U.S. flight attendants experience a higher risk of several forms of cancer, leading researchers to call for more study on how to minimize the occupational exposures and conditions they suspect are contributing to the disparity.

In analyzing data from the Harvard Flight Attendant Health Study, which includes more than 5,300 participants, researchers found that flight attendants have a higher prevalence of multiple cancers, including breast cancer, uterine cancer, gastrointestinal cancer, thyroid cancer and cervical cancer. The study is now one of the largest and most comprehensive investigations into cancer among flight attendants to date and is also the first to show that such workers experience higher rates of nonmelanoma skin cancer than their peers in the general population.

The study, published this week in Environmental Health, compared flight attendants’ self-reported data to data from Americans with similar socioeconomic statuses who participated in the National Health and Nutrition Examination Survey.

“Our findings of higher rates of several cancers among flight attendants is striking given the low rates of overweight and smoking in our study population, which highlights the question of what can be done to minimize the adverse exposures and cancers common among cabin crew,” said study co-author Irina Mordukhovich, a research fellow at the Harvard T.H. Chan School of Public Health, in a news release.

In particular, the study found that of the more than 5,300 flight attendants in the study, just more than 15 percent had ever been diagnosed with cancer. Breast cancer prevalence among flight attendants was 3.4 percent versus 2.3 percent in the general population; prevalence of uterine cancer was .15 percent versus .13 percent; cervical cancer prevalence was 1 percent, compared to .7 percent; gastrointestinal cancer was at .47 percent, compared to .27 percent; and thyroid cancer was at .67 percent among flight attendants versus .56 percent in the general population.

Job tenure didn’t appear to be associated with breast cancer, melanoma or thyroid cancer in all women, but the study did detect a higher risk of breast cancer in women who didn’t have children and among those with three or more children. Researchers also found an association between every five-year increase in working as a flight attendant and nonmelanoma skin cancer among women. Male flight attendants experienced higher rates of melanoma and nonmelanoma skin cancer than their counterparts in the general population, especially if they were exposed to high levels of secondhand smoke in the days before airlines banned smoking.

Researchers said their findings were consistent with workplace exposures that flight attendants commonly face, such as ionizing radiation, poor indoor air quality, chemical carcinogens such as flame retardants and jet fuel, and historical exposures to secondhand cigarette smoke. In fact, the study noted that cabin crew workers experience the largest annual dose of ionizing radiation of all U.S. workers. Another possible contributor was circadian rhythm disruption — or a person’s sleep-wake cycle — which is a factor many researchers believe may similarly affect cancer risk among night shift workers.

The study points out that U.S. cabin crew workers benefit from fewer workplace protections than most other workers — in fact, flight attendants were excluded from U.S. Occupational Safety and Health Administration safeguards until 2014, when limited protections were put into place. In comparison, flight attendants in the European Union enjoy a range of protections, such as requirements that airlines monitor radiation doses, implement scheduling practices that limit such exposures and inform workers about occupational risks.

“Our results yield information to guide future research regarding the health of this understudied group of workers, which can also be considered when evaluating how to improve health and quality of life among cabin crew,” the study concludes.

For a full copy of the study, visit Environmental Health.