May 12th, 2015 10:56 am ET - Barbara Grajewski, PhD
Some job hazards for flight attendants have changed greatly over the years. For example, while U.S. flight attendants are no longer exposed to second hand smoke at work, today there are heightened safety concerns due to terrorism , but some hazards have been present on the job since the first flight attendants started working. Flight attendants often travel across time zones, working when others normally sleep, and are exposed tocosmic radiation from the sun and space. A NIOSH study published earlier this yearexamined the risks of cosmic radiation, circadian disruption (from working during normal sleep hours), and other work exposures on pregnancy outcomes for flight attendants.
Our study looked at individual flight segments for each flight attendant in the study. We studied 958 pregnancies among 764 female flight attendants from three U.S. airlines over 4 years. To assess each woman’s exposure to cosmic radiation and circadian disruption, we reviewed company records of over 2 million flights flown by the flight attendants in the study. We also assessed other exposures including physical job stressors by questionnaire.
Our study is the first to assign two estimated radiation doses to each specific flight: one dose from ever-present galactic cosmic radiation, and one dose from a solar particle event if one occurred during that flight.
Solar particle events, also known as “solar flares,” are eruptions of radiation from the surface of the sun which can increase radiation levels on earth and in aircraft. The solar particle event estimates were based on individual flight records and NASA’s Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS) model. Flight attendants in our study did not fly through a solar particle event very often. However, radiation exposure from flying during some solar particle events could result in a radiation dose that exceeds national and international recommended limits for pregnant workers.
Looking at both galactic cosmic radiation and solar particle event radiation doses together, our study suggests that cosmic radiation exposure of 0.1 milligray (mGy) or more may be associated with a 70% increased risk of miscarriage for flight attendants in the first trimester, compared to similar pregnant flight attendants whose flights exposed them to less than 0.1 mGy of radiation in first trimester. This research finding suggests that the much higher threshold of 50 mGy for adverse reproductive outcomes reported in earlier studies of atomic bomb survivors should be re-examined. All radiation dose estimates have some degree of uncertainty and additional studies will be needed to confirm these findings.
Circadian Disruption and Physical Demands
Body functions can be disrupted by changes in sleep patterns, which in turn affect the body’s biological clock. These changes are called “circadian disruption”. Aircrew may experience jet lag, a type of circadian disruption, as they work.
We used airline records to estimate each flight attendant’s cumulative sleep disturbance during their first trimester of pregnancy. We added up the time the flight attendants were working in the air when they would normally be asleep at home and also looked at travel through multiple time zones. Miscarriage in the first trimester was 50% more likely for a pregnant flight attendant who flew 15 hours or more during her normal sleep hours (that is, during her sleep hours at her home base), compared to those who flew less during normal sleep hours. This finding is consistent with several other studies that have examined the association between shiftwork and adverse reproductive health outcomes.
Among several kinds of physical job stressors, we found that standing and walking for more than 8 hours a day and bending at the waist more than 25 times a day were risk factors for miscarriage. We found that miscarriage in the first trimester was about 2 and a half times as likely for a pregnant flight attendant with high physical job demands compared to pregnant flight attendants with low physical job demands. This finding is consistent with several other studies that have examined the association between physical job stressors and adverse reproductive health outcomes.
What Should be Done About it?
National and international airlines, flight crew unions, regulatory agencies and other stakeholders need to revisit regulations, guidelines, and training for best work practices for pregnant aircrew members to reduce risk of adverse reproductive health outcomes. This research and prevention may also apply to other pregnant workers exposed to shift work, physical job stressors, and radiation.
Visit the NIOSH Update page on our study or the Aircrew Safety and Health topic page for more information.
Barbara Grajewski, PhD
Dr. Grajewski is a senior epidemiologist in the NIOSH Division of Surveillance, Hazard Evaluations, and Field Studies.