Circadian typology and implications for adolescent sleep health. Results from a large, cross-sectional, school-based study

Linn Nyjordet Evanger,Bjørn Bjorvatn,Michael Gradisar,Børge Sivertsen,Ståle Pallesen,Ingvild West Saxvig,Mari Hysing

doi:10.1016/j.sleep.2021.04.020

Abstract

Study objectivesTo investigate circadian typology in a large, representative sample of Norwegian adolescents, and its implications for sleep health. MethodsThe sample included 3920 1st year high school students aged 16–17 years. Respondents completed a web-based survey, including the short version of the Horne-Ostberg Morningness-Eveningness Questionnaire (rMEQ), the Munich Chronotype Questionnaire (MCTQ) and items on sleep-related behaviors (eg electronic media usage in bed, consumption of caffeinated beverages), sleep beliefs and daytime sleepiness. Data were analyzed using one-way ANOVAs and Chi-squared tests. ResultsIn all, 7.8% were categorized as morning, 52.3% as intermediate and 39.9% as evening types, respectively. Evening types had later sleep timing, longer sleep latency, more social jetlag and shorter school day sleep duration than morning types, with intermediate types displaying a sleep pattern between these two extremes. None of the circadian types met the minimum recommended amount of sleep on school nights (ie 8+ hours), and only morning types had a mean sleep duration of 7+ hours (7:19 h, nearly 1 h more than evening types who slept 6:20 h, p < 0.001). Evening types reported more use of electronic media in bed, more consumption of caffeinated beverages and more daytime sleepiness than the other circadian types. They were also less satisfied with their school day sleep duration and perceived it more difficult to change their sleep pattern. ConclusionsResults from this study suggest that eveningness represents a sleep health challenge for older adolescents.

Highlights

Circadian typology reflects the chronobiological phenotypes that arise from individual variations in circadian timing
Using the short version of the Morningness-Eveningness Questionnaire [1,12], Urban and colleagues found a distribution of circadian types amounting to about 30% morning and 20% evening types among Hungarian adolescents [13], whereas Li and colleagues found a distribution of circadian types closer to 10% morning and 20% evening types among adolescents in Hong Kong [14]
39.9% of the respondents were categorized as evening types whereas 52.3% were categorized as intermediate types and only 7.8% were categorized as morning types

Summary

Introduction

Circadian typology reflects the chronobiological phenotypes that arise from individual variations in circadian timing. Whereas the distribution of circadian types is about 20% morning, 60% intermediate and 20% evening types in the general population [3], a “Sleep in America” poll found 15 years ago that 56% of adolescents from 6th to 12th grade considered themselves “night owls” (zevening type) [10]. This poll, did not include a validated questionnaire on circadian typology, and it was conducted prior to the introduction of smartphones [11]. There is a need for studies addressing the distribution of circadian typology in large and age-specific, population-based samples, using validated questionnaires with predetermined cut-off criteria enabling comparison across studies

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