This study investigated the psychological dimension of morningness-eveningness in relation to subjective wellbeing and depression in emerging adults. Morningness-eveningness represents an individual preference for ideal sleep timing and preference for timing for physical and mental activities. Emerging adulthood is a period in which individuals gain more autonomy and flexibility over their sleep-wake schedule. In this period sleep patterns change and it is typical for emerging adults to stay up late and sleep late during their free days. Researchers refer to this difference in sleep time between work and free days as social jetlag. The aim of this research was to investigate the role of sleep quality and social jetlag as mediators in the relationship between morningness-eveningness and subjective wellbeing and depression. 362 emerging adults completed the Morningness – Eveningness Questionnaire Self – Assessment Version MEQ-SA, Mental Health Continuum – Short Form MHC-SF, The Pittsburgh Sleep Quality Index PSQI and The Center for Epidemiologic Studies Depression Scale CES-D. The results showed that eveningness predicts depression, social jetlag, lower sleep quality and lower subjective wellbeing significantly. Low sleep quality significantly predicts depression and lower wellbeing. Social jetlag, however, did not significantly predict depression or wellbeing. A subsequent mediator analysis showed that low sleep quality fully mediated the relationship between morningnes-eveningness and depression, indicating that higher levels of depression in people with evening preference may be attributed to their low sleep quality. On the contrary, low sleep quality in people with evening preference only partially mediated the relationship between morningness-eveningness and subjective well-being. This indicates that low quality of sleep contributes to lower level of subjective well-being. However, there likely are other sleep variables that will explain this relationship.
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