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Body Clock Disruption, Linked With Travel Across Time Zones, Seen in Study of Flight Attendants

NIOSH Update:

Contact: Fred Blosser (202) 401-3749
October 16, 2003

Female flight attendants are more likely to experience disruptions in circadian rhythm – the body clock—than a comparison group of women who do not frequently fly, and the disruptions are linked with flights across different time zones, a new study by the National Institute for Occupational Safety and Health (NIOSH) suggests.

The study draws no conclusions as to whether the disruptions have long-term health effects. As it was intended to do, it will 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.

The study builds on earlier NIOSH research which found that flight attendants had more sleep disturbance than the comparison group of teachers.

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.”

Dr. Howard added, “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, 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.

Some past studies by other research institutions addressed circadian disruption among small numbers of flight attendants or flight crews on specific flights. The new NIOSH study is the first to address the question on a larger scale among flight attendants flying their normal schedules, for results that can be generalized with greater reliability.

In the new study, NIOSH measured melatonin in daily urine samples, used sensors to monitor sleeping and waking cycles, and gathered information on the flight attendants’ work schedules and routes from individual flight records. The researchers took into account factors other than work schedules that might influence sleeping and waking cycles, such as caffeine consumption, alcohol consumption, and stressful conditions at home and on the job.

The study, “Measuring and Identifying Large-Scale Metrics for Circadian Rhythm Disruption in Female Flight Attendants,” is published in the October 2003 issue of the Scandinavian Journal of Work, Environment, and Health. For further information about NIOSH research, call toll-free 1-800-35-NIOSH(1-800-356-4674).