Chronotype and environmental light exposure in a student population

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) spending 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.

Sex differences in the association between chronotype and risk of depression

“…Early light exposure advances the cycle while late light exposure delays the circadian phase 45 . Time spent outside, light dose, day length, and daily radiance were significant factors related to light exposure that showed a close association with chronotype 46 . However, items of light exposure were not included in KNHANES 2016, and we could not include light exposure in the present analyses.…”

Circadian Photoentrainment in Mice and Humans

“…Most recently, a study on university students from around the world showed that the late chronotypes (“owls”) were exposed to light in the evening (delaying light; see Figure 1 ) but experienced little light in the morning (advancing light). The net effect was to shift the body clock to a later time [ 208 ].…”

Light Regulation of Circadian Rhythms: Fact and Fiction and Design Implications

“…A recent study on university students from around the world showed that the late types ('owls') were exposed to light in the evening (delaying light) but experienced little light in the morning (advancing light). 5 The net effect was to shift the body clock to a later time. Another study from the USA examined sleep/wake timing in individuals after one week of maintaining daily routines of work, school, social activities and exposure to electrical lighting compared to one week of outdoor camping in tents and exposed to natural light.…”