No more nightlight? Even a dim room can keep kids from getting healthy sleep

BOULDER, Colo. — A child’s night light may do more than keep away the monsters hiding under their bed. A recent study by a team at the University of Colorado at Boulder suggests even slight exposure to dim light can disrupt a youngster’s sleep.

The research found any type of light exposure before bed can impact the production of a hormone called melatonin. Melatonin comes from the pineal gland in the brain and is a sign of your circadian rhythm — a 24-hour biological clock in charge of regulating when to sleep and when to stay awake — that it’s time to rest.

Melatonin is at its lowest in the daytime and accumulates around the evening when there’s less daylight. However, previous research has shown that light, whether natural or artificial, can disrupt your circadian rhythm by tricking the brain into thinking it’s still daytime. One way is that light slows the production of melatonin, delaying the body’s transition to sleep.

Sensitivity to light may be greater in children than adults, the researchers suggest. Children’s eyes are larger, meaning the pupils and transparent lenses can take in more light.

“Kids are not just little adults,” explains senior author Monique LeBourgeois, an associate professor of Integrative Physiology and one of the few researchers in the world to study the circadian biology of young children, in a university release. “This heightened sensitivity to light may make them even more susceptible to dysregulation of sleep and the circadian system.”

Light can suppress almost all melatonin production

The research team recruited 36 children between the ages of three to five for a nine-day study where children wore wrist monitors to track their sleep and light exposure at night. The first seven days recorded the children on a stable sleep schedule to normalize their circadian rhythms and adopt a pattern where melatonin levels increase at the same time each evening.

On the eighth day, the team transformed the children’s home into “caves” where they placed black plastic on the windows to dim the lights. They also took saliva samples from each child every half hour starting in the early afternoon until after bedtime to look at when the children’s biological night began and the level of melatonin at that time.

On the last day, every child played a game on a light table one hour before bedtime, in a similar position as someone looking at a lit-up phone or tablet. The light intensity varied from five lux to 5,000 lux (one lux is equivalent to the light from a candle three feet away).

Results show exposure to light suppressed melatonin levels by 70 to 99 percent in comparison to the previous night. Unlike adults, exposure to light made a bigger difference in melatonin suppression than brightness.

Specifically, lights at five to 40 lux — dimmer than the average room — suppressed melatonin by 78 percent. Moreover, melatonin production continued to be delayed for an additional 50 minutes after exposure to light.

“Together, our findings indicate that in preschool-aged children, exposure to light before bedtime, even at low intensities, results in robust and sustained melatonin suppression,” says Lauren Hartstein, a postdoctoral fellow in the Sleep and Development Lab at CU Boulder.

The research study is published in the Journal of Pineal Research.

About the Author

Jocelyn Solis-Moreira

Jocelyn is a New York-based science journalist whose work has appeared in Discover Magazine, Health, and Live Science, among other publications. She holds a Master’s of Science in Psychology with a concentration in behavioral neuroscience and a Bachelor’s of Science in integrative neuroscience from Binghamton University. Jocelyn has reported on several medical and science topics ranging from coronavirus news to the latest findings in women’s health.

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