Prevalence and consequences of sleep disorders in a shift worker population
Introduction
A well-known risk factor for insomnia and excessive daytime sleepiness complaints are working conditions, especially shift work. The rate of sleep complaints in this specific population is higher than rates found in the general population. These problems are mainly due to a disruption of the normal sleep/wake rhythm, of the normal circadian REM sleep rhythm and of the rhythm of REM/non-REM sleep patterns. Thus, the sleep problems of shift workers are partly a circadian one. Several studies have reported that the total sleep duration is related to the body temperature rhythm at bedtime [1], [2], [3]. Studies using a sleep diary of workers as well as laboratory studies have shown that the main sleep period at an unusual time is 1–4 h shorter than night sleep [4], [5]. However, other factors are also involved in the deterioration of sleep quality: fatigue, stress, daylight, health and age.
Whether these disorders are causing more sick leaves in shift workers is unclear: Previous studies have reported contradictory results in this respect. Some found a lower absence rate in shift workers than in day workers [6], [7], while others found higher rates of sick leave and a higher number of visits to work site clinics in shift workers [8].
These contradictory results have lead some researchers [9], [10] to hypothesize that there may be a natural selection process among shift workers: Those having difficulties adapting to shift work usually transfer to day work. The rare studies that have tested this hypothesis tend to confirm it. The results of the Lavie et al.'s study [9] indicated that the occurrence of sleep disturbances appeared to be a good marker of the adjustment level to shift work.
One of the main consequences of having the main sleep period at an unusual time is an excessive sleepiness during wakefulness. This phenomenon is often evoked when attempting to explain human catastrophes occurring at night such as the Chernobyl nuclear accident, airplane crashes and road accidents. Furthermore, decreased vigilance may cause the individual to be more vulnerable to work-related accidents.
We investigated the effects on sleep of three different work schedules among the staff of a psychiatric hospital: fixed daytime schedule, rotating daytime schedule and shift or night working.
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Participants
All staff members of the Vinatier Hospital, a large psychiatric institution located in Bron (France), were invited to participate in the study. There were 2007 staff members at the hospital. Overall, 817 employees volunteered to participate in the study. The distribution of the sample was quite similar to that of the entire staff of the hospital. Administrative staff members were overrepresented in the final sample (Table 1). Medical staff composed the majority of the sample. Employees were
Results
Subjects working on a rotating daytime shift were younger (37.6±8.4 years) than the fixed daytime work group (42±8.3 years) and the fixed or rotating nighttime work group (41.4±6.5 years) (P<.001). There were also more women in the rotating daytime shift group (78.6%) compared with the fixed daytime work group (68.1%) and the fixed or rotating nighttime work group (59.6%) (P<.001).
The interviews were done during the morning shift for 52.6% of the subjects in the rotating daytime shift group;
Discussion
This study was conducted with 817 staff members of a psychiatric hospital. The employees were divided into three groups depending on their work schedule. One group included only daytime workers, a second group was composed of employees who alternated between morning and afternoon shifts and the last group included night workers and workers rotating between day, evening and night shifts. The results show that employees rotating between morning and afternoon shifts had greater sleep difficulties
Acknowledgements
This study was supported by the “Centre Hospitalier Le Vinatier” and by an unrestricted educational grant from Rhone-Poulenc Rorer. We thank Dr. Claude Vieux for her outstanding work in the realization of this study.
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