The study draws no conclusions as to whether the disruptions have long-term health effects. It will be used to guide further NIOSH research for determining if job-related factors place flight attendants at a greater-than-expected risk of reproductive disorders.
The study compared 45 flight attendants with 26 teachers who were similar in age, lifestyle and reproductive history. NIOSH identified disruption in circadian rhythms by measuring variations in levels of melatonin, a hormone that helps regulate the body's sleep-wake cycle.
In people who work during the day and have regular sleep schedules, the body produces melatonin at night with little day-to-day variation. The flight attendants had much greater day-to day variation in melatonin production than the teachers did.
In looking at the statistical values that represented the highest 25 percent of variability in melatonin production, the researchers found that the values were twice as likely to be associated with flight attendants. Among the flight attendants, those with the greatest variations in the production of melatonin were those who most often were on flight schedules that took them across multiple time zones.
"As a rule, disruptions in the body clock can affect the balance of hormones in the body, and this may have implications for reproductive health because hormones play key roles in women's reproductive lives," said NIOSH Director John Howard, M.D. "Given the complexity of those processes, we do not yet know whether the disruptions seen in this study would affect the body in ways that would inhibit or impair reproductive health."
Howard added that in the meantime, the study points up the importance of ongoing NIOSH research in this area, including a pending study that will assess reproductive hormones in flight attendants. "And in an era in which traditional 9-to-5 work schedules are less and less the norm," he said, "it also highlights the importance of research to understand sleep disturbance and fatigue, assess their potential association with unconventional work schedules and assignments, and determine their potential occupational health implications in a wide variety of work settings."
NIOSH is conducting its research on occupational factors and reproductive health in flight attendants at the request of the Federal Aviation Administration and in partnership with flight attendants unions, airlines and other federal agencies. In related studies, NIOSH also is assessing flight attendants' other potential exposures, including cosmic radiation and airborne contaminants in aircraft cabins.