Prevalence and consequences of sleep disorders in a shift worker population

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Abstract

Introduction: Irregular work schedules often results in a disruption of the normal circadian rhythm that can causes sleepiness when wakefulness is required and insomnia during the main sleep episode. Method: Two physicians using the Sleep-EVAL system interviewed 817 staff members of a psychiatric hospital. The interviews were done during the working hours. In addition to a series of questions to evaluate sleep and mental disorders, the evaluation included a standard questionnaire assessing work conditions, work schedule and their consequences. Three work schedules were assessed: (1) fixed daytime schedule (n=442), (2) rotating daytime shifts (n=323) and (3) shift or nighttime work (n=52). Results: Subjects working on rotating daytime shifts were younger than the two other groups and had a higher proportion of women. Participants working on rotating daytime shifts reported more frequently than the fixed daytime schedule workers to have difficulty initiating sleep (20.1% vs. 12.0%). The sleep duration of shift or nighttime workers was shorter than that of the two other groups. Furthermore, subjects working rotating daytime schedule reported to have shorter sleep duration of about 20 min when they are assigned to the morning shift. Work-related accidents were two times more frequent among the rotating daytime workers (19.5%) compared with the fixed daytime schedule workers (8.8%) and the group of nighttime or shift workers (9.6%). Sick leaves in the previous 12 months were also more frequently reported in the rotating daytime schedule group (62.8%) as compared with the daytime group (38.5%, P<.001); 51.9% of nighttime or shift workers took sick leave. Conclusions: Working on a rotating daytime shifts causes significant sleep disturbances. As consequences, these workers are more likely to feel sleepy at work and are more likely to have work-related accidents and sick leaves.

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.

Section snippets

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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