Estimation of sleep shortening and sleep phase advancing in response to advancing risetimes on weekdays.

Since the circadian clocks cannot directly respond to the signals of social clocks, earlier risetimes on weekdays lead to loss of certain amount of sleep. However, these clocks can partly reduce this loss by advancing sleep phase due to advancing the pattern of 24-h exposure to light caused by earlier risetimes. In an study, a model of sleep-wake regulation was applied to show that the difference between earlier and later weekday risers in weekday risetime is equal to the sum of differences between them in sleep loss and sleep phase advance that can be measured as their differences in weekend-weekday gap in risetime and in weekend risetimes, respectively. Such differences in sleep loss and sleep phase advance were estimated from bed- and risetimes self-reported for weekdays and weekends by 4940 university students and lecturers subdivided into subsamples with different weekday risetimes and chronotypes. We also estimated, for these subsamples, the percentages of weekday sleep insufficiency and circadian misalignment determined as a less than 6 hours in bed on weekdays and a larger than 3-h weekend-weekday gap in risetime, respectively. Additionally, advance phase shifts of the circadian clocks were predicted by model-based simulations of self-reported sleep times.