Sleep timing regulates mood: A multilevel-EEG study of daily life.

OBJECTIVES: Sleep and mood are homeostatically regulated systems essential for mental and physical health. Understanding how sleep timing and mood dynamically influence each other, and which individual traits moderate this coupling, can clarify mechanisms of mood regulation. Our objective was to examine bidirectional associations between sleep and daily mood under naturalistic conditions using objective sleep measurements and to identify personality and psychiatric traits that moderate these relationships. METHODS: Data came from the Budapest Sleep, Experiences and Traits Study, a 7-day observational study of 258 healthy adults (1712 nights). Objective sleep was recorded using Dreem2 EEG headbands, and subjective sleep quality was assessed by the Groningen Sleep Quality Scale. Daily mood was measured with the Positive and Negative Affect Schedule. Bidirectional multilevel models tested within-person associations between affect and sleep, while random slopes models examined individual differences. RESULTS: A robust negative feedback loop emerged between sleep timing and positive affect: higher evening positive affect predicted later sleep onset (r= 0.13, P<.001), while later sleep onset predicted lower next-day positive affect (r= -0.17, P<.001). This bidirectional link was absent for negative affect and objective sleep quality. Trait activity (r = -0.21), extraversion (r = -0.29), and conscientiousness (r = -0.19) amplified the effect, whereas neuroticism (r = 0.17) and alexithymia (r = 0.18) attenuated it. CONCLUSIONS: Sleep timing, rather than sleep quality, plays a central role in daily mood regulation through a homeostatic feedback mechanism. Personality and affective traits shape this loop, highlighting sleep timing as a potential target for mood stabilization.