A new NIOSH study, "Measuring and Identifying Large-Scale Metrics for Circadian Rhythm Disruption in Female Flight Attendants," finds female flight attendants more likely to experience disruptions in circadian rhythm — the body clock — than a comparison group.

The study compared melatonin levels, sleep and wake cycles, and work schedules of 45 flight attendants with 26 teachers. Results show that the flight attendants had much greater day-to-day variation in melatonin production than the teachers.

NIOSH says the findings will help guide research to determine if such effects signal long-term risk for adverse reproductive effects.