大学生是日常压力与睡眠问题较为突出的群体。对于大学新生而言，从高中迈入大学是他们成长发展过程中一个重要的转折阶段，在新的学习与生活环境中，大学新生往往需要面临来自学业发展、环境适应等多方面的压力与挑战。国内外调查数据显示，大学新生在失眠、睡眠质量低下等问题方面属于高危人群，睡眠质量的下降可能对大学生学业、社会适应及身心发展带来一定的消极影响。因此，大学新生群体内的压力与睡眠问题更加值得关注。反刍思维是压力-睡眠模型中重要的认知性中介因素，是日常压力负面效应的延续过程。本研究将反刍视为状态性变量来观察每日变化，并探究其在每日层面的日常压力与睡眠质量关系间的中介作用。在日常压力作用过程中，压力应激系统也是重要的生理环节，而压力应激系统分泌的皮质醇日常节律是反映压力应激系统功能的常用指标。基于已有研究，本研究在压力-睡眠模型中纳入压力应激系统，将日常皮质醇分泌总量视为个体特质变量，探讨其在睡眠影响路径中的调节作用。

本研究选取101名北京某大学新生（18.10±0.70岁）为被试，采用日记法的方式，通过电子问卷对大学新生的日常压力、睡眠质量和反刍等变量进行每日测量，获得共八天的有效数据；并选择连续三天的工作日采集日常唾液皮质醇样本，在每天早上刚睡醒、醒后30分钟和睡前各收集1次唾液样本，利用梯形法则计算皮质醇当天随时间变化的曲线下面积以计算个体日常皮质醇分泌情况。

多层线性模型结果显示：（1）在控制了咖啡因摄入、睡前手机使用、前一日的睡眠状况后，大学新生当日日常压力和前日日常压力对睡眠质量的直接作用均不显著。（2）针对反刍的中介效应，在同一天中，日常压力-反刍-睡眠的中介路径显著，且为完全中介，即当日日常压力能通过增加反刍从而增加睡眠问题（即睡眠质量更差）；在隔天的溢出效应模型中，前日压力-当日反刍-当日睡眠及前日压力-前日反刍-当日睡眠两条中介路径均为边缘显著。（3）对于日常皮质醇的调节效应而言，日常皮质醇显著地调节了同一天中日常压力-反刍-睡眠中介模型中的反刍-睡眠路径，且日常皮质醇较高的个体中反刍显著地正向影响睡眠问题，而日常皮质醇较低的个体中反刍对睡眠问题的预测作用不显著。在两个前日的日常压力模型中，日常皮质醇对反刍-睡眠的调节作用均为边缘显著。

本研究从微观动态视角出发，采用日记法问卷测查和生理皮质醇指标采集相结合的方式，考察了大学新生日常压力对睡眠的当天影响以及溢出效应，从认知层面（反刍）和生理层面（日常皮质醇）较为全面细致地探讨了大学新生群体日常压力对睡眠的影响机制。研究结论从微观日记层面拓展了压力与睡眠的潜在关联，并建立了涉及压力生理系统、认知过程的压力-睡眠关系模型，丰富了睡眠相关研究结果。该结论也为大学新生压力、睡眠问题的鉴别和干预提供了一定的思路和理论依据。

College students are a group with prominent daily stress and sleep problems, and the first year in college is especially crucial for future development. During the period, students are facing massive adaptive challenges in studying and daily life. According to surveys in many countries, first-year college students is most susceptible to insomnia and poor sleep quality. Therefore, in first-year college students, the relationship between daily stress and sleep quality at the day-to-day level is worth exploring. Rumination is a cognitive mediating factor in stress-sleep models, it prolongs the activation of negative effect from daily stressors. We regraded rumination as a state variable and observed its daily variation, thus explored its potential mediation effect on the relationship between daily stress and sleep quality. In the process of dialy stress affect sleep, stress response system is a essential physiological system, and the function of the system is often indicated by its product, cortisol, and the daily rhytem of cortisol. Based on existing research results, we investigated if daily cortisol as an individual trait could moderate the effect path of sleep quality.

In this study, 101 first-year college students from a university in Beijing were selected as subjects. Daily stress, sleep quality (PSQI was used, a higher score indicates more sleep problems), and rumination was recorded for a total of 8 days using a daily diary method. At the same time, the subjects' daily cortisol rhythm profiles were measured in 3 consecutive days. The cortisol levels were assessed at three time points in a day: morning awakening, 30 minutes after awakening, before sleep; and the daily cortisol was calculated by the area-under-curve (AUC) method.

We establish a multilevel linear model to explore their relationship. The results showed that: (1) After controlling caffeine intake, devices use before sleep and sleep quality of the previous day, neither the daily pressure of the day nor the daily pressure of the previous day significantly affected sleep quality. (2) Regarding the mediating effect of rumination, the full-mediation path of daily stress-rumination-sleep (same day) is significant. That is, the daily stress of the day could increase sleep problems by increasing rumination. The two mediation paths referred to as the previous day's daily stress were both marginal and significant. (3) As for the moderate effect of daily cortisol, daily cortisol significantly moderated the rumination-sleep path of the same-day stress-rumination-sleep model. Rumination in individuals with high daily cortisol profiles had a significant positive effect on sleep problems. The predictive effect of rumination on sleep problems in individuals with low daily cortisol profiles is not significant. In the two models of the previous-day stress, daily cortisol's moderate effect on the rumination-sleep path is marginally significant.

From the day-to-day dynamic perspective, the current study combined daily diaries and cortisol collection to investigate the impact of daily stress on sleep and the overflow effect on first-year college students. The study comprehensively explored the impact mechanism of daily stress on sleep from the cognitive level (rumination) and physiological level (daily Cortisol). The results expanded the relationship between stress and sleep from the micro-diary level, and establishes a stress-sleep relationship model involving physiological systems and cognitive processes, which enriches the results of sleep-related research. This conclusion also provides implications and theoretical basis for the identification and intervention of college students’ stress and sleep problems.