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 Table of Contents  
Year : 2020  |  Volume : 37  |  Issue : 4  |  Page : 183-189

Sleep disorders in a shift worker population sample in Turkey

1 Department of Neurology, Faculty of Medicine, Erciyes University, Kayseri, Turkey
2 Department of Biostatistics and Medical Informatics, Çukurova University, Adana, Turkey
3 Department of Neurology, Faculty of Medicine, Çukurova University, Adana, Turkey

Date of Submission31-Mar-2020
Date of Decision06-May-2020
Date of Acceptance31-May-2020
Date of Web Publication29-Dec-2020

Correspondence Address:
Duygu Kurt Gok
Department of Neurology, Faculty of Medicine, Erciyes University, Kayseri
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/NSN.NSN_29_20

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Aims: This study aims to determine the sleep quality of night-shift workers, determine the prevalence and characteristics of sleep disorders related to shift work, and compare sleep characteristics between shift workers and day workers. Subjects and Methods: The study included 1473 individuals employed in three different areas (health, security, and labor) as shift (78.5%) or day (21.5%) workers in the city of Adana, Turkey. Data were collected using a structured questionnaire consisting of 132 questions. The questionnaire included demographic data, education level, socioeconomic status, shift schedule, accompanying health problems, sleep disorders and sleeping habits, the Epworth Sleepiness Scale, the Pittsburgh Sleep Quality Index, the Berlin Questionnaire, and the Restless Legs Syndrome (RLS) scale. Statistical Analysis Used: The SPSS for Windows 20.00 software package was used for statistical analyses. Results: Day workers and shift workers exhibited excessive daytime sleepiness in 17.1% and 24.9% (P = 0.004), poor sleep quality in 41.5% and 44.3% (P = 0.374), chronic insomnia in 8% and 16.2% (P < 0.001), RLS in 4.7% and 5.3% (P = 0.818), and sleep-disordered breathing in 7.3% and 7% (P = 0.864), respectively. Conclusions: Shift work significantly compromises sleep quality. In particular, fixed night shifts or rotating shift workers experience relatively higher rates of decline in subjective sleep quality, excessive daytime sleepiness, and chronic insomnia compared with day workers.

Keywords: Insomnia, night shift, rotating shift, shift work, sleep quality

How to cite this article:
Gok DK, Ünal &, Aslan K. Sleep disorders in a shift worker population sample in Turkey. Neurol Sci Neurophysiol 2020;37:183-9

How to cite this URL:
Gok DK, Ünal &, Aslan K. Sleep disorders in a shift worker population sample in Turkey. Neurol Sci Neurophysiol [serial online] 2020 [cited 2022 Nov 29];37:183-9. Available from: http://www.nsnjournal.org/text.asp?2020/37/4/183/305385

  Introduction Top

In many parts of the world, 20% of the employed population works shifts.[1] According to a 2003 report published by the European Foundation for the Improvement of Living and Working Conditions, 8% of the employed population in Turkey worked in a shift system in 2003.[2]

Shift work causes disruptions in sleep architecture due to the misalignment between the endogenous circadian rhythm and the changes in the sleep-wake cycle required by shift-work schedules. For this reason, sleep disorders are more common among shift workers compared with workers who do not work shifts.[3] The two main symptoms of shift work-related sleep disorders (SWD) are excessive sleepiness and insomnia.[4] The effects of a shift schedule on sleep vary between individuals, and adaptation to shift work is influenced by many factors including age, sex, marital status, and genetic predisposition.[5] Approximately 10% of the United States workforce experiences sleep disturbance and sleepiness severe enough to meet the criteria for SWD.[6]

Shift workers have a higher incidence of sleep problems and poor sleep quality than fixed day shift workers.[7] Cheng et al reported that night-shift workers had a 4.33-fold higher rate of short sleep duration and 2.22-fold higher rate of insomnia than those working day shifts.[8] Yong et al . found that shift workers had shorter total sleep duration and poorer sleep quality.[9] Another study revealed that about 7% of the night-shift workers dozed off at work multiple times within a 1-month period.[1]

As a result of poor sleep quality, insomnia, and/or excessive sleepiness, shift workers have approximately twice the risk of errors and accidents on the job when compared with those working in the daytime.[10] Shift work is also a common cause of sleep-related car crashes. There is an especially pronounced increase in the risk of traffic accidents when returning home early in the morning after a night shift.[11]

There have been few studies conducted in Turkey on shift work and its effects on sleep. These studies have either been based on a small number of cases (maximum sample of 770) or targeted the same occupational groups (e.g., health-care workers).[12],[13],[14] Our aims in the present study were to investigate the sleep characteristics of shift workers, to identify SWD and health problems, and to compare these findings with the sleep characteristics of day workers in the same fields.

  Subjects and Methods Top

Study sample

The study was performed in the city of Adana, Turkey. The study sample consisted of a total of 1473 individuals, including shift workers and fixed day workers in three different fields. The employees included in the study had been working in their shift schedule for at least 1 year. The total number of individuals in each group was determined using stratified random sampling according to the weight of the three different work fields within the total sample. People working fixed day shift in the fields of health, security, and unskilled/semi-skilled labor were included in the study for comparison with the shift workers. Hospitals and factories in the Adana metropolitan area were selected to comprise the study population. One university hospital and three hospitals operating under the Public Hospitals Administration (hospitals with more than 500 inpatients) were contacted by submitting a formal written request. For the laborers and security guards, permission was acquired by contacting the managers of selected factories in writing, by phone, and in person. The workers completed the survey in person at their workplace during suitable times, supervised by two sleep technicians and a physician. Only 1473 of the 3250 selected workers completed the survey. This was attributed to several factors, one of which was the length and detailed nature of the questionnaire, which took about 15 min to complete. Furthermore, the participants all worked in branches with busy schedules, and it was sometimes difficult to find suitable times and places to conduct the survey. As a result, most participants had to complete the forms during lunch or break times. All 1473 respondents were included in the study. The study received Ethical Approval from Çukurova University Research Ethics Committee.


The data collection tool used in the study was a survey of 132 questions entitled “Survey on daily life, health, and sleeping habits,” which was adapted from the standardized questionnaire used in the Turkish Adult Population Epidemiology of Sleep Disorders study. The questionnaire was prepared by the executive board of the Turkish Sleep Medicine Society, and specialists from the Center for Social Research were involved in its design. The draft questionnaire was revised and finalized after a pilot study was conducted in centers in Istanbul, Ankara, Izmir, and Kayseri, and in another series of hospitals in Istanbul.[15]

The questionnaire included items regarding the subjects' demographic data, education level, socioeconomic status, shift schedule, accompanying health problems, sleep disorders, and sleeping habits. The questionnaire incorporated the Epworth Sleepiness Scale (ESS) to assess excessive daytime sleepiness, the Pittsburgh Sleep Quality Index (PSQI) to evaluate sleep quality, the Berlin Questionnaire to evaluate disordered breathing during sleep, the Restless Legs Syndrome (RLS) scale, and questions about insomnia.

The relationship between chronic diseases such as cancer, hypertension, chronic otorhinolaryngologic diseases, diabetes mellitus, goiter, psychiatric diseases, and shift systems was evaluated. The participants were asked whether they had experienced any occupational or traffic accidents in the last year to evaluate the relationship between accidents with shift work.

Scales used to define and assess sleep disorders as follows:


An affirmative response to any of the criteria below from the 4th edition of Diagnostic and Statistical Manual of Mental Disorders was accepted as an insomnia symptom:

  1. Difficulty falling asleep at least three times a week for a month or more;
  2. Sleep interruption with difficulty going back to sleep at least three times a week for a month or more;
  3. Waking early in the morning at least three times a week in the last month.

Sleep-related movement disorders

These include RLS, periodic limb movement disorder, sleep bruxism, and sleep-related leg cramps.

RLS is defined as unpleasant feelings of tingling, restlessness, and pain in the legs when at rest that occurs frequently (5–15 times/month) or almost every day (16 times or more per month). Other criteria are that it involves one or the other leg at different times, symptoms increase at night and are relieved by movement, and it interferes with sleep.[16] Respondents answering “yes” to all five components were evaluated as having RLS symptoms.

Excessive daytime sleepiness

This was assessed using the Turkish version of the ESS. The original scale was developed in 1991 by Johns.[17] Items are scored from 0 to 3, and individuals with total scores of 10 or more are diagnosed as having excessive daytime sleepiness.

Sleep-disordered breathing

The Berlin questionnaire assesses risk of breathing disorders during sleep through 10 questions regarding body mass index, snoring, sleep state, and blood pressure. The scale includes three separately evaluated categories; individuals with positive results in at least two of the three categories were considered at high risk for obstructive sleep apnea syndrome (OSAS).

Sleep quality

The PSQI was used to measure subjective sleep quality in the last year. This index was developed in 1989 by Buysse et al .[18] The PSQI assesses subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction in a total of 19 items in 7 scales, with each item scored from 0 to 3 points. Total score is the sum of the subscales and ranges from 0 to 21. A score of 5 or over indicates insufficient sleep quality, with 89.6% sensitivity and 86.5% specificity, and corresponds to severe disruption in at least two areas or moderate disruption in three areas mentioned above.

Statistical analysis

The SPSS for Windows, Version 20.0. (IBM Corp., Armonk, NY) package was used for statistical analyses. Descriptive statistics and prevalence of sleep disorders and their symptoms were calculated for the shift work group and the fixed day shift group. Factors related to sleep disorders were analyzed and comparisons were made between shift workers and those who only worked days. The Chi-square test or Fisher's exact test was used in the comparisons. Multivariate logistic regression analysis including age, sex, and chronic diseases was used to determine the factors associated with sleep disorders (excessive daytime sleepiness, poor sleep quality, and insomnia).

  Results Top

A total of 1473 participants were included in the study, 21.5% (n = 316) of whom worked only daytime hours and 78.5% (n = 1157) worked night shifts or rotating shifts. The mean age of the participants was 33.74 ± 7.9 (minimum–maximum: 18–57) years. The baseline characteristics of the participants such as sex, age, and work schedule are shown in [Table 1]. The basic demographic characteristics of the three work schedule groups are shown in [Table 2].
Table 1: Demographic data of the participants

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Table 2: Demographic data by work schedule

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ESS scores of ≥10 indicating excessive daytime sleepiness were observed in 24.9% of the shift workers and 17.1% of the fixed day workers (P = 0.004). PSQI scores of ≥5 denoting poor sleep quality were noted in 44.3% of shift workers and 41.5% of fixed day workers (P = 0.374). Chronic insomnia was detected in 16.2% in shift workers and 8% in fixed day workers (P < 0.001). Shift workers showed a 5.3% rate of RLS and 7% had risk for sleep-disordered breathing, but there was no statistically significant difference between the night and rotating shift workers and fixed day workers (P = 0.864 and P = 0.818, respectively) [Table 3].
Table 3: Comparison of sleep disturbances in shift worker and fixed day-shift work

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When the participants were grouped as those with fixed day working, fixed night shifts, and rotating shift work, ESS was ≥10 in 17.1% (n = 54) of day workers, 25% (n = 13) of night shift workers, and 24.9% (n = 275) of rotating shift workers (P = 0.016). PSQI was ≥5 in 43% (n = 136) of day workers, 57.7% (n = 30) of night-shift workers, and 43.3% (n = 477) of rotating shift workers (P = 0.115). The Berlin questionnaire for sleep-disordered breathing yielded scores of 2 or higher for 7% (n = 22) of day workers, 7.7% (n = 4) of night-shift workers, and 5.1% (n = 56) of rotating shift workers (P = 0.343). RLS was detected in 4.6% (n = 15) of fixed day workers, 5.8% (n = 3) of fixed night-shift workers, and 5.3% (n = 58) of rotating shift workers (P = 0.920).

According to our multivariate logistic regression, independent risk factors for excessive daytime sleepiness included female sex (odds ratio [OR]: 1.711, 95% confidence interval [CI]: 1.316–2.223), rotating shift work compared with fixed days (OR: 2.156, 95% CI: 1.538–3.049), alcohol use (OR: 1.586, 95% CI: 1.173–2.145), presence of chronic pulmonary disease (OR: 2.505, 95% CI: 1.360–4.611), and hypertension (OR: 2.243, 95% CI: 1.134–4.438) [Table 4].
Table 4: Risk factors for excessive daytime sleepiness in shift workers

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Risk factors for poor sleep quality were employment as a health-care worker (OR: 2.019, 95% CI: 1.246–3.270) or laborer (OR: 2.036, 95% CI: 1.367–3.034) compared with security guard; rotating shift work (OR: 1.501, 95% CI: 1.105–2.216) compared with fixed day work; presence of chronic pulmonary disease (2.403, 95% CI: 1.167–4.948), gastrointestinal disease (OR: 1.910, 95% CI: 1.237–2.949), diabetes (OR: 5.414, 95% CI: 1.247-23.498), eating before bed once or twice (OR: 1.961, 95% CI: 1.449–2.652) or more per week (OR: 2.223, 95% CI: 1.604–3.081) compared with not eating before bed and smoking (OR: 1.460, 95% CI: 1.124–1.896), and alcohol use (OR: 1.552, 95% CI: 1.129–2.134) [Table 5].
Table 5: Risk factors for poor sleep quality in shift workers

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Risk factors for insomnia were employment as a healthcare worker (OR: 1.774, 95% CI: 1.033–3.406) compared with security guard; night-shift work (OR: 3.053, 95% CI: 1.308–7.122) or rotating shift work (OR: 3.480, 95% CI: 2.127–5.694) compared with fixed day work; presence of cardiac disease (OR: 3.365, 95% CI: 1.314–8.618), chronic lung disease (OR: 2.138, 95% CI: 1.039–4.400), gastrointestinal disease (OR: 1.755, 95% CI: 1.084–2.841), eating before bed once or twice (OR: 1.885, 95% CI: 1.280–2.778), or more per week (OR: 2.309, 95% CI: 1.563–3.410) [Table 6].
Table 6: Risk factors for insomnia symptoms in shift workers

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Although shift workers tended to have higher rates of cardiac disease, hypertension, chronic otorhinolaryngologic diseases, diabetes mellitus, goiter, psychological illness, and cancer, the differences between the groups were not statistically significant.

The participants were asked whether they had experienced any occupational or traffic accidents in the last year. Comparisons between these data and other related sleep disorders and work schedules showed that occupational accidents were reported by 4.6% (n = 15) of fixed day workers, 11.5% (n = 6) of fixed night-shift workers, and 4.9% (n = 54) of rotating shift workers (P = 0.096). Occupational accidents were most common among night-shift workers and occurred at comparable rates in the fixed day and rotating shift groups, but the differences were nonsignificant. Traffic accidents in the last year were reported by 3.4% (n = 11) of fixed day workers, 5.8% (n = 3) of fixed night-shift workers, and 2.2% (n = 24) of rotating shift workers. Similarly, night-shift workers tended toward a higher risk of traffic accidents than workers in other work schedules, but the difference was not statistically significant (P = 0.163).

  Discussion Top

The aim of this study was to examine the association between shift work and sleep disorders. In our study, fixed day workers and night or rotating shift workers exhibited excessive daytime sleepiness and poor sleep quality, respectively.

Shift workers had a 2.1-fold higher risk of excessive daytime sleepiness than fixed day workers [Table 4]. In our study, rotating shift work in particular was associated with daytime sleepiness. Similar earlier studies also showed that night and rotating shift work were associated with higher risk of excessive sleepiness compared with day work.[7],[19]

Our assessment of PSQI subcomponents indicated that shift workers had poorer sleep quality compared with fixed day workers. Poorer sleep quality in shift workers has been emphasized previously in the literature.[14],[20] In a recent study, Thach et al . reported that shift work was significantly and independently associated with increased odds of poor sleep quality in their sample of workers. In our study, rotating shift schedule in particular was associated with impaired sleep quality.[21] Several factors can contribute to poor sleep quality on rotating shifts. Rapid and continuous or counterclockwise rotation on shifts leads to circadian rhythm disruption and has more negative effects on quantity and quality of sleep.[22] Female sex, smoking, alcohol use, and gastrointestinal diseases were identified as risk factors for poor sleep quality, which supports the literature.[23],[24]

Many environmental factors may influence the prevalence of insomnia. Several factors such as sex, age, marital status, occupation, shift schedule, education level, lifestyle behaviors, and income have been associated with insomnia. In the workplace, insomnia was associated with night work and a short time duration for recovery between shifts.[25] A recent previous study showed that shift work was an important risk factor for insomnia.[26] In our study, the prevalence of insomnia was 8.2% in day workers, 21.2% in night-shift workers, and 15.9% in rotating shift workers (P < 0.001). These findings are consistent with previous studies reporting higher rates of insomnia in night-shift and rotating shift workers compared with day workers.[8],[19]

In our study, we were unable to show differences in sleep respiratory events as assessed using the Berlin questionnaire based on shift work and shift schedule (P = 0.963). However, we did not conduct polysomnography in our study and did not interview the participants' family members or bed partners in relation to apnea. Previous polysomnography studies demonstrated that night shifts exacerbated the symptoms of OSAS, and recommended that patients with OSAS should avoid working night shifts.[27],[28] A recent study using the Berlin questionnaire revealed that the prevalence of OSAS was higher among shift workers compared with the general population.[29]

Shift work is reported to cause oxidative stress by disrupting the circadian rhythm, thus triggering or exacerbating RLS symptoms.[30] A study conducted in Turkey involving health-care personnel working night shifts reported that RLS was twice as common among night-shift workers than in their colleagues.[14] In our study, however, there was no significant difference between the shift groups and day group with regard to RLS (P = 0.708). Furthermore, in our study, we found that the prevalence of RLS among shift workers was nearly equal to the general population in Turkey.[15] This is consistent with another study that found no correlation between RLS and shift schedules.[31] In a recent study, Uekata et al . reported that the prevalence of RLS among Japanese female nursing staff working shifts was nearly equal to that among the general population.[32] The presence of concomitant diseases in our study was assessed through the participants' self-reports and was not confirmed by laboratory tests. This is a limitation of our study because the possibility of comorbidities is underestimated.

The adverse effects of shift work on various chronic diseases such as cardiovascular disease, ulcers, reflux, diabetes, and cancer have been investigated in numerous studies in recent years, and shift workers were found to have a greater risk of developing chronic diseases and breast cancer compared with day workers.[33],[34] Although cardiac disease, hypertension, chronic otorhinolaryngologic conditions, diabetes mellitus, goiter, psychiatric illness, and cancer were more prevalent among the shift workers in our study, the results were not statistically significant. We interpreted this as an indicator that patients with chronic disease avoided jobs that involved shift work. Of the two nurses with cancer in our study, both had a history of breast cancer; one had been working in a shift system for 18 years, and the other did shift work for 20 years and switched to a daytime schedule after her cancer diagnosis.

The alertness and concentration problems resulting from shift work lead to occupational accidents due to impaired wakefulness during working hours, as well as traffic accidents after working hours.[11],[35],[36] Vedaa et al . reported that night shifts and quick-return shifts were both associated with the risk of self-reported work-related accidents, near accidents, and dozing off at work.[37] In our study, night-shift work was found to be slightly more risky in terms of occupational and traffic accidents compared with day and rotating shift work, but the differences were not statistically significant (P = 0.096, P = 0.163).

The main limitation of our study is that it is based only on self-reported data and not on objective measures, clinical examination findings, or laboratory analyses. Furthermore, the lack of psychiatric assessments is another limitation because psychosocial factors are related with worse sleep quality.

  Conclusion Top

Shift work may be extremely detrimental to sleep quality, leading to sleep disorders. Raising awareness among both employers and employees of sleep disorders associated with shift work will lead to improvements in shift workers' quality of life and working efficiency. Therefore, further clinical studies should be performed on this topic. To prevent these consequences, working hours should be regulated, people who are able to acclimate to shift work should be placed in these positions, and employers should arrange shift schedules in accordance with sleep physiology.


We are thankful to the Turkish Sleep Medicine Society for providing financial support at the stages of publication and application of the questionnaire we used in our study, and for allowing us to use the questionnaire form developed by them; and also to the Scientific Research Project Coordination Unit of Çukurova University which provided financial support. In addition, we are grateful to the technicians of the Çukurova University Sleep Laboratory who gave their kind support at the application stage of the questionnaires and to Public Hospitals Union for their contributions by providing permit for the application of the questionnaires in the subsidiary hospitals.

Financial support and sponsorship

This study was supported by Turkish Sleep Medicine Society.

Conflicts of interest

There are no conflicts of interest.

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  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]


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