Sleep Quality in Shift-Working Nurses: Subjective and Objective Evaluation

Sleep quality represents an individual's subjective satisfaction with various aspects of the sleep experience, and it is recognized as an essential component of overall health and well-being. Adequate sleep contributes to optimal physical, psychological, and functional health, thereby enhancing quality of life [1,2]. Conversely, chronic sleep deprivation has been found to be associated with a wide range of adverse health outcomes, including metabolic and cardiovascular diseases, inflammation, depression, anxiety, and cognitive dysfunction, and it may even increase overall mortality risk [3,4]. Furthermore, longitudinal studies indicate that improvements in sleep duration and quality can lead to measurable enhancements in individuals' quality of life [5].

Shift work is an integral and indispensable part of the healthcare system because it ensures continuous care for patients 24 h a day, 7 days a week. Although rotating shift work is necessary, it brings about numerous challenges for physiological and psychological processes, especially the circadian rhythm, which regulates the cycle of sleep and wakefulness [6,7]. Working at night during the period when the organism is biologically programmed to rest leads to circadian desynchrony. The consequences of this are disturbances to the internal clock, acute lack of sleep, frequent sleep disorders, and chronic fatigue and exhaustion [6,7,8]. Numerous studies have shown that nurses who work night shifts experience significantly poorer sleep quality compared with those who work exclusively during the day [9,10]. According to recent studies, as many as 60% of nurses who work at night report poor sleep quality [9]. Such results are concerning because poor sleep quality increases the risk of medical errors and reduces concentration and overall work efficiency [10]. It was observed that when working night shifts, there is a 30% higher risk of work-related errors compared with working day shifts [11]. Nurses who work at night often report symptoms of insomnia and severe fatigue, which further compromises their alertness and productivity [10,11,12] and increases the risk of accidents and injuries at work [13]. Previous research has shown that most night shift nurses prefer to sleep at night during their days off. Among the identified sleep adjustment patterns, the nap proxy and sleep strategies were found to be associated with poorer adaptation to night shift work, including greater sleep disturbances and increased cardiovascular risks. These findings suggest that maladaptive coping strategies may exacerbate the negative health consequences of night shift schedules and highlight the importance of promoting healthier sleep–wake adjustment behaviors among nurses [14].

In the assessment of sleep quality, two main methodological groups of instruments are used: subjective and objective methods [15]. Subjective methods are based on self- assessment and include standardized questionnaires, sleep diaries, and interviews, which provide insight into individuals' perceptions of their sleep experience. Self-perception of sleep quality is challenging because no universally accepted gold standard exists. One of the most commonly used approaches is the application of standardized questionnaires, among which the Pittsburgh Sleep Quality Index (PSQI) stands out. The PSQI was developed in 1988 to provide a reliable and valid measure of sleep quality and distinguish between "good" and "poor" sleepers, which is practical for both subjects and clinicians [16].

Objective methods rely on measurement devices and laboratory procedures and assume that subjective judgement has minimal influence. Polysomnography [PSG] is the gold standard in sleep assessment because it allows for the most precise analysis of its structure, including non-rapid eye movement (NREM) and rapid eye movement (REM) sleep phases, and is based on the simultaneous recording of multiple physiological parameters. Although it provides very detailed data, PSG requires specialized laboratory conditions and is associated with high costs, which limits its application in long-term and field studies [17].

Actigraphy is a non-invasive method used to objectively assess sleep–wake patterns. It is based on the use of a fan accelerometer that records a person's body movements. By analyzing the rhythm and frequency of movements, it is possible to determine sleep duration and efficiency, its fragmentation, and the basic patterns of the circadian rhythm. Unlike PSG, actigraphy allows for the long-term monitoring of sleep in natural conditions, which has been proven to be practical in epidemiological and longitudinal studies. However, its precision is lower compared with PSG, particularly in distinguishing between different sleep stages and detecting brief awakenings [18,19].

Technological advances have enabled the development of commercial wearable devices, such as the Fitbit, Oura Ring, Garmin, or Apple Watch, which combine accelerometry with additional physiological signals, including heart rate, heart rate variability, oxygen saturation, and peripheral temperature. These devices have demonstrated satisfactory reliability in assessing total sleep duration, while their accuracy in differentiating sleep stages and detecting awakenings remains limited [20,21].

To date, no study in Croatia has compared subjective and objective assessments of sleep quality in nurses in the context of shift work. This study aims to fill the existing gap in the literature and contribute to our understanding of sleep quality in the nursing population. The aim of this study was to examine the differences in subjectively and objectively measured sleep quality in nurses in relation to shift work.

This study included 140 respondents, of whom 25 (17.9%) were men and 115 (82.1%) were women (Table 1). The median age of the respondents was 44 years, ranging from 20 to 64 years. A total of 67 (47.9%) respondents had a secondary education, and according to length of service, the least number of respondents, 12, had 6–10 years of service (8.6%). In total, 70 (50%) respondents worked shifts.

Nurses working rotating shifts and those working day shifts accumulated an equal total number of working hours during the measurement period (48 h), despite differences in shift length and number of working days. The distribution of years of nursing experience was comparable between the two groups (Table 2).

The respondents who worked rotating shifts were significantly younger than those who did not (median 40 years vs. 45 years) (Mann–Whitney U test, p = 0.04), while there were no significant differences in body mass index based on type of work (Table 3).

Subjective sleep quality was determined by answering the question of how the respondents would rate their sleep over the last month (Figure 2). The majority of respondents reported very good sleep over the past month 120 (85.7%), with few reporting bad 3 (2.1%) or very bad sleep 2 (1.4%). There was no significant difference in subjective sleep quality with respect to type of shift work (Fisher's exact test, p = 0.17).

There were no significant differences in sleep latency in relation to type of shift work (Table 4). A total of 29 (21%) of the respondents slept for more than seven hours a night, and 19 (14%) slept for less than five hours, with no significant difference in relation to shift work (χ² test, p = 0.16). It was observed that shift work significantly impairs sleep efficiency (Fisher's exact test, p = 0.002). Most respondents, 85 (61%) of them, reported 1–9 problems that caused them to wake up during the night or early in the morning, and only 1 (1%) respondent stated that they had no sleep disorders. There were no significant differences in the distribution of respondents according to sleep disturbance in relation to shift work (Fisher's exact test, p = 0.78). There were no significant differences in the use of sleep medications (Fisher's exact test, p = 0.50) and daytime sleepiness in relation to shift work (Fisher's exact test, p > 0.99) (Table 4).

The median subjective sleep quality was 0 (very good), ranging from 0 (very good) to 3 (very bad) (Table 5). There were no significant differences in the subjective sleep quality score in relation to shift work (Mann–Whitney U test, p = 0.27). Likewise, there were no significant differences in subjective sleep quality scores and in the total sleep scale scores in relation to shift work. Considering the total sleep scale values, all respondents are poor sleepers (score of 5 and above).

Respondents who work day shifts have significantly better sleep parameters compared with those who work rotating shifts (Table 6): they have significantly longer total sleep (median 6.4 vs. 5.5 h) (Mann–Whitney U test, p < 0.001), have a higher sleep score (77 vs. 73) (Mann–Whitney U test, p < 0.001), and have a longer duration of all sleep stages, including deep sleep (Mann–Whitney U test, p = 0.01), light sleep (Mann–Whitney U test, p < 0.001), and REM sleep phase (Mann–Whitney U test, p < 0.001).

Responders who worked rotating shifts took a significantly higher number of steps per day (median: 10,662 vs. 7295) (Mann–Whitney U test, p < 0.001) (Table 6).

Based on the sleep score results collected using the smartwatch, the majority of respondents, 104 (74.3%), had a moderate sleep score (Table 7). With regard to the sleep score values, it was observed that shift work was associated with a worse quality of sleep (Fisher's exact test, p < 0.001) objectively measured with the smartwatch.

The results of this study indicate an interesting and significant discrepancy between respondents' self-assessment of sleep quality, the standardized PSQI questionnaire, and objective data collected from a smartwatch (wearable technology). Three different data sources, namely self-assessment, PSQI, and the Fitbit Charge 3 smartwatch, led to different results.

Specifically, the vast majority of respondents rated their sleep as good or very good (96.4%), but according to the PSQI, 100% of respondents were classified as poor sleepers (PSQI > 5). No statistically significant difference was found between nurses who work rotating shifts and those who work exclusively in the daytime, neither according to the respondents' self-assessment nor according to the PSQI questionnaire, but it was observed that shift work significantly impairs the sleep efficiency of nurses who work rotating shifts.

These results are unexpected since the results of most studies suggest that shift work generally leads to poorer subjective sleep quality in nurses who work rotating shifts, which is in contrast to the results of this study [37,38,39,40,41,42]. Flo et al. reported that rotating shift work significantly increased respondents' ratings of poor sleep quality compared with those who engaged in fixed daytime work [37]. In a study of 510 healthcare workers in Saudi Arabia, the results indicated that healthcare workers working rotating shifts had significantly higher mean PSQI scores compared with those working only daytime shifts [38]. A study in Spain involving 635 nurses confirmed this pattern, reporting a mean PSQI score of 6.8, with significant differences between groups: nurses who worked night shifts had poorer sleep quality than those who worked daytime shifts [39]. A cross-sectional study of 513 nurses found that rotating shift work was significantly associated with poor sleep quality [40]. A study of 711 nurses in China found out that 90.1% of those working night shifts reported poor sleep quality, with work experience, education, quality of sleep compensation, and daily routine being the key factors associated with poorer sleep [41]. A meta-analysis conducted in China found that 39.2% of Chinese healthcare workers have poor sleep quality. Higher rates of sleep disorders are associated with female gender, lower PSQI scores, nursing occupation, and rotating shift work [42]. One possible explanation for this finding in this study is that a simple sleep questionnaire likely captures a general impression rather than the actual duration and structure of sleep. Healthcare workers may underestimate sleep problems; they may be trying to maintain an image of professional competence, or perhaps prolonged fatigue is becoming the "new normal".

Self-reported sleep quality showed a very optimistic picture, with 96.4% of respondents rating their sleep as good or very good. We believe that these findings suggest a positive bias and adaptation to chronically disrupted sleep patterns. It seems that nurses, due to their long-term demanding environment, have developed cognitive and emotional coping mechanisms that enable them to perceive their sleep as satisfactory, even though objective data suggest otherwise. Nurses working night shifts often adopt various coping strategies to mitigate the negative effects of rotating shift work on sleep quality. The most common strategies include creating favorable sleep conditions and behaviors, balancing rest and activity time, accepting irregular sleep patterns, and seeking social support [43]. These findings are consistent with previous research that indicated that rotating shift work significantly impairs sleep efficiency, as measured by the ratio of hours of sleep to time spent in bed. A likely explanation is that nurses working rotating shifts create favorable sleep conditions and behaviors and spend more time in bed trying to fall asleep due to irregular sleep patterns. In addition to these individual factors, shift work organization is also important. When a hospital implements favorable shift protocols, such as a limited number of consecutive night shifts and ensuring at least two days of rest after a night shift, circadian rhythm disturbances are milder and subjective perceptions of sleep quality are more favorable. Such a work organization was present in this study. Research from around the globe emphasizes that at least two consecutive days of rest are required for full recovery after working a night shift, and at least three days of rest are required after working two consecutive night shifts [44,45].

One possible explanation is that nurses who work day shifts also experience high levels of occupational stress, which in itself can negatively affect sleep quality. It is therefore possible that professional workload reduces differences between groups when subjective questionnaires are used, which can explain the high levels of stress and workload present in the nursing profession in general, regardless of the work regime [46,47]. Previous studies have also shown that nurses who work exclusively during the day may also have poor sleep quality, which is often associated with burnout [48].

An additional explanation may be found in the so-called "healthy worker effect" [49]. For instance, nurses who remain in rotating shift work for a long time represent a more resilient group, while those who find it more difficult to tolerate night shifts more often switch to day work or leave more demanding jobs. Also, the respondents who worked rotating shifts in this study were more active, taking significantly more steps per day. Such a selection may lead to an apparent equalization of subjective perceptions of sleep quality between groups, although objective measurements still show reduced sleep duration, particularly in terms of deep and REM sleep, which do not return to levels comparable to those of day-shift workers. Similar results have been reported by Huang et al., who found that the prevalence of poor sleep quality remains high, even among nurses who have stopped working night shifts (about 56%), while among those who continue to work at night, it is 62% [50]. A recent meta-analysis of studies published between 2000 and 2020 that assessed sleep quality using the Pittsburgh Sleep Quality Index (PSQI) reported significantly poorer sleep quality among nurses working rotating and fixed night shifts compared with those working fixed day shifts. These findings further support the robustness of PSQI as a widely used instrument for evaluating sleep disturbances in shift-working nursing populations [51].

In contrast to subjective measures, the objective sleep quality parameters used in this study clearly demonstrated the negative impact of shift work. Nurses working rotating shifts slept for about one hour less overall (5.5 h) than those who worked exclusively during the day (6.4 h), and all sleep stages were reported to be shortened in nurses working rotating shifts. Accordingly, their average sleep score was statistically significantly lower.

These results are consistent with the findings of most previous studies that have used objective wearable sleep measurement devices. Hafycz et al. used Fitbit smartwatches and found that after night shifts, subjects had the poorest sleep quality, with the least total, light, deep, and REM sleep compared with those who worked other shifts [52]. Developing upon Hafycz et al.'s study, in this study, nurses working rotating shifts also showed poor sleep quality, with even shorter durations of all sleep stages. Our findings are consistent with an Italian study conducted with a sample of 37 nurses who wore an actigraph device for five days to assess their daytime activity levels, nighttime sleep parameters, and daytime rest. In the aforementioned study, it was found that night shifts significantly impaired sleep duration compared with day shifts [53]. Similarly, a Canadian study by Korsiak et al. that included a large sample of 294 hospital workers who wore an actigraph device for one week showed that rotating shift work resulted in shorter and poorer sleep, especially after working night shifts, where shift workers slept for an average of 20–30 min less [54]. In our study, however, the difference was about one hour, indicating a more serious impact. The results of this study are consistent with a study of 64 hospital nurses, half of whom worked rotating shifts, whose sleep duration was measured over six consecutive days using a Fitbit Charge 3. Nurses working rotating day and night shifts had significantly shorter total sleep duration, longer sleep latency, and lower sleep efficiency compared with those working day shifts. Particularly unfavorable values were observed in nurses working three or more consecutive night shifts, confirming that the frequency and duration of night shifts further worsen sleep quality [55]. Unlike previous studies reporting poor subjective sleep quality among nurses, most participants in the present study rated their sleep as good or very good. This may be attributed to the typical shift schedule in our hospital, in which a single night shift is followed by two days off, potentially supporting better perceived sleep quality. A Polish study of 126 nurses reported that prolonged night and rotating shift work leads to circadian rhythm disruption, reduced sleep quality, and cumulative negative consequences for nurses [56].

More recent research has further expanded our understanding of the effect of night work by including the partners of healthcare workers. For example, a 2025 Japanese study involving 30 nurses and their partners who wore Fitbit devices for 14 days found that night work was significantly associated with poorer sleep quality. In addition, the presence of night shifts among nurses also disrupted the sleep of their spouses [57]. This shows that the negative effects of shift work go beyond the workers themselves to the family environment. In this context, rotating shift work and night work have multiple consequences for the physical, psychological, and social health of nurses. Given that the effects of shift work go beyond the individual and affect the family and social and organizational dynamics [58], it is necessary to design interventions that will address all these levels.

The results of this study show that there is no significant difference in the subjective assessment of sleep quality between nurses who work rotating shifts and those who only work day shifts. However, objective measurements using the Fitbit wearable device (Fitbit, Inc., San Francisco, CA, USA) show that rotating shift work is associated with poorer sleep quality. Nurses who worked rotating shifts slept less and had a lower total sleep score and a shorter duration of deep and REM sleep compared with respondents who work day shifts.

The obtained results indicate that assessing sleep in a subjective manner is not always a reliable indicator of real sleep quality. By combining the PSQI questionnaire and wearable devices that record the physiological indicators of sleep, a more realistic and complete picture of sleep habits and actual rest can be achieved.