that we know are problematic for flight attendants and pilots and aren't now being addressed".