Chronotype and environmental light exposure in a student population

Kate Porcheret, Lucien Wald, Lin Fritschi, Menno P. Gerkema, Margaretha Gordijn, Martha Merrow, Shanta M.W. Rajaratnam, Daniel Rock, Tracey Sletten, Guy Warman, Katharina Wulff, Till Roenneberg, Russell Foster

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Abstract

In humans and most other species, changes in the intensity and duration of light provide a critical set of signals for the synchronisation of the circadian system to the astronomical day. The timing of activity within the 24 h day defines an individual’s chronotype, i.e. morning, intermediate or evening type. The aim of this study was to investigate the associations between environmental light
exposure, due to geographical location, on the chronotype of university students. Over 6 000 university students from cities in the Northern Hemisphere (Oxford, Munich and Groningen) and Southern Hemisphere (Perth, Melbourne and Auckland) completed the Munich ChronoType Questionnaire. In parallel, light measures (daily irradiance, timing of sunrise and sunset) were compiled from satellite or ground stations at each of these locations. Our data shows that later mid-sleep point on free days (corrected for oversleep on weekends MFSsc) is associated with (i) residing further from the equator, (ii) a later sunset, (iii) pending more time outside and (iv) waking from sleep significantly after sunrise. However, surprisingly, MSFsc did not correlate with daily light intensity at the different geographical locations. Although these findings appear to contradict earlier studies suggesting that in the wider population increased light exposure is associated with an earlier chronotype, our findings are derived exclusively from a student population aged between 17 and 26 years. We therefore suggest that the age and occupation of our population increase the likelihood that these individuals will experience relatively little light exposure in the morning whilst encountering more light exposure later in the day, when light has a delaying effect upon the circadian system.
Original languageEnglish
Pages (from-to)1365-1374
Number of pages10
JournalChronobiology International
Volume35
Issue number10
Early online date18-Jun-2018
DOIs
Publication statusPublished - 2018

Keywords

  • Chronotype
  • light
  • MCTQ
  • Students
  • daily irradiance

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