Introduction

Sleep has received considerable attention as an important reference point for mental health (Cho 2014). Chronic sleep deprivation can worsen medical and mental health conditions, making work difficult. For example, the risk of medication errors is associated with poor sleep quality among nurses (Di Simone et al. 2020). Poor sleep quality is also associated with a reduced quality of life among nurses. Female nurses with a good quality of life had significantly higher sleep quality than female nurses with moderate or poor quality of life. The American Academy of Sleep Medicine reports that 30%–35% of adults in the United States have short-term insomnia symptoms (Kunzweiler et al. 2016). The Pittsburgh Sleep Quality Index (PSQI) was used in a cross-sectional survey, and the results demonstrated that depression was associated with sleep quality, with PSQI scores ranging from 0–5 representing normal sleep, 6–10 indicating mild sleep disorders, 11–15 indicating moderate sleep disorders, and indicating 16–21 severe sleep disorders(Lu et al. 2023). Insomnia is among the most common sleep disorders worldwide; among nurses, insomnia is common because of long shifts. In a survey of 4245 nurses, 38.7% reported experiencing sleep disorders (Jiang et al. 2021). Another study reported that 34.30% of 207 nurses had poor sleep quality (PSQI total score > 10) (Zheng et al. 2021). Additionally, over 50% of nurses reported poor sleep quality in another study (Huang et al. 2021).

Shift work is commonly defined as any type of work outside the standard working time (8:00–18:00) and includes various working-time arrangements. As hospitals operate around the clock, nursing staff have continuous work schedules (Li et al. 2019). A meta-analysis showed that sleep disorders are common among medical and health personnel in China, with a prevalence of 39.2%, which is much higher than that in the general population (Qiu et al. 2020). The incidence of sleep disorders varies between departments, fluctuating between 39.02% and 80% (Dong et al. 2020; Guo and Wang 2019). Nurses may need to stay up all night and work several consecutive 12-h shifts. Night shift work is the primary cause of sleep disorders, with 57% of night shift nurses suffering from sleep disorders (Zhang et al. 2016). However, owing to the nature of their work, nurses are at a higher risk of decreased sleep quantity and quality, and sustained sleep deprivation (Akerstedt 2003; Roveda et al. 2021; Zhang et al. 2019). Long-term sleep deprivation leads to severe mental dullness, memory loss, slow response, fatigue, irritability, and even potential depression, and suicidal thoughts (Mieda et al. 2013; Rosado et al. 2015). Additionally, night work affects not only the personal health of nurses but also the quality of their work, mental health, and treatment of patients, leading to errors and accidents (Feleke et al. 2015; Kling et al. 2010). Fatigue due to poor sleep reduces nurses’ ability to focus and make good decisions, which can lead to errors and potential injuries (Ce et al. 2020; Horwitz and McCall 2004; Perez-Fuentes et al. 2019; Sun et al. 2019).

Previous studies have indicated that work stress may be directly related to poor sleep quality among nurses in different general hospital departments (da Rocha et al. 2010; Han et al. 2016). Stress in the nursing profession includes significant responsibilities, high risk, constant exposure to diseases, injuries, and even death (Gao et al. 2012). Long-term work stress leads to fatigue, anxiety, depression, and other psychological problems affecting sleep quality (Li et al. 2015). A review of the literature on easy coping styles and sleep quality found that positive coping styles can help patients improve their sleep quality (Chen et al. 2022; Ren et al. 2021; Tan et al. 2022). Positive coping style refer to the use of positive attitudes to cope with problems encountered, including participation in leisure activities, confiding in others, positive thinking, and exercise. A meta-analysis of the effect of exercise on sleep quality found a significant effect in favour of intervention (Banno et al. 2018). Another meta-analysis found significant effects favouring yoga compared to inactive controls for sleep quality (Sivaramakrishnan et al. 2019).

Therefore, we analyzed the sleep quality of nurses in the post-pandemic era and investigated whether coping styles and other demographic and occupational characteristics affected their sleep quality. Investigating the factors that affect nurses’ sleep quality in critical situations will help public health systems develop strategies to improve the sleep quality of their staff and, ultimately, their quality of life.

Methods

Design, setting, and participants

This cross-sectional study investigated nurses who worked in Changde (Hunan Province, China) Hospital and asked them to complete a questionnaire from 10 April to 15 May 2023. The questionnaire was created using Wenjuanxing (www.wjx.cn), an online crowdsourcing platform in mainland China, and an anonymous self-assessment questionnaire was sent to nurses via the Internet. Before participants completed the questionnaire, the informed consent page presented two options (agree or disagree). Only participants who chose “agree” were linked to the questionnaire page, and the nurses could quit the survey at any time.

Convenience sampling and an online questionnaire (WeChat) were used. The sample size was calculated using a single population proportion formula n = (Zα/2)2 P(1 − P)/d2 (Tesfaye et al. 2021). Where Zα/2 is the confidence level (at α = 0.05, Zα/2 = 1.96), P = expected proportion of the sleep disorder (the incidence of sleep disorder in the preliminary survey was 60%), and d2 = margin of error (d2 = 0.05 × 0.05). The calculated minimum sample size, n = (1.96)2 × 0.6 (1–0.6)/ (0.05)2 was 369. Considering the addition of a 20% contingency for nonresponse, the sample size was estimated to be 443 participants, and the study sample included 1022 participants. The inclusion criteria for nurses were as follows: (a) licensed registered nurses, (b) practising nursing at the clinical front line, and (c) participating in night shift rotations. Nurses on leave or with serious physical or mental problems, in the hospital nurses over 40 years of age who exempted from evening night shifts were excluded.

Questionnaires

The questionnaire included four parts: sociodemographic characteristics of nurses, factors related to shift work, the Pittsburgh Sleep Quality Index (PSQI), and the Simplified Coping Style Questionnaire (SCSQ).

Sociodemographic questionnaire

In editing the sociodemographic questionnaire, we included sociodemographic factors that may affect sleep disorders through a literature review. The basic demographics included sex, age, education, marital status, race, years of work, professional title, and hospital department.

Questionnaire about related characteristics in nurses on shift work

Before editing the questionnaire about nurses’ shift work-related characteristics, we prepared the questionnaires by taking into account what was covered in the literature and the actual situation. During the preparation process, we organised discussions with nursing managers with research experience, pre-surveyed night shift nurses with the questionnaires, and organised another expert meeting based on the pre-survey results to ensure the scientific applicability of the questionnaires. The contents of the questionnaire on related factors in nurses with shift work included the frequency of night duty, feelings while on night duty, influence of night shift work on sleep, satisfaction with the condition of night duty, history of sleep disorders, attended training and learning after night duty, working intensity of night duty, satisfaction with night duty, economic income, personality type of nurses,frequency of exercise, humanistic nursing, job morale, and prospects for career development.

Pittsburgh sleep quality index (PSQI)

The sleep quality of the respondents was assessed using the PSQI (Buysse et al. 1989). The sleep quality index contains 19 items across seven dimensions: subjective sleep quality, sleep latency, sleep duration, sleep efficiency, sleep disturbance, sleep medication use, and daytime dysfunction (Buysse et al. 1989). Each item was assessed on a 4-point Likert scale, and the total score ranged from 0 to 21, with a higher score indicating a higher level of sleep disorders or worse sleep quality. Previous studies have used five as the cutoff value for sleep disorders, whereas recent studies have used a cutoff value of seven, which shows higher sensitivity and specificity in identifying sleep disorders in the Chinese population (Giorgi et al. 2018; Kong et al. 2018; Xiong et al. 2019). Therefore, a value > 7 of the PSQI score was considered to indicate the presence of sleep disorders in our study. In Yan’s study, Cronbach’s α of the PSQI is 0.79, and the confirmatory factor analysis of the comparative fit index (CFI) is 0.76 (Yan et al. 2021).

Simplified coping style questionnaire (SCSQ)

The SCSQ contains 20 items and two subscales: positive coping style (Items 1–12) and negative coping style (Items 13–20) (Tan et al. 2022). The subscale score reflects participants’ different coping style preferences, with the “positive coping” dimension mainly reflecting the characteristics of positive coping and the “negative coping” dimension reflecting the characteristics of negative coping (Wang et al. 2020). The SCSQ includes a variety of positive coping styles, including several active coping styles, such as finding hobbies, actively participating in sports and cultural activities, seeking advice from friends and family, and finding solutions (Banno et al. 2018). For the Chinese population, Cronbach’s alpha of the SCSQ for the positive and negative coping subscales was 0.87 and 0.81, respectively, and the scale had good reliability and validity (Zhang et al. 2020). In our study, the Cronbach’s α coefficient and the CFI of the SCSQ were 0.76 and 0.82 respectively.

Statistical analysis

SPSS 22.0 software was performed using for statistical analysis, including frequencies, percentages, mean values, standard deviations of sample demographics and symptoms, and descriptive statistics for the PSQI and SCSQ. Data were expressed as mean ± standard deviation, frequency, and percentage. Pearson’s correlation analysis was used to show the relationship between the PSQI and SCSQ scores. Univariate and multivariate analyses were used to explore factors associated with sleep quality among night shift nurses. All analyses were performed using two-sided tests (P < 0.05).

Results

Demographic characteristics of the participants

Table 1 summarises respondents’ sociodemographic characteristics. Participants were predominantly female (90.90%) of Han ethnicity (92.17%), and 87.38% were over 25 years of age. Among participants, 94.03% had a bachelor’s degree, and 45.30% had been working for more than 10 years. Regarding professional levels, 443 (43.35%) were junior students, 403 (39.43%) were intermediate students, 326 (31.90%) were from medicine, and 336 (32.88%) from surgery.

Table 1 The Sociodemographic characteristics of Participants (N = 1022)
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Influencing factors in nurses with shift work

We evaluated the factors influencing nurses’ engagement in shift work and identified them based on several aspects. A total of 41.39% of participants maintained a highly optimistic attitude towards the prospects of career development, for example, 80.82% believed that nurses work much harder on night shifts than during the day, 11.64% were dissatisfied with night duty economic income, 55.28% felt unwell when on night duty, and 92.08% thought that the effect of night shift work on sleep was high. However, only 7.24% of nurses were unhappy with their job morale. The results of night duty frequency, satisfaction with night duty conditions, sleep disorder history, exercise frequency, and night duty frequency are presented in Table 2.

Table 2 The related factors in nurse with shift work (N = 1022)
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PSQI and SCSQ scores in nurses on shift work

According to the questionnaires, the total PSQI was 10.51 (2.23), 931 (91.1%) nurses had sleep disorders, the SCSQ Positive score was 17.60 (6.67), and the SCSQ Negative score was 8.79 (3.84). The PSQI and SCSQ scores are shown in Table 3.

Table 3 The PSQI scores and SCSQ scores in nurse (N = 1022)
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Correlation analysis between sleep quality and SCSQ

Pearson’s correlation analysis associated PSQI with positive and negative SCSQ scores. The results showed that sleep efficiency was positively correlated with the SCSQ Positive score power (P < 0.05), whereas sleep disturbance and daytime dysfunction were negatively correlated (P < 0.01). Sleep medication use and daytime dysfunction were positively correlated with SCSQ negative score power (P < 0.05), while sleep latency and sleep efficiency were negatively correlated with negative SCSQ scores (P < 0.05) (Table 4).

Table 4 Correlations between SCSQ scores and PSQI dimensions (N = 1022)
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Univariate and multivariate analysis on factors of sleep disorder

Demographic characteristics included sex, age, education, marital status, years of work, professional title, and factors influencing nurses’ engagement in shift work. Univariate analysis showed that age, professional title, career development prospects, frequency of night duty, frequency of exercise, training and learning after night duty, humanistic nursing, and SCSQ positive scores may be risk factors for sleep disorders that influence sleep quality (P < 0.05). Multivariate analysis showed that 36–40 years of age, frequency of night shifts (9–11 times/month, ≥ 12 times/month), and less humanistic care were risk factors for sleep disorders among night nurses (P < 0.05), whereas frequency of exercise (1 time/week), non-attendance of training and learning after night shifts, and SCSQ positivity were protective factors for sleep disorders (P < 0.05), and there were no statistically significant differences in other variables (Table 5).

Table 5 Univariate and Multivariate analysis on factors for sleep disorder (N = 1022)
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Discussion

A total of 1022 night shift nurses were included in this study, 91.1% of whom reported sleep disorders during the post-pandemic era. The prevalence of sleep disorders among nurses before the COVID-19 pandemic was 32.4%–77.4% (Dong et al. 2020; Flo et al. 2012; Khatony et al. 2020). The prevalence of sleep disorders among night shift nurses was 57% (Shao et al. 2010; Zhang et al. 2016). A meta-analysis of sleep quality among healthcare workers in 2021 showed that the prevalence of sleep disorders among healthcare workers during the COVID-19 pandemic was 18.4%–84.7% (Lin et al. 2021). One study showed that the prevalence of sleep disorders in the post-pandemic era was 48.2% (Hui-Ren et al. 2023). Our findings were higher than those of previous studies, which may be related to the different study populations and the fact that they experienced the COVID-19 pandemic.

This study investigated the factors related to nurses’ perceptions of sleep quality. The perception of sleep quality is complex and related to various subjective factors. Although previous studies have reported some links, they tended to focus primarily on work-related pressure and sleep quality. However, it is worth conducting a comprehensive analysis of these variables as they contain more extensive factors. Additionally, this study assessed the overall sleep quality of nursing staff who were frontline bedside care providers during the early COVID-19 pandemic (Hofmeyer et al. 2020). This study implies that 36–40 years of age, frequency of night shifts (9–11 times/month, ≥ 12 times/month), and less humanistic care were risk factors for sleep disorders among night nurses, whereas frequency of exercise (1 time/week), non-attendance of training and learning after night shifts, and SCSQ positivity were protective factors for sleep disorders.

Similar to previous research findings, coping methods, age, and exercise frequency were important predictive factors of nursing managers’ sleep quality during the COVID-19 pandemic in a study of nursing managers (Chen et al. 2022). Coping methods are important for shaping nurses’ sleep quality. This study analysed the relationship between sleep disorders and coping methods. The results showed that sleep quality was negatively correlated with positive SCSQ scores. Positive coping styles can reduce the risk of sleep disorders in night shift nurses. Similar results have also been found in previous studies, in which insomnia patients used more negative and less proactive coping strategies. Positive coping is negatively correlated with insomnia symptoms and psychological distress, whereas negative coping is positively correlated with these symptoms, making negative coping strategies an important factor in the sleep quality of persons with insomnia (Li et al. 2021; Ren et al. 2021). Another study implied that individuals who passively respond to stress often reduce their emotional regulation, increase their negative evaluations of stress, and experience excessive awakening before sleep, which is related to insufficient sleep (Sadeh et al. 2004). Therefore, further research should be conducted on the interaction between nursing staff stress, coping methods, sleep quality, and mental health to determine the negative coping strategies closely related to insomnia symptoms and to provide professional psychological counselling for nursing staff to develop more specific coping measures to improve their sleep quality.

Sleep problems are physiological changes that occur with age in sleep physiology (Waller et al. 2016). A previous study showed that older nurses are also at a risk of developing sleep disorders (Zhou et al. 2020). Our study showed that older nursing staff members were more likely to have sleep disorders. A survey of the general population in Sao Paolo, Brazil found that individuals aged 35 years or older experienced higher levels of sleep disorders (Maluly et al. 2020). Another study showed a higher risk of sleep disorders in female nurse managers over the age of 41 years, which may be related to menopausal status and influenced by oestrogen levels (Chen et al. 2022). In addition, compared with young people, middle-aged and older caregivers have more family responsibilities and financial burdens and are more prone to negative life events such as divorce and chronic physical illnesses (Zhou et al. 2020). Therefore, hospital managers should provide more rest time and implement humane management of older nursing staff to alleviate age-related sleep disorders.

This study found that the frequency of exercise once per week and humanized care had positive effects on the sleep quality of caregivers. Similar to the findings of previous studies, exercise is a positive response to challenges and can improve sleep quality (Chen et al. 2022; Dong et al. 2020; Otsuka et al. 2017). This may be because energy consumption, endorphin secretion, and temperature increases brought about by exercise are beneficial to nurses’ sleep and recovery (Rubio-Arias et al. 2017). Therefore, the nursing staff should be encouraged to participate in appropriate exercise training programs. Hospitals should provide appropriate exercise facilities for their staff, organize yoga training, and increase training on sleep quality-related aspects of shift nurses' sleep schedules, guidelines, and timing (d'Ettorre and Pellicani 2020; Wirth et al. 2023). This environment limits exercise before bedtime (Carter et al. 2013).

Shift work, which involves working arrangements outside traditional daytime working hours, often leads to a slow transition of the internal circadian rhythm clock to working hours—that is, the circadian rhythm is not synchronised (Arendt 2010; Boivin and Boudreau 2014; Galasso et al. 2021; Gomez-Garcia et al. 2016). Although it cannot be definitively determined, desynchronisation of the circadian rhythm may partially contribute to various health problems (Akerstedt 1998; Skipper et al. 1990). One study showed that the sleep quality of shift nurses was lower than that of day nurses (P < 0.05) (Chang and Li 2022). Additionally, excessive participation in training by nursing staff reduces rest time and, to a certain extent, increases fatigue and reduces sleep quality. Therefore, shift nurses should implement sleep management strategies, such as avoiding interference with their sleep–wake rhythms and improving sleep quality, which should be an effective strategy for reducing fatigue.

In our study, there was no significant difference in sleep quality between males and females. However, another study has reported contradictory results. In one study, women reported a higher degree of sleep quality deterioration than men (Xu et al. 2022). Similar to previous research results, women were more likely than men to have adverse mental health problems (Chen and Gueta 2016; Dinis and Braganca 2018; Fatima et al. 2016). Gender differences exist in factors influencing psychological health (Lee and Lee 2011; Riecher-Rossler 2017; Zhang et al. 2022). Multivariate logistic regression analysis in another study showed that the rate of poor sleep quality was higher among male medical staff (Zheng et al. 2021). This finding may be related to the high proportion of female nurses in China. A study found that the proportion of female nurses was 91% in New Zealand and 90.4% in the Netherlands (Harding et al. 2018). By 2022, the proportion of female nurses in China will be 97%, which is higher than in developed countries (China 2022). These contradictory results highlighted the need for further studies with larger sample sizes.

Limitations

This study had several limitations. First, owing to its cross-sectional design, causal relationships between the identified factors and sleep quality could not be determined. Further longitudinal studies are required to verify these findings. Second, the study used data from a single hospital,and nurses over 40 years had been excluded. Therefore, our results may not apply to other hospitals.

Conclusion

The sleep quality of medical staff, especially nurses, has been affected in the post-pandemic era. Hence, it is important to design optimal sleep management strategies for employees who are prone to sleep disorders, such as experienced nurses. This can be achieved through sleep hygiene education and by enhancing the humanistic support provided to nurses.