title: Morningness-eveningness and daytime functioning in university students: the mediating role of sleep characteristics.
abstract: The aim of this study was to explore the mediating role of sleep characteristics in the relationship between morningness-eveningness and three different aspects of daytime functioning: daytime sleepiness, depressive mood and substance use in university students. A multiple mediator model was proposed with sleep debt, poor sleep quality and bedtime delay at weekends as parallel mediators in these relationships. We analysed the data of 1052 university students aged 18-25 years who completed a modified version of the School Sleep Habits Survey, which included questions on sleep and the Composite Scale of Morningness, Sleepiness Scale, Depressive Mood Scale and Substance Use Scale. Students with more pronounced eveningness reported greater daytime sleepiness, greater depressive mood and more frequent substance use, as well as greater sleep debt, poorer sleep quality and greater bedtime delay at weekends. Mediation analyses indicated that morningness-eveningness affected daytime sleepiness and substance use both directly and indirectly through all proposed sleep-related mediators. However, the effect of morningness-eveningness on depressive mood was entirely indirect and was accounted for more by poor sleep than by sleep debt or bedtime irregularity. In conclusion, there are multiple possible mechanisms through which morningness-eveningness affects daytime functioning in university students, and sleep characteristics are a significant mechanism. Sleep debt, poor sleep quality and bedtime irregularity can, to a significant extent, explain the feeling of daytime sleepiness and greater substance use in students with eveningness preferences. However, more depressed mood in the evening-orientated students is primarily a consequence of their poor sleep quality.
authors.affiliation: Institute for Medical Research and Occupational Health, Zagreb, Croatia.
authors.forename: Marija
authors.initials: M
authors.lastname: Bakotic
authors.affiliation: Institute for Medical Research and Occupational Health, Zagreb, Croatia.
authors.forename: Biserka
authors.initials: B
authors.lastname: Radosevic-Vidacek
authors.affiliation: Institute for Medical Research and Occupational Health, Zagreb, Croatia.|Department of Psychology, Centre for Croatian Studies, University of Zagreb, Zagreb, Croatia.
authors.forename: Adrijana
authors.initials: A
authors.lastname: Koscec Bjelajac
mesh_terms: D000293:Adolescent; D000328:Adult; D000339:Affect; D002940:Circadian Rhythm / Q000502:physiology*; D017523:Croatia / Q000453:epidemiology; D005260:Female; D006184:Habits; D006801:Humans; D008297:Male; D012890:Sleep / Q000502:physiology*; D012892:Sleep Deprivation / Q000453:epidemiology / Q000523:psychology; D007319:Sleep Initiation and Maintenance Disorders / Q000453:epidemiology / Q000523:psychology; D013334:Students / Q000523:psychology*; D019966:Substance-Related Disorders / Q000453:epidemiology; D011795:Surveys and Questionnaires; D014495:Universities; D055815:Young Adult
keywords: circadian preferences; parallel multiple mediation; young adults