Breakpoints of time in bed, midpoint of sleep, and social jetlag from infancy to early adulthood

Objectives: The present study investigated sleep duration and sleep timing from infancy to early adulthood. Methods: A cross-sectional survey study of N = 18,323 participants (9004 female) from 0 to 25 years (M = 12.36; SD = 5.76) from kindergartens, schools and universities in SW Germany. Participants reported their usual bedtimes and rise times on weekdays/weekends. Time in bed (TIB), the midpoint of sleep, and social jetlag were calculated from these four clock times. Results: Weekday rise times were progressively earlier until the age of 17 years, while weekend rise times contrarily were later. As a consequence, TIB during the week was progressively shorter until the age of 16 years. The midpoint of sleep (MSFsc) was increasingly later until it reached a plateau at 17 years. Social jetlag increased until 16 years to 3: 18 h. Gender differences were small for sleep duration/chronotype with males sleeping less and later than girls and non-significant for social jetlag. A regression with two breakpoints explained variability in sleep duration and sleep timing by age (45-61% explained variance) better than a regression with one breakpoint (44-59%), linear regression (25-54%) or polynomial regression (43-60%). Conclusions: The age around 16-17 years can be considered a remarkable breakpoint when sleep behavior significantly changes back towards slightly longer sleep, less socially jetlagged behavior, and the increase in eveningness is then stopped but not reversed. A somewhat softer breakpoint is identified around 5-7 years when the rapid changes in sleep behavior initiate. (c) 2019 Elsevier B. V. All rights reserved.