The prevalence of shiftwork, a system in which people work in shifts, has increased considerably over the past fifty years in most industrialized countries, and is currently rapidly increasing in the developing countries. This can result in a variety of problems both for the individuals concerned and the organizations employing them. Central to these problems is the fact that we have evolved as a diurnal* species with an internal body clock that sends us to sleep at night. This internal body clock is disrupted when people work at abnormal times, and this disruption is thought to be related to many of the shiftworkers’ problems.
After sleep disturbances, health and wellbeing are undoubtedly the most widely and extensively [31] (1. research 2. researched 3. researching) factors linked to shiftwork. A number of studies have reported increased statistics for affective disorders such as depression, and stomach disorders, especially ulcers. Recent reports have also [32] (1. explained 2. perceived 3. linked) shiftwork with impaired immune function.
As regards the coping strategies, there are a number of possible “interventions” that may help to alleviate the problems associated with shiftwork. The earlier bias towards permanent shift systems – systems which assumed complete adjustment of circadian** rhythms – has now been reversed in Europe to a bias in favor of (rapidly) rotating shift systems that should minimize the disruption of such rhythms. Some researchers also argue that permanent shift systems are probably undesirable, and that rotating shift systems that progressively delay the shift (i.e., in the order: morning → evening → night) result in fewer problems for the individuals concerned than those that progressively advance the shift (night → evening → morning). [33](1.if 2. Since 3.although) the evidence on this latter point is far from conclusive.
Ideally, this [34(]1. choice 2. relationship 3. balance) between rotating systems and permanent systems needs to be considered not only in relation to performance efficiency, but also in relation to medical and social criteria, yet there are insufficient medical data available for any valid comparison to be made. However, it is arguable that the reduced sleep deprivation and undisrupted circadian rhythms associated with rotating systems may make them the lesser of two evils.
Shift workers typically complain of insufficient time for friends, and of [35] (1. missing out 2. catching 3. drawing) on being active members of organizations such as political parties and parent teacher associations. Many also complain that they had to give up some form of hobby or leisure activity and have fewer friends than day workers. Nevertheless, when rotating shift systems have been introduced, they have usually proved highly acceptable, since they allow [36] (1. at least 2. at most 3. at best) some normal social activity every week.
Other important features of shift systems include the timing and duration of shifts, the duration of the rest period between shifts, and the accumulated hours worked [37](1. in the middle of 2 . after 3. before) a rest day. While many researchers in this area agree that there is probably no [38] (1. more 2. far 3. single) ‘best’ shift system for all situations, most would support the move towards placing specific limitations on various features of shift systems.
In the future, a second form of intervention [39](1. may well 2. is about to 3. is willing to) be to try to maximize the adjustment of ‘individuals’ circadian rhythms to their work schedule by the use of appropriately timed administration of bright light or melatonin. Advances in the last decade suggest that this is certainly a possibility and there have been a few experimental trials on real shift workers showing that these manipulations may improve circadian adjustment and reduce sleep problems. [40](1. However 2. Moreover 3. Subsequently), the long-term consequences of adjusting individuals’ circadian rhythms to their shifts and then readjusting them back to normal for their rest days have 41](1. done 2. Yet 3.most) to be determined.
Indeed, a [42] (1. plausible 2. Selected 3. farfetched) explanation for many of the health problems associated with shiftwork is that they stem from exactly the continual adjustment and readjustment of individuals’ rhythms that manipulations such as the use of bright light or melatonin are designed to maximize, [43](1. the fact 2. suggesting 3. on the assumption) that these manipulations may actually exacerbate longer-term health problems. While there is some recent, but indirect, evidence to support this point, there is clearly a need for more research on the potential long-term effects of the use of these manipulations before they can be [44] (1. Recommended 2. Controlled 3. Examined) for widespread use.
A third form of intervention is more concerned with the individual, and is based on individual differences in tolerance to shiftwork, and on the development of appropriate coping strategies. It is obvious that individuals differ substantially from one another [45]（1. Of 2. About 3. In) their ability to tolerate shiftwork, and individual difference measures have met with some success in predicting these differences in a long-term research program. However, they could not readily be used for personnel selection purposes because it would be very easy for candidates to [46]（1. Fake 2. Examine 3. Calculate) desirable scores on them. Nevertheless, they might prove useful in counseling individuals as to whether they would be likely to tolerate shiftwork and, [47] (1. if so 2. in turn 3. as a result), how best to develop adequate coping strategies.
Some researchers have suggested specific coping strategies that should reduce the problems that an individual encounters as a result of shiftwork. These coping strategies are concerned with the scheduling of various activities, such as sleep and meals, which are [48] (1. over 2. beyond 3. under) voluntary control. However, there is only very limited evidence for the efficacy of those coping strategies, and even this may have been [49] (1. confounded 2. explained 3. made explicit) by differences between individuals in whether they had chosen to work on their particular schedule.
Nevertheless, it is clear that sleep taken at a regular time is likely to stabilize circadian rhythms, while an irregular sleeping pattern may disrupt them. 1 Indeed, there is evidence that four hours’ sleep taken during the night, in combination with an additional four hours taken at an irregular time of day, is sufficient to prevent the disruption of most rhythms. In practice, many night workers do take a nighttime nap (often unofficially) although this is seldom [50] (1. of 2. for 3. by) four hours duration. All in all, however, there is a need for further research before proposing the most effective ways for individuals to cope with their shift systems.
Notes
*diurnal: (of animals) active during the day
**circadian: of rhythmic biological cycles recurring at 24hour intervals
***melatonin: a kind of hormone which promotes sleep
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