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Letting kids use phones for short time before bed still hurts their sleep

The new study found high levels of melatonin suppression following exposure to all types of light, including dim ones.

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Small girl staring at cellphone screen at night. Cute kid lying on floor watching cellphone screen
(True Touch Lifestyle via Shutterstock)

By Gwyn Wright via SWNS

Letting young children use phones or other gadgets for just a short time before bed still damages their sleep, warns a new study.

Scientists say levels of the critical sleep-promoting hormone melatonin plummet in three to five-year-olds who have been exposed to a small amount of light in the hour before bedtime.

Half of children stare at screens before bed but the researchers say parents should turn off their kids gadgets at least an hour before lights out.

If they do not their little ones’ slumber may be disrupted for hours when they are supposed to be fast asleep.

American researchers found light suppressed melatonin levels by between 70 and 99 percent.

Surprisingly, the team found little-to-no relationship between how bright the light was and how much the key sleep hormone fell.

In adults, this intensity-dependent response has been well documented.

Melatonin fell by as much as 78 percent even when the young ones were exposed to dim light.

After 50 minutes, melatonin levels had not rebounded in more than half of children.

Earlier research has shown looking at one fairly intense bright light before bedtime dampens melatonin levels by 90 percent.

The new study found high levels of melatonin suppression following exposure to all types of light, including dim ones.

Light is the body’s main time cue and influences circadian rhythms which regulate everything from when we feel tired or hungry to our body temperature throughout the day.

When it hits our eyes, it transmits a signal to a part of the brain called the suprachiasmatic nucleus, which coordinates rhythms throughout the body, including nightly production of melatonin.

If exposure happens in the evening as melatonin is naturally increasing it can slow or halt it, delaying the body’s ability to transition into biological night-time.

Because children’s eyes have bigger pupils and more transparent lenses than adults, light streams into them more freely.

For the new study, the team recruited 36 healthy three to five year olds who wore a wrist monitor that tracked their sleep and light exposure.

For seven days, parents kept their kids on a stable sleep schedule to normalize their body clocks and settle them into a pattern in which their melatonin levels rose at about the same time each evening.

On the eighth day, researchers transformed the children’s home into a “cave” with black plastic on the windows and lights dimmed.

They then took saliva samples every half hour from the early afternoon until bedtime.

This helped the researchers understand when the children’s biological night naturally began and what their melatonin levels were.

On the last day of the study, the tots were asked to were asked to play games on a light table in the hour before bedtime.

This is a posture similar to a person looking at a glowing phone or tablet.

Different children were shown different amounts of light.

"Kids are not just little adults," said study senior author Professor Monique LeBourgeois, of the University of Colorado Boulder.

“This heightened sensitivity to light may make them even more susceptible to disregulation of sleep and the circadian system.

“This does not necessarily mean that parents must throw away the nightlight and keep children in absolute darkness before bedtime.

“But at a time when half of children use screen media before bed, the research serves as a reminder to all parents to shut off the gadgets and keep light to a minimum to foster good sleep habits in their kids.”

She added: "Some children are more sensitive to light than other children, which means it’s even more important for parents to pay attention to their child’s evening light exposure.”

The findings were published in the Journal of Pineal Research.

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