The current study is the first large-scale cross-sectional investigation to explore the prevalence of sleep disorders among medical students after the COVID-19 pandemic. Our main findings as follows: firstly, the incidence of sleep disorders among medical students after the COVID-19 pandemic is 82.3%; secondly, academic level, health condition, employment pressure, and pursuing clinical work after graduation influence sleep disorders; and finally, depression and high academic level are independent risk factors of sleep disorders among medical students.
The main finding is that the prevalence of sleep disorders is 82.3% among medical students after the COVID-19 pandemic. This result aligns with previous research [38]. For instance, a meta-analysis shows that sleep disorders are prevalent in the medical student population [38]. Another study found a 76% incidence of poor sleep quality among medical students [39]. However, the current study reveals a higher incidence of sleep disorders among medical students than earlier studies during COVID-19 [15, 17]. For example, a study in Greece found a sleep disorder incidence of 52.4% among medical students during the COVID-19 pandemic [15]. Additionally, a systematic review and meta-analysis reported a 52% incidence of sleep disorders among medical students during the COVID-19 pandemic [17]. These inconsistencies suggest differences in the prevalence of sleep disorders among medical students after and during the COVID-19 epidemic.
Furthermore, we found that the academic level influences sleep disorders among medical students after the COVID-19 pandemic. Previous studies have limited exploration of sleep disorder incidence among graduate students [40]. It is well known that there is a strong relationship between academic level and mental health [41]. Furthermore, it has been found that the higher the level of education, the higher the prevalence of sleep disorders [42]. For example, doctoral students had significantly higher levels of anxiety and sleep problems as well as depressive symptoms than master's students [43]. In addition, one study found that approximately 83% of graduate students experienced sleep disorders during the COVID-19 pandemic [40]. Our findings provide new literature on the relationship between academic levels and sleep disorders.
Another main finding of our study is that depression is an independent risk factor for sleep disorders among medical students after the COVID-19 pandemic. Depression is prevalent, costly, debilitating, and associated with an increased risk of suicide [44–46]. There is a close relationship between depression and sleep disorders [47, 48]. Most sleep disorders patients experience depressive episodes, and higher levels of depression are associated with an increased incidence of sleep disorders [49]. Hence, the relationship between depression and sleep disorders may be bidirectional [47, 48]. For instance, a meta-analysis found a positive correlation between depression and sleep disorders [50]. Studies have shown a higher incidence of depression in patients with sleep disorders [49]. The reasons of depression affects sleep disorders include: Firstly, Patients with depression have reduced circadian rhythm amplitude, and various treatments for depression have been shown to affect circadian rhythms [51]. Secondly, severe depressive disorders are associated with functional impairments in the structural network regulating rapid eye movement (REM) sleep [52]. Finally, the medial prefrontal cortex (mPFC) is a crucial region regulating depression and sleep, and significant changes in neural activity in the mPFC subregions of depression patients have been observed [53].
Our regression model reveals that anxiety is a factor influencing sleep disorders among medical students after the COVID-19 pandemic, consistent with previous research results [54, 55]. For example, research indicates that higher levels of anxiety are associated with a higher incidence of sleep disorders [56]. A meta-analysis also found a positive correlation between anxiety levels and sleep disorders [57]. However, when we include depression in the regression model, anxiety does not impact the sleep disorders of medical students. We hypothesize that depression has a more significant influence on sleep disorders among medical students than anxiety. Indeed, the relationship between depression, anxiety, and sleep disorders may be complex [58–61]. Therefore, further research is needed to systematically elucidate the relationship between depression, anxiety, and sleep disorders.
It is noteworthy that, before initiating this study, we predicted that infecting COVID-19 would affect the sleep disorders of medical students. Surprisingly, our study results indicate no difference in the incidence of sleep disorders among medical students infected once, more than two times, or not at all with COVID-19. This result may be attributed to China being one of the earliest countries to commence global COVID-19 vaccination campaigns, leading to a significant decline in COVID-19-related mortality rates [62]. Previous research suggests that repeated COVID-19 infections further increase the risks of death, hospitalization, and sequelae[63]. However, no research exists exploring the impact of repeated infections and the number of infections on sleep disorders. Therefore, more studies are needed to investigate the effects of COVID-19 infection on sleep.
Despite providing valuable insights, our current study has limitations that must be acknowledged. Firstly, the cross-sectional study limits our detailed understanding of how COVID-19 affects sleep disorders. Future research should employ longitudinal studies to understand the temporal effects of these results. Secondly, due to the online survey design, most studies used self-administered questionnaires without clinical diagnostic confirmation. However, all included studies used validated screening tools such as the SDS, SAS, and PSQI. Therefore, future research is recommended to use rigorous clinical diagnosis to confirm our results. Thirdly, the questionnaire did not include whether participants were isolated during the COVID-19 pandemic, and it remains unclear whether this would affect sleep disorders. Finally, the current study only assessed medical students in China, and generalizing the results to the entire medical student population may be challenging.
In conclusion, the incidence of sleep disorders is high among medical students after the COVID-19 pandemic. Additionally, depression and high academic levels are independent risk factors for sleep disorders among medical students. Thus, to reduce the incidence of sleep disorders among medical students after the COVID-19 pandemic, targeted intervention strategies must be developed.