0252 Light Exposure Patterns and Sleep/Circadian Timing in Preschool-Aged Children

Abstract Introduction Young children (for whom earlier bedtimes are developmentally appropriate) are increasingly exposed to less bright, natural light during the day, and more artificial light at night. This can impact their sleep and overall health. Although it is known that nighttime light exposure can influence sleep and circadian timing in this age group, little is known about the impacts of daytime light exposure patterns. Methods Data were collected from 49 healthy, good-sleeping children aged 3.3 to 6.0 years (55.1% female). Children adhered to a consistent parent-selected sleep schedule for 7 days. They then completed an in-home dim-light melatonin onset (DLMO) assessment. Light exposure (lux) and sleep timing were assessed via wrist-worn actigraphy. Results Later mean timing of exposure to light greater than 10, 100, and 1000 lux were associated with later DLMO, bedtime, sleep onset, and sleep offset (all p≤0.001). However, when controlling for bedtime, the relationship between mean light timing and circadian phase was no longer significant. Longer exposure to bright light (1000 lux) was associated with earlier bedtime (p=0.01), sleep onset (p=0.03), and sleep offset (p=0.008). Greater light exposure 120- and 60-min before bedtime was also associated with earlier bedtime, sleep onset, and sleep offset. However, exposure to brighter light levels throughout the day (p=0.02), in the afternoon from 12:00 to 18:00 (p=0.005), and 180-min before bedtime (p=0.006), as well as longer exposure to light levels over 100 lux (p=0.03) and 1000 lux (p=0.02), were all associated with worse sleep efficiency. Conclusion Later average light exposure was associated with later DLMO and sleep timing, largely because of later bedtimes. However, children who went to bed early often had more light exposure 1-2 hours before bedtime, likely because they are going to bed shortly after sunset. Light exposure patterns also impacted sleep quality. These data suggest that age-appropriate earlier bedtimes in preschoolers may require different recommendations about light exposure before bed than older age groups. Future studies can look at the timing of light exposure as a strategy for improving early sleep health in the context of developmentally early sleep schedules. Support (if any) Data collection supported by F32-HD103390; R01-HD087707; T32-HL149646.