Flight attendants may face higher than average risks of breast and skin cancers, a new study finds, though the reasons why aren't yet clear.
Harvard researchers found that compared with women in the general US population, female flight attendants had a 51% higher rate of breast cancer. Meanwhile, their rates of melanoma and non-melanoma skin cancers were about two to four times higher, respectively.
The ongoing Harvard study which began in 2007 and included over 5 300 US flight attendants, is not the first to find heightened cancer risks among airline crews.
But it's one of the largest and most comprehensive to look at the issue, according to lead researcher Eileen McNeely. However, because it's what's called an observational study, it could not prove cause and effect.
Contact with a number of chemicals
Flight crews have a number of exposures that could potentially play a role, said McNeely, an instructor in environmental health at the Harvard School of Public Health. "There's been a lot of speculation about exposure to cosmic ionizing radiation," she said.
That refers to radiation that comes from outer space. At flight altitudes, people are exposed to higher levels of it. The US National Institute for Occupational Safety and Health (NIOSH) says that of all US workers exposed to radiation, aircrew have the highest average levels.
But no one knows for sure whether cosmic radiation is to blame for flight attendants' higher cancer risks, McNeely said. Aircrews can also come in contact with a number of chemicals, she noted. And before smoking bans went into effect, they were habitually breathing in secondhand smoke.
Plus, McNeely said, flight crews deal with constant time-zone changes and irregular sleep schedules, which means many disruptions to the body's circadian rhythm, or "internal clock".
"It's hard to tease out which of those factors might be more important than others, or whether it's a combination of all of them," McNeely said. However, it's also possible that there are factors unrelated to flight attendants' jobs, said Dr Paolo Boffetta, a professor of oncology and environmental medicine at Mount Sinai's Icahn School of Medicine, in New York City.
"For example, they may have more UV [sun] exposure because of their opportunity to travel," said Dr Boffetta, who was not involved in the study.