Day-to-Day Variation of Subjective Sleep Quality and Emotional States Among Healthy University Students-a 1-Week Prospective Study

In spite of the apparently bidirectional relationship between daytime emotions and nocturnal sleep quality, relatively few studies have examined the day-to-day co-variation of daytime emotional states and sleep quality. In order to address this issue, we used a 7-day prospective design allowing for the simultaneous investigation of the bidirectional link between sleep quality and affective states. Seventy-five healthy university students completed a daily log during 7 days, reporting subjective sleep quality after their final morning awakenings. Eight hours later, they completed the Positive and Negative Affect Schedule measuring daytime affective states. Multilevel modeling was applied in order to examine level 1 (day-to-day co-variation of sleep quality and affective states within individuals) as well as level 2 (averaged between-subjects) effects. Individuals reporting poor sleep quality (on average) were characterized by lower positive and higher negative affect during daytime. Similarly, higher positive and lower negative affect (on average) predicted better subjective sleep quality during the assessment period. Moreover, daily ratings of positive and negative affect were related to the subjective sleep quality of the preceding night: On occasions in which participants reported poor (below average) sleep quality, they also reported lower positive and higher negative affect during the day. Nevertheless, daytime positive and negative affective states did not predict subsequent sleep quality ratings. These findings suggest daily dynamic associations between subjective sleep quality and next day's emotional states in a group of healthy individuals, while in the inverse, the co-variation between daytime affective states and subsequent sleep quality was not supported.