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Light exposure before bedtime negatively impacts young children's sleep, study finds

Experts say even dim light can affect kids' quality of sleep

Child using phone at night in bed
Photo (c) Donald Iain Smith - Getty Images
Several studies have highlighted the ways that screens can negatively impact kids’ sleeping habits. Now, researchers from the University of Colorado at Boulder explored how even minimal light exposure may be detrimental to kids’ sleep

According to their findings, dim lighting before bedtime may affect preschoolers’ production of melatonin and disrupt their regular sleeping patterns. 

“Our previous work showed that one, fairly high intensity of bright light before bedtime dampens melatonin levels by about 90% in young children,” said researcher Lauren Hartstein. “With this study, we were very surprised to find high melatonin suppression across all intensities of light, even dim ones.” 

Keeping lights off near bedtime

For the study, the researchers had 36 children between the ages of three and five participate in a nine-day experiment. The children stayed on a strict sleeping schedule for the first seven nights; this allowed them to develop stable melatonin levels. On the eighth night, the kids’ rooms were transformed to be completely dark, and they had their saliva sampled every half hour from noon through bedtime. On the last night, the kids played on a light table an hour before bedtime. Each night of the study, the kids wore a watch that tracked their light exposure and sleep. 

The researchers learned that exposure to the light from the table significantly affected the children’s ability to produce melatonin. Compared to the second to last night of the experiment when the children’s rooms were darkened, the light from the table suppressed melatonin production anywhere from 70% to 99%. 

The researchers tested out different brightness levels on the last night of the study when the children were playing on the table. Even for children who had the tablets set to the dimmest levels, their melatonin production dropped by nearly 80%. For half of these kids, this light exposure before bed halted their melatonin production for the next hour. 

“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,” said Hartstein.  

Adopting healthy bedtime habits

From a biological perspective, the researchers explained that children’s eyes are more susceptible to light because their pupils are larger than adults’ pupils. This can certainly play a role when it comes to light exposure before bedtime. 

While it’s nearly impossible for parents to eliminate all forms of light for their kids before going to sleep, the researchers hope this study helps inform families about the things they can adjust to help encourage healthy sleep.

“Kids are not just little adults,” said researcher Monique LeBourgeois. “This heightened sensitivity to light may make them even more susceptible to dysregulation of sleep and the circadian system.” 

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