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FORUM on Corrections Research
Shift Work and Its Impact on Human Performance
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Research has shown that three major factors influence an individual's state of alertness and ability to
perform on the job: the circadian cycle (i.e., the body's daily rhythm), sleep disorders and sleep loss.
With shift work, disruption of the circadian system plays major role and may affect a person's
performance at work as well as in family and personal life. This article summarizes information in Lydia Dotto's book, Asleep in the Fast Lane: The Impact of Sleep on Work, one section of which discusses research on shift work. Sleep researchers estimate that about one fifth to one quarter of all workers in the industrialized world work shifts. These people are most likely to be working in protective, food or health services. It is just recently that people have begun to realize that shift-work schedules introduced without regard to the realities of human physiology have many hidden costs, including worker dissatisfaction, health problems, absenteeism, excessive overtime, low morale and family and marital difficulties. The major problem with shift work is that it scrambles circadian rhythms - namely the sleep/wake cycle. Two of the most damaging features of shift work are weekly rotation and phase advancement, that is, shift rotation in a counterclockwise direction from day shift, to night shift, to evening shift. Rotation of shifts on a weekly basis is extremely disruptive. Because it takes the circadian sleep/wake system a minimum of several days to adjust to an eight-hour schedule change, it barely gets a chance to settle down before another change is forced on it. Usually, workers only get two or three days off between shift changes, during which time they often go back to a normal sleep/wake pattern that further disrupts the circadian system. An added complication is the large time shifts involved. The circadian system can readily adjust to a change of an hour or two a day, but a sudden eight-hour shift produces about as much circadian disturbance as flying from the middle of North America to Europe. Added to this is the problem that shifts often rotate counterclockwise, creating a phase-advance situation. This works against the natural tendency of the human circadian system toward phase delay. More than 60% of people who work shifts complain of sleep disturbances, compared with about 20% of regular day workers. Problems with insomnia, chronic fatigue and sleepiness on the job are common problems, particularly for people working on night shifts. When workers first begin a night shift after being on days, they usually have trouble staying awake in the middle of the night, during what is called the circadian "trough." This is when their biological clock says it is time to go to sleep. In the morning, night workers have the opposite problem: it is time for them to go to bed, but their circadian system is reaching its daytime peak alertness. Studies indicate that most shift workers average only about five-to-six hours of sleep during the day, unless they stay on their shifts longer than a week at a time. Moving from an evening shift to a day shift also causes trouble for the circadian system. Evening workers are still awake at the time when most day workers normally go to sleep, at about 10:00 or 11:00p.m. They then go to bed later, about 2:00 or 3:00 a.m., and wake up later (about mid-morning) than regular day workers. But when they start a day shift, they must suddenly advance their sleep period to 11:00 p.m. and get up at 7:00 a.m. This is very difficult. It has been equated with asking someone who works regular work days to go to sleep at 8:00 p.m. Of all shifts, afternoons or evenings are perhaps the best for the circadian system, but workers often do not like them because they usually disrupt family and social life. Another major health consequence of shift work is increased digestive problems, particularly among night workers who eat at a time when the circadian system has turned off the digestive juices for the night. Mismatches between the circadian cycle and the external world are most severe during the first few days on a new shift schedule because biological clocks are still set to the old schedule. Weekly rotation, especially in the counterclockwise direction, makes it virtually impossible for the circadian system ever to synchronize properly with the external world. The result is that shift workers often do not get enough sleep. One study found that only 15% of shift workers, compared to 50% of regular day workers, got seven-to-eight hours of sleep per night. Furthermore, the sleep shift workers do get is often not restful. Because many shift workers are chronically sleep deprived, they experience even greater levels of sleepiness at work than would be expected from circadian factors alone. One study compared episodes of falling asleep at work among 907 workers at eight industrial plants, seven of which had shift schedules and one of which operated on straight days. The study found that, on average, more than half of the shift workers reported falling asleep on the night shift and about one fifth reported falling asleep on the day and evening shifts. These figures compare with only 8% of permanent day workers who reported falling asleep at work. Thus, it appears that poor adaptation of the circadian system to rotating schedules causes excessive sleepiness on all shifts, but particularly the night shift. Studies have shown that during the circadian trough between 3:00 a.m. and 6:00 a.m., people make more errors in reading gas meters and responding to warning alarms and take more time to answer telephone calls. A number of sleep researchers have recommended very strongly that shift workers should not be required to work more than three consecutive nights. Increasing automation in many organizations is compounding the problem caused by on-the-job sleepiness. Instead of actually doing things and moving around, many shift workers spend their time watching computers, dials or television monitors. Individuals may vary in their ability to cope with the problems caused by shift work. Younger people, for example, are more adaptable to unusual or irregular sleep/wake schedules than middle-aged or older people. There is also some evidence to suggest that night hawks, who follow flexible sleeping habits, may be more suited to shift work than morning people, who require a more rigid sleep/wake routine. The following are some suggestions to help you adjust to shift work:
L. Dotto, Asleep in the Fast Lane: The Impact of Sleep on Work. (Toronto: Stoddart Publishing, 1990). |
