According to the updated data of the World Health Organization in 2017, 264 million people of all ages worldwide suffer from depression, among which the lifetime prevalence of depression in China is 6.9%, and the proportion of Chinese university students suffering from depression is as high as 23.66%. As a social group with high intelligence and pursuit, college students are the leading force to support the development and progress of society, and only with healthy and qualified physical and psychological quality can they take up all the important responsibilities in the future. The competition in contemporary society is getting fierce, the number of college graduates is increasing year by year, and the employment and life pressure of college students are high, so the mental health of college students deserves attention and attention. Many scholars in psychology, medicine, and education in China have researched the mental health status of college students. The survey results of Du Zhaoyun and Wang Keqin on 1579 college students show that the prevalence of mild depression is 42.1% and the prevalence of severe depression is 2.1%..According to statistics, the mental health problems of college students in China have been rising, with 28.23% of college students having mental disorders in the 1990s and 42% in recent years. According to the Ministry of Health, the mental health problems of modern college students are manifested as depression and anxiety, etc..
Medical school students are the training base for future medical workers and health administrators, so paying attention to the physical and mental health of medical school students has become the top priority for paying attention to the mental health of college students, which is the cornerstone of the future development of medical and health care.
Sleep is vital to human health, however, many people still suffer from sleep disorders, and many diseases are associated with poor sleep, such as cancer[4, 5], Heart Failure[6, 7], Depression, and general anxiety disorders, Schizophrenia, etc..For many college students, the transition to high school brings many new challenges, such as academic stress, smoking and drinking, physical activity, living environment, physical status, psychological status, work obligations, and new independence, which may provide the necessary stress for the development or worsening of sleep disorders, thus making sleep problems common among college students, More than half of college students suffer from poor sleep quality, which is more severe than the general population (according to statistics updated by the World Health Organization in 2017) and is detrimental to physical and mental health. Therefore, it can be asserted that poor sleep quality is becoming a considerable problem among university students.
Sleep disorders refer to abnormalities in the quantity or quality of sleep, or some clinical symptoms that occur during sleep. Insomnia is the most common sleep disorder in patients with depression, and this sleep disorder is considered an asymptomatic dimension of current depression. Sleep disturbance often lingers, and its persistence may represent a residual phase of the primary mood disorder. Alternatively, the presence of a sleep disorder may be a precursor or harbinger of depression that occurs later in life. Indeed, as part of an epidemiological catchment area study, Ford and Kamerowdiscover, persistent insomnia is associated with the development of the new major depressive disorder. Clinical and epidemiological investigations have shown that sleep disorders are closely associated with depression, highlighting the co-morbidity of sleep disorders and depression, including the concurrent co-morbidity model and the sequential co-morbidity model.In addition, it has been shown that as the level of depression increases, the total sleep quality and sleep quality component scores increase significantly, and on the other hand, depression levels are significantly higher in people with poor sleep quality than in people with good sleep quality. Changes in sleep architecture, such as those found in restricted sleep may also impair physiological function and increase depressive symptoms. In addition, research suggests that sleep, as an anti-inflammatory mechanism, may help maintain physical function later in life. Sleep disorders are common in college student populations, although the prevalence appears to be variable, perhaps in part due to methodological differences. NardoffIn a sample of 583 students, 13% reported clinically significant insomnia symptoms (according to the Insomnia Severity Index [ISI]) in the past 2 weeks. Gaultneydiscover, in a large sample of college students (N = 1, 845), 27% (n = 500) were at risk for sleep disorders (using the SLEEP-50, a tool validated for college students that measures sleep characteristics)). Other studies have reported a greater prevalence of sleep disorders. In one large study (N = 1, 125), the Pittsburgh Sleep Quality Index (PSQI) classified more than 60% of college students as poor sleepers. Finally, Singletondiscover, Of the 236 students who completed the interview survey, 79% reported going to bed after midnight, and only 24% reported getting enough sleep at night (i.e., at least 8.4 hours). In addition, there may be a cohort effect in that an even higher percentage of college students in recent generations self-reported dissatisfaction with their sleep.
Depression and anxiety disorders are among the most common disorders in the community and primary care. People with depression often have features of anxiety disorders, and people with anxiety disorders usually have depression as well. Both disorders may occur together and meet the criteria for both disorders, with approximately 85% of people with depression having significant anxiety and 90% of people with anxiety having depression.In the STAR*D study, 45%-46% of the 3787 outpatients with depression were considered to meet the criteria for anxiety depression. Näslund , illustrates the close relationship between anxiety and depression.
Anxiety and state-trait worry (WT) are closely related, but they are separate psychological concepts. Clinical studies have shown that high WT, especially high pathological worry, is an important clinical feature of anxiety disorders.Åkerstedt et al. (2007) found that people with higher levels of pre-bedtime WT were significantly less efficient sleepers compared to those with lower levels; people with higher levels of worry took longer to fall asleep and exhibited longer periods of light sleep. In addition, researchers noted that worry has been shown to differ from rumination in terms of its effect on sleep quality. The effect of state-trait worry on sleep quality is that it focuses on ongoing or future uncertain events, whereas rumination further exacerbates existing sleep problems by focusing on the "why", i.e., the cause of the problem, and people look back to the past to find an explanation. Anxiety includes state anxiety (S-AI), a description of momentary, fluctuating states of emotional feeling, and trait anxiety (T-AI), a tendency toward sustained, relatively stable trait anxiety. Frequent anxiety, in turn, consolidates anxiety traits, and individuals with higher levels of T-AI show more S-AI. In addition, individuals with high T-AI show evidence of attentional bias. They tend to pay attention to and even exaggerate negative emotional information, which directly correlates with their sleep quality. Christopher et al  argued that T-AI not only directly elicits high anxiety states but also modulates anxiety arousal by affecting the preattentive system, thus causing attentional bias. Among other things, T-AI plays an important role in evoking emotional arousal; the higher the T-AI of an individual, the more easily negative emotions are aroused and the poorer the quality of sleep.
Because the modern biomedical paradigm has not been transformed thoroughly enough, the singularity of education that focuses only on medical students' professional knowledge and not on the development of psychological and social knowledge is more serious; therefore, current research on the mental health of medical students is limited, with some focusing on the relationship between apprehension tendencies and sleep quality and the mediating role of state-anxiety. So far no study has analyzed one relationship between PSQI, STAI, and SDS. Therefore, the present study focused on the mediating role of traits between sleep and depression. Based on the purpose of our study, we made the following hypotheses.
1, there is a link between sleep disturbance and depression
2. state traits moderate the relationship between sleep disturbance and depression in college students