Bidirectional association between light exposure and sleep in adolescents.

Abstract

Sleep behaviour is controlled by both circadian and homeostatic influences. Changes in both factors are related to the delayed sleep timing observed in adolescence, which also generates restrictions in their sleep duration. In addition, the circadian factor explains part of the observed influence of light on sleep duration. We recorded 15high-school students for 23days (vacation: 11days; school term: 12days) using GENEactive accelerometers. We employed a repeated-measures analysis to explore the day-to-day bidirectional association between mean light exposure and sleep behaviour across a period with extreme variability in social pressures. Sleep onset was more than 30min earlier and sleep duration almost 20min longer when previous day light was 10 times more intense. Light intensity had a reduction of more than 20% as sleep ended 1hr later. Besides, sleep onset and offset were both later during vacation than on school days (almost 2hr and 4hr, respectively) and free days (almost 1hr, respectively). Therefore, sleep duration was almost 2hr longer on vacation and free days than on school days. On the other hand, light exposure intensity was twice as high during vacation days when adjusted by sleep timing. Insufficient sleep duration is a major problem for adolescents. Although we found that light exposure was associated with longer sleep duration, the influence of school start times was greater and ended up prevailing, which explained the short sleep durations observed on school days.