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Screen time before bedtime could be especially damaging to preteens

Experts have been warning for the last few years that mobile device and computer screens diminish sleep quality, but a new study suggests the effect could be particularly detrimental for children and young teenagers.
Nighttime light exposure of any kind can imperil sleep, yet the new study says that pubescent boys and girls between the ages of nine and 15 are particularly sensitive – more so than older teens.
"Students who have tablets or TVs or computers – even an 'old-school' flashlight under the covers to read – are pushing their circadian clocks to a later timing," says senior author Mary Carskadon of Brown University in the US. "This makes it harder to go to sleep and wake up at times early the next morning for school."
In the study, just one hour of nighttime exposure to light suppressed production of sleep-inducing hormone melatonin for a participant group of 38 boys and girls between the ages of nine and 14 years who were in the earlier stages of puberty.
On the flipside, the suppression of melatonin was less dramatic for a group of 29 boys and girls between the ages of 11.5 and 15.9 years old who had progressed farther into puberty.
Melatonin samples were collected every 30 minutes using participants' saliva, and light exposure started at 15 lux, the rough equivalent to twilight, which suppressed melatonin by 9.2 percent in the younger group.
Lighting was then brightened to 150 lux (the approximate level of a residential home) and the younger group's melatonin production dwindled by 26 percent and 500 lux (as bright as in an office) diminished melatonin production by 36.9 percent.
For the older group, 15 lux made no difference in melatonin production, while exposure to 150 lux diminished production by 12.5 percent and 500 lux caused it to drop by 23.9 percent.
The researchers noted no differences between boys' and girls' responses to the light exposure.
"Small amounts of light at night, such as light from screens, can be enough to affect sleep patterns," says Carskadon, who is the director of chronobiology and sleep research at the EP Bradley Hospital in East Providence, Rhode Island in the US.
Carskadon and her co-authors recommend limiting screen time before bedtime, acknowledging that this could be difficult, for studies suggest a large proportion of teens turn on their gadgets in the hour before they go to sleep.
The study was published in the Journal of Clinical Endocrinology & Metabolism. 

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