Influence of sleep duration and quality on depression symptoms among nurses during the Omicron outbreak: a cross-sectional survey

The COVID-19 outbreak has emerged as one of the most widespread significant public health events in recent history. Through concerted efforts, the spread of COVID-19 has been largely contained within China. However, on 26 November 2021, the World Health Organization (WHO) announced the emergence of a novel variant of SARS-CoV-2, named Omicron (B.1.1.529)[1]. Despite its apparent decline in virulence, Omicron has shown increased transmissibility, presenting new challenges for epidemic control measures [2]. Since the confirmation of an Omicron case in Zhejiang Province in August 2022, the number of confirmed cases has risen rapidly within a span of ten days, including 134 locally transmitted cases and 480 asymptomatic carriers [3]. Consequently, the government has implemented stringent control measures, such as mass nucleic acid testing, home quarantine protocols, and city closures to curb the resurgence of this virus in Zhejiang Province. The ongoing Omicron wave of COVID-19 in Zhejiang Province has exerted significant pressure on various aspects of daily life, including health concerns, economic stability, and social interactions, particularly impacting healthcare workers [4]. The rapid spread of the Omicron variant has not only overwhelmed healthcare systems but also significantly impacted the mental health of medical staff [5]. Studies have shown that the increased stress and workload during the COVID-19 pandemic are associated with increased rates of depression among healthcare workers [6].

Previous studies have shown that nurses already face a risk of depression, with prevalence rates ranging from 19.6% to 26.03% before the pandemic [7, 8]. However, the pandemic has exacerbated this situation, with recent estimates suggesting a further increase in depression rates among nurses to approximately 35%-43.61% [5, 9, 10]. This increase was attributed to factors such as increased workload, fear of infection, emotional exhaustion, and disrupted work‒life balance [11]. Additionally, social isolation and exposure to patient suffering increase stress and mental health issues among nursing staff [12].

Sleep quality encompasses an individual's overall satisfaction with their sleep experience, which includes dimensions such as sleep initiation, sleep maintenance, sleep duration, and the level of refreshment felt upon waking. This concept is distinct from sleep duration, which specifically refers to the total hours of sleep one accumulates [13]. Sleep quality and duration are crucial aspects of sleep health, with empirical evidence demonstrating that nurses, especially those engaged in night shifts or with irregular work schedules, frequently experience disrupted sleep patterns [14]. These factors can precipitate difficulties in sleep initiation, frequent nocturnal awakening, and diminished sleep efficiency, all of which have been shown to adversely affect sleep quality. Impaired sleep is recognized as both a risk factor and a symptom of depression, with inadequate duration and quality being among the main determinants of mental health disorders [15‐17]. The circadian cycle, which regulates the production of cortisol and melatonin, as well as the sleep‒wake cycle, can explain mental health disorders and sleep patterns. Disruption of the circadian cycle due to changes in cortisol levels that plays an important role in stress-related dysregulation, is linked to mental and physical health [18, 19]. The circadian cycle has been disrupted during the COVID-19 pandemic due to changes in people’s social activities and routine life [20]. During the COVID-19 pandemic, increased pressure on healthcare systems, fear of infection, and emotional stress have led to a worsening of sleep impairment among nurses [21]. Previous reports have indicated a significantly higher prevalence of sleep disturbances among nurses during the COVID-19 outbreak, with rates ranging from 52.7% to 81.5% [21‐26], which is notably higher than the 39.2% prevalence rate of sleep disturbances among healthcare workers identified in a pre-pandemic meta-analysis [27].

While previous research has consistently demonstrated a strong association between sleep duration, sleep quality and depression, the relationship between nurses' sleep and depression during the Omicron variant has yet to be explored. Given the unique stressors introduced by the pandemic, including increased workload, fear of infection, emotional exhaustion, disrupted work‒life balance, and social isolation, stress levels among nurses have significantly increased. It remains unclear whether the relationship between sleep and depression differs from what was observed in pre-pandemic studies. This study aims to explore the influence of sleep duration and quality on depression symptoms among nurses during the Omicron outbreak, addressing a significant gap in the current body of research.

This study is the first to explore the associations between the duration and quality of sleep and depression symptoms among Chinese nurses during the Omicron epidemic. Our findings demonstrated that shorter duration and poorer quality of sleep were independently associated with depression symptoms among Chinese nurses during the Omicron epidemic.

This study suggested that a shorter duration was associated with depression symptoms, and this relationship was strong and independent, which is consistent with the findings of previous studies despite the variations in the assessment instruments for depression symptoms across studies [36‐39]. Some studies have suggested an inverted U-shaped relationship between sleep duration and depression symptoms [40]. Specifically, sleep duration < 8 h is associated with a significantly lower risk of incident depression. When sleep duration ≥ 8 h, the risk of depression increased significantly with an increase in sleep duration. However, owing to the limited number of nurses reporting excessive sleep, we did not conduct a correlation analysis between excessive sleep duration and depression symptoms among the nurses. Additionally, this study revealed that 69.2% of nurses experienced poor sleep quality, and 40.4% exhibited depression symptoms, which is in line with previous research conducted during the COVID-19 pandemic [5, 23]. These rates were notably higher than those reported prior to the pandemic [8, 27].

This study revealed that in addition to sleep quality and duration, female nurses were more prone to exhibiting depression symptoms. This finding was consistent with earlier findings and was most likely be attributed to a confluence of biological, psychological, and social factors that are known to influence the prevalence of depression symptoms among women [41]. Moreover, nurses with a fear of infection, a heavier patient load, and higher HADS-Anxiety scores were also found to be at a greater risk of experiencing depression symptoms. The relationship between these factors and depression symptoms among nurses is complicated. For example, the fear of infection, a significant stressor, especially in the context of the COVID-19 pandemic, could lead to avoidance behaviors that might impact work performance and contribute to feelings of inadequacy, thereby increasing the risk of depression [42]. Additionally, the heavier patient load may lead to increased work stress, which could lead to emotional exhaustion and a perceived lack of control over one's work environment, both of which are linked to COVID-19 depression [43]. Furthermore, higher HADS-Anxiety scores suggested a close relationship with depression, as anxiety often cooccurs with depression symptoms [44]. These findings underscore the complex relationship of personal attributes, occupational demands, and health-related factors in shaping the mental health landscape of nursing staff.

Previous research has proposed several potential mechanisms underlying the link between short sleep duration and depression symptoms; one is that disrupted sleep independently contributes to the risk of inflammatory disorders and major depressive disorder [45]. Sleep disturbance may increase vulnerability to depression by altering neural sensitivity to inflammation while potentially increasing affective sensitivity to cytokines. Sleep disturbance acts as a vulnerability factor and drives an increase in inflammatory states, such as an infectious challenge or triggers psychological stress, which in turn contributes to the development of depression symptoms [46]. A systematic review and meta-analysis have demonstrated that sleep disturbance is associated with elevated levels of inflammatory markers [47]. Interestingly, inflammation not only has a relationship with depression, but also plays a significant role in pathophysiology [48]. Second, the association between insufficient sleep and depression symptoms can be explained by their shared links to obesity, physical health problems, and impaired work performance [49]. Third, inadequate sleep duration has been associated with emotional difficulties, risky behavior, and suicidal tendencies among adolescents, thus increasing their susceptibility to depressive symptoms [50]. Furthermore, optimizing both the quality and duration of sleep can serve as an important target to promote a healthy gut microbiota composition [51], the gut microbiota refers to the diverse community of microorganisms residing in the gastrointestinal tract, which play a crucial role in various aspects of health, such as digestion, immune function, and even mental health. The microbiota-gut-brain axis is a bidirectional communication system that connects the central nervous system with the enteric nervous system through neural, endocrine, and immune pathways. This axis is increasingly recognized for its influence on neurological diseases, including depression [52, 53].

The subgroup analysis results revealed a significant correlation between sleep duration, sleep quality, and depressive symptoms within specific groups of nurses. Compared with male nurses, female nurses are more prone to exhibiting depression symptoms and sleep disturbances due to physiological cycles, hormonal fluctuations, and societal role expectations [41]. Married nurses need to balance work and family, as family pressures and worry about family can exacerbate psychological burdens [54]. Nurses with high exposure risk constantly worry about infection, and their tension and fear affect sleep and depression symptoms [55]. Nurses experiencing increased work intensity have high physical and mental consumption, making it difficult to rest adequately, thereby increasing the incidence of depression symptoms and sleep disorders. [24]. Nurses with insufficient experience and primary titles are more likely to feel anxious and doubt themselves when facing complex nursing tasks [56]. Undergraduate-educated nurses have greater expectations for career development, and the gap between reality and ideals triggers stress [57]. We acknowledge the variability in results across different subgroups, which may be attributed to a multitude of factors including individual differences in coping mechanisms, work-related stress, and personal circumstances.

In conclusion, this study highlighted the association between shorter sleep duration and poorer sleep quality with depression symptoms among nurses during the Omicron outbreak. It is imperative that healthcare systems addressing sleep and depression symptoms among nursing staff throughout the pandemic. We recommend the development of targeted interventions to meet the unique challenges faced by nurses, which may include sleep hygiene education, stress management programs, and mental health support services.

The strengths of our study include the relatively large sample size and the effects of adjusting for various levels of work closely related to depression symptoms. There are several limitations to this study. First, it is important to note that while the cross-sectional design utilized in this study provides significant benefits, such as practicality, cost-effectiveness, and the capacity to yield preliminary insights, it inherently lacks the ability to establish causality. Given this limitation, we advocate for the adoption of longitudinal study designs in future research endeavors. Second, the use of self-reported data to measure sleep duration, sleep quality, and depression symptoms. While self-report methods were commonly used in psychological and health-related research, they were subject to various biases, such as recall bias and response bias, which could potentially affect the accuracy of the information collected. To address the limitations of self-reported data, we recommend that future studies incorporate objective measures of sleep and mental health, such as clinical assessments and polysomnography to enhance the accuracy of data collection. Additionally, although we controlled for several demographic variables, unmeasured confounders such as socioeconomic status, work hours, and medical history could influence the relationships between sleep quality, sleep duration, and depression symptoms. Therefore, we recommend that future studies endeavor to include and control for these additional confounding factors to enhance the accuracy and reliability of the findings. More importantly, selection bias in the sample is another limitation that should be noted. Our sample was drawn from nurses working in 11 different hospitals in Jinhua, Zhejiang Province, which may not be representative of the broader nursing population in China or other regions. Future research should aim to recruit participants from a wider variety of locations and settings to enhance the external validity of the results.