Medical training was frequently associated with changes in sleep/wake cycle due to work stress, extended working hours, and night shifts [12, 18]. The current study revealed that the quality of sleep was negatively impacted during residency, as 96.7% of the participating residents had poor sleep quality. Their score in PSQI was 10.4 ± 2.5 which indicated higher disturbance of sleep. The results were in accordance with previous studies [19,20,21,22].
We found average 3 h drop of sleep time in the participating residents compared to their sleep duration prior to start of training. Linear regression analysis suggests a predictive association between number of sleep hours before residency and sleep quality as assessed by PSQI. In a prospective study of sleep in first year residents [23], following up night sleep duration in fresh residents over 9 months showed statistically significant decline of their baseline sleep and increase of PSQI score.
Furthermore, in the present study, although residents of medicine-related specialties manifested slightly poorer sleep as they scored higher on PSQI (10.6 ± 2.3) than surgically oriented specialties (10.1 ± 2.6), no statistically significant difference among different specialties was detected (p = 0.615). This agrees with Tür et al.’s study [21] which failed to find a significant difference in the average PSQI values between the emergency, internal medicine physicians, and surgeons.
In contrast, Lashkaripour et al. study [20] spotted statistically significant better sleep in radiologists and ophthalmologists compared to other specialties (p < 0.05), while Esen et al. [24] found that surgeon demonstrated the poorest sleep (p = 0.015). In Alsaif’s study [22], 96% of anesthesiologists demonstrated poor sleep quality compared to 68.7% of pathology residents.
Our study resembled the first two studies [20, 24] in that radiologists had the relatively best sleep among included specialties (mean ± SD = 9.3 ± 3.1) and general surgeon battled poorest sleep (mean ± SD = 11.5 ± 1.7) which was matched with the pediatricians’ score and (mean ± SD = 11.5 ± 2.1) in the current research pediatricians. However, the variance was not significant.
In the same context, the only subscale that showed statistically significant difference between the included specialties was sleep duration (p = 0.045*). General surgery and geriatrics residents were the uppermost regarding sleep duration score (mean ± SD = 2.5 ± 1.0 and 2.3 ± 0.9 consecutively), opposed to clinical pathologists who scored the lowermost (mean ± SD = 0.4 ± 0.5).
The quality of night shifts in surgery words and departments caring for patient of highly vulnerable patients in extreme age might explain the results. In contrast, radiologists and clinical pathologists worked under less stressful circumstance and they did not need to take major decisions related to patients’ lives.
Habitual sleep efficiency and daytime dysfunction were the highest scores among the PSQI parameters in our sample. All residents scored an average of 2.1 ± 0.8 in daytime dysfunction with highest daytime dysfunction among medically oriented residents especially pediatricians.
Many studies associated poor sleep quality to decline in second day functioning [3, 25, 26]. Accumulating research negatively correlated long shifts and lack of regular rest to the performance of medical residents, though results were controversial and not conclusive [10, 27,28,29].
The present study found statistically significant positive correlations between the number of monthly shifts and sleep duration (r = 0.205, p = 0.012), day dysfunction (r = 0.258, p = < 0.001**), subjective sleep quality (r = 0.208, p = 0.011), and medication intake (r = 0.176, p = 0.031*) reflecting the degree of disturbance developed especially with frequent shifts. In prior research, extended shifts negatively impacted sleep, alertness, performance, increased errors [30, 31], and was linked to wide range of physical impairments [30]. Disruption of circadian rhythm led to biological imbalance such as chronic sleep disturbance and was associated with a variety of health risks [32].
On the other hand, number of monthly shifts was inversely correlated to sleep latency (r = − 0.236, p = 0.004*), intake of sedating medications by residents who work more shifts could be the cause of reduced sleep latency.
There was a significant negative correlation between the number of days off and daytime dysfunction (r = −0.207, p = 0.011*), indicating the detrimental effect of lack of rest on the residents’ performance. Further to that, the number of days off during residency was one of the predictive factors of the PSQI score as confirmed by linear regression analysis. Previous studies recommended that sufficient time off duty was mandatory for recovery sleep especially after longer shifts [3] and improve quality of performance [28, 33] and reduce errors [34].
However, other studies did not detect a significant effect of restriction of duty hours on the burnout, performance, and wellbeing of the residents [13]. Interestingly, the number of days off showed positive correlation with sleep latency and sleep disturbance (r = 0.164, p = 0.045* and r = 0.205, p = 0.012* correspondingly). In comparison, earlier studies showed unexpected stability [35] or decline in sleep hours in spite of restriction of shift durations [36].
In consistence with number of former studies that found advanced years of training a risk factor for subjective sleep disturbance and sleep dissatisfaction [19, 37] or related to decline of total sleep quality [20, 38], our results revealed significant positive correlation between duration of residency and sleep latency (r = 0.185, p = 0.024*) that denotes decline in sleep amount and poor sleep efficiency and quality with advance of years of residency.
Stress was associated with detrimental effects on sleep [39, 40]; therefore, we agree with Lashkaripour et al. [20] that the increasing occupational, economic and social responsibilities could contribute to the poor sleep. Moreover, the stress of the final Master’s degree exams and the thesis defense which happen during the last year of residency add another trigger of stress during that period of training.
Study limitations
This study has some limitations. First, the measurement of sleep disturbance was subjective as it was self-reported, which might made it prone to recall bias. However, we tried to overcome that by using a validated and widely used scale (PSQI). Secondly, our study was a cross-sectional study which did not allow for inferences on cause and effect. Thirdly, generalization of our results would be difficult, since we conducted this study at a single center.
Therefore, future longitudinal multicenter studies are suggested to evaluate the possible causal relationship between residency and poor sleep quality in individual specialties who carry out inpatient and outpatient duties. Moreover, a special focus on organizational characteristics of the jobs is required as a step for development of physician’s wellness-oriented work conditions.
