Working Partnerships: Applying Research to Practice, NORA Symposium 2003, Washington, DC: National Institute for Occupational Safety and Health, 2003 Jun; :126
America is a nation of tired workers. In 1990, the direct U.S. costs of sleep disorders and deprivation were estimated at $15.9 billion, and the indirect costs which result in stress-related, reduced workplace productivity were estimated at $150 billion. Air travel during normal sleep hours and multiple time zone changes are an integral part of the workplace for many of the 198,000 air crewmembers employed in the United States, including about 113,700 flight attendants. Flight attendant sleep cycle/circadian rhythm disruption issues may in some ways be similar to those of shift workers, but a flight attendant’s work schedule often lacks the regularity which assists a shift worker’s circadian resynchronization; also, a flight attendant’s work often involves rapid movement through multiple time zones, and the resultant disruption of zeitgeibers (external time cues) is different than for shift workers. Because circadian disruption may affect the hormonal balance requisite to reproductive health, it is being assessed among flight attendants in reproductive health studies which The National Institute for Occupational Safety and Health (NIOSH) is currently conducting. Our objectives were to determine whether female flight attendants are more likely than teachers (comparison group) to experience circadian disruption, as measured by melatonin production and sleep displacement, and to identify metrics of disruption for future studies of reproductive health. Each day for one menstrual cycle, 45 flight attendants and 26 teachers kept a daily diary, collected and measured their overnight urine, and wore an activity monitor to assess sleep displacement. Relations between melatonin production, sleep parameters, and flight attendant/teacher status were analyzed with linear and multiple logistic regression. Relations between sleep displacement, melatonin, and flight history-derived variables (including time zones crossed) were examined with exploratory factor analyses. Flight attendants experienced increased circadian disruption as measured by a higher adjusted melatonin rate variance than teachers (2.8 x 105 vs. 1.0 x 105 (ng/h)2 , respectively; p=0.04) and the likelihood of being in the highest quartile of melatonin variance (Odds Ratio = 2.3; 95% Confidence Interval: 0.6 - 9.1). Although flight attendants slept longer than teachers, models for two indices of sleep displacement indicated that flight attendants incurred significant impairment of sleep compared to teachers. In factor analysis, time zones crossed was related to both melatonin desynchronization and sleep displacement. Flight attendants experienced increased circadian disruption, as measured by more variable melatonin rates and increased sleep displacement, than a minimally-flying comparison group. For epidemiologic studies of flight crew in which melatonin measurement is infeasible, time zones crossed is a useful indicator of both sleep displacement and melatonin desynchronization. Rest requirements for flight attendants may address issues such as alertness, but misalignment of the sleep-wake cycle and circadian rhythms may be a chronic occupational condition which may not be readjusted fully by rest after each duty period. Although worker alertness is a key safety issue in many industries, sleep and circadian rhythm research need to be expanded to determine chronic health effects of sleep impairment and, for air crew, circadian disruption.