Chronotype delay and sleep disturbances shaped by the Antarctic polar night

Abstract

Chronotype is a reliable biomarker for studying the influence of external zeitgebers on circadian entrainment. Assessment of chronotype variation in participants exposed to extreme photoperiods may be useful to investigate how changes in light-dark cycle modulate the circadian system. This study aimed to examine chronotype and sleep changes during a winter campaign at the Argentine Antarctic station Belgrano II. A sample of 82 men who overwintered in Antarctica completed the Munich Chronotype Questionnaire during March (daylight length: 18.6 h), May (daylight length: 2.8 h), July (daylight length: 0 h), September (daylight length: 14.5 h), November (daylight length: 24 h). The main results showed a decrease in sleep duration and a delay in chronotype and social jetlag during the polar night, highlighting the influence of social cues and the impact of the lack of natural light on circadian rhythms.

Figure 1

Circadian and sleep variations in Belgrano II. The curves in orange show the predicted values for Chronotype (A), Social Jetlag (B), Sleep duration on workdays (C), Sleep duration on work-free days (D), Total sleep on workdays (E), Total sleep on work-free days (F) during each measurement point. The grey lines show the mean and SEM of the respective variables. In the background, the photoperiod throughout the year is represented using three different colors: daylight is depicted in white, civil twilight in light grey and night in dark grey (https://www.timeanddate.com). The respective times throughout the day are shown on the right Y-axis, represented in clock time.

Figure 2

Day length at Belgrano II. Each point represents the average duration of natural sunlight throughout the year at Belgrano II Antarctic station. The curve illustrates the day length at each measurement point. Daylight is depicted by the color white, while the absence of natural light is shown in grey (https://www.timeanddate.com).