As any parent can tell you, when the long days of summer strike, it can be nearly impossible to get kids to bed on time. Now, a study presented at "SLEEP 2016: 30th Anniversary Meeting of the Associated Professional Sleep Societies" may offer insight into this problem. Researchers found that exposing very young children to bright light in the evening suppressed their melatonin, a hormone that controls the sleep–wake cycle. For the first five days of the seven day trial, ten preschool-aged children were assigned to a stable sleep schedule, which was verified by sleep monitors worn on their wrists. On the afternoon of the sixth day, the children entered a dimly lit environment; then, one hour later, researchers began collecting saliva samples from the children every 20 to 30 minutes until 50 minutes after their scheduled bedtime. On the seventh day, the children remained in a dimly lit environment, staying there until one hour before their bedtime. They were then moved to a brightly lit environment for one hour before heading back to the dimly lit environment. Researchers took saliva samples before, during, and after the bright-light exposure. After comparing samples from day seven to those taken during similar times on day six, researchers found that:
One hour of bright light in the evening suppressed the children’s melatonin secretion by about 88%.
Melatonin levels remained suppressed when the last saliva sample was collected, 50 minutes after the children left the brightly lit environment.
In seven of the ten children, melatonin levels were still less than 50% of their baseline dim light levels at the time of the last sample.
These findings suggest that bright light may interfere with children’s ability to fall asleep by suppressing their melatonin production for at least 50 minutes. This study doesn’t tell us how long melatonin production is suppressed after bright light exposure, but other evidence suggests that excessive light exposure from electronic screens may be associated with lasting problems with melatonin suppression and sleep problems in children and teens. So, keeping the lights low and reducing screen time to limit bright light exposure before bedtime may help your kids get to sleep on time and support healthy melatonin production.