Original ArticleInsomnia in shift work
Introduction
Shift work is highly prevalent in industrialized societies, representing about 30% of the Canadian workforce [1]. This work schedule characterizes a wide variety of professions such as police officers, truck drivers, air traffic controllers, airline pilots, nuclear power plant operators, and nurses [2]. These professionals expose themselves and their society to significant risks that endanger human lives, as they are more likely to experience sleepiness and reduced alertness that negatively affect their work performance [3], [4], [5]. It is estimated that about 32% of night workers [6], [7], [8], 10% of day workers [8], and 8–26% of rotating shift workers [6] suffer from shift work disorder (SWD). The International Classification of Sleep Disorders-II (ICSD-II) [9] defines SWD as the presence of insomnia and/or excessive sleepiness temporally associated with a habitual work schedule that overlaps usual sleep time. Both insomnia and excessive sleepiness are likely to occur among night shift workers and to interfere with their quality of life. These sleep difficulties are closely related to the sleep regulation system, and are explained mainly by the fact that the work schedule is out of phase with, and often in direct opposition to, the endogenous circadian rhythms [10], [11].
Several negative consequences attributed to shift work schedules have been reported for workers, their employers, and society in general. Many studies on shift work populations have shown that shift and permanent night work may cause various problems for employees [12], [13], [14], [15]. For instance, physical and mental health can be severely affected by stress and sleep deprivation [14]. Knutsson [13] reported that night work is strongly linked to disorders such as gastrointestinal and cardiovascular diseases, diabetes and metabolic disturbances, cancer, and complications in pregnancy. Other studies [12], [15] have associated night work with a higher risk of developing breast and endometrial cancers, because exposure to light at night suppresses melatonin biosynthesis and deregulates circadian genes involved in cancer-related pathways [16]. Shift workers can experience difficulties in falling asleep, and report diminished sleep time and sleepiness during work hours [3], [17]. Night workers often complain of family and social difficulties, as they are out of phase with activities that follow the diurnal rhythm of the general population [4], [18]. Shift work seems to increase the risk of marital separations by 7–11% [19]. Further difficulties appear within the workplace: shift workers show chronic fatigue and anxiety that lead to work dissatisfaction [20]. Both productivity and safety may also be compromised, especially over successive night shifts [21]. These results all show that the negative consequences of shift work are far-reaching and widespread.
It is unclear whether shift work per se explains the consequences attributed to the work schedule, or whether they are the result of SWD. Most authors consider that the sleep difficulties are simply part of the overall negative consequences attributed to shift work. However, it is also well documented that sleep disorders such as insomnia have specific consequences that are independent of the context in which they appear. In the context of shift work, therefore, it may not be easy to parcel out the contributions of shift work per se and SWD (including insomnia), as these variables can be expected to produce similar symptoms, such as depression and anxiety [22], higher risk of motor vehicle accidents [4], work absenteeism, impaired work performance, and increased risk of work-related accidents [23], [24], [25], [26]. Insomnia might also aggravate symptoms associated with the work schedule.
Some studies have attempted to more clearly identify the impact of SWD on the health of shift workers [4], [6], [7], [8], [27], [28], [29]. Workers with SWD seem to maintain a circadian phase similar to that of day workers [29]. SWD was shown to be related to an increased risk of depression, sleepiness, hypertension, anxiety, absenteeism, and road accidents, as well as decreased work performance. Workers with SWD also showed a severely impaired quality of life [7], [8], [28]. Which of these negative consequences of SWD can be attributed to the insomnia symptoms included in SWD? In order to tease out the negative impact of insomnia symptoms on shift workers, a two-by-two comparison needs to be made: shift workers with or without insomnia versus day workers with or without insomnia. Several studies have compared shift workers with day workers [6], [7], [8], [11], [27], [30], [31], [32] but only two seem to have distinguished day workers according to presence or absence of insomnia [6], [11]. In one of these studies [11], the authors concluded that shift workers without SWD are similar to day workers. The other study showed that rotating shift workers with both insomnia and sleepiness had more absenteeism, whereas rotating shift workers with only insomnia were absent more from family and social activities [6]. It would appear that the negative consequences attributed to shift work may be confounded with those related more specifically to insomnia.
The present study specifically addresses the negative impacts of insomnia on the perceived physical and psychological health of shift workers by comparing them to day workers. Second, the study investigates the impact of insomnia on the quality of life, work, and lifestyle habits of shift workers.
Section snippets
Study context
Data analyzed in this study were derived from a larger epidemiological study conducted in Canada. The goals of the original study were to estimate the prevalence of insomnia symptoms and insomnia syndrome in the general population, and to describe the types of consultation initiated for insomnia and products and strategies used to promote sleep. Furthermore, the initial study aimed at evaluating incidence rate and risk factor for insomnia. The first step was a telephone survey to document the
Sleep measures according to work schedule and sleep status
Table 2 shows the means and standard deviations for sleep variables according to work schedule and sleep status. Across work schedule groups, there were significant differences in sleep quality only. Night and rotating shift workers had poorer sleep quality than day workers [F(2, 412) = 6.24, P = 0.029]. In addition, night workers had a nearly significant (P = 0.06) tendency towards higher pre-sleep arousal and to take longer to fall asleep (P = 0.08). Apart from sleep quality, most
Discussion
The present study investigates the impact of insomnia on the perceived physical and psychological health of shift workers. The results suggest that insomnia has similar effects on night, day, and rotating shift workers despite the presence of sleepiness. All three groups present similar profiles, complaining of symptoms of anxiety, depression, and fatigue, and consuming equal amounts of sleep-aiding medication. Insomnia seems also to contribute to chronic pain and ORL problems, especially for
Conflicts of interest
Aida Azaiez, Vincent Moreau, and Mélanie LeBlanc have no conflict of interest, off-label, investigational use, or financial support to disclose. Annie Vallières has a grant from the Canadian Institutes of Health Research (#191771) but it is not related to the present manuscript. Charles Morin has served on consulting/advisory boards for Novartis, Valeant, Merck, and Purdue and received research grant from Merck. However, these are not related to the present study.
The ICMJE Uniform Disclosure
Funding
This research was supported by Canadian Institutes of Health Research grant #42504 awarded to C.M. Morin.
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