This study, led by Dr. Mari Hysing at the regional Centre for Child and Youth Mental Health and Child Welfare in Bergen, Norway, found that electronic devices of all kinds have a serious effect on sleep quantity and quality. Smartphones, PCs, tablet computers, games consoles, televisions and MP3 music players all produced problems

The study looked at 10,000 16 – 19- year-olds in Norway. Almost all said that they used one or more electronic devices before bedtime. The study found that those who used a computer in the hour before bedtime were nearly three times as likely to get less than five hours’ sleep. Using a mobile phone before bed nearly doubled the risk of having a poor night’s sleep.

The study also found that that the longer a teenager spent in front of a screen during the day, the worse quality sleep they were likely to have. Spending more than four hours a day in front of a screen was linked to a 49 per cent greater risk of taking longer than usual to get to sleep. On average, the teenagers said that they needed eight to nine hours of sleep to feel rested. Those who spent more than two hours online were more than three times as likely to sleep for less than five hours. Those who spent more than four hours in front of a screen were three and a half times were more likely to sleep for less than five hours.

Regular poor sleep raises the risk of serious medical conditions such as obesity, heart disease and diabetes and can even shorten life expectancy.

The bluish light that screens emit can prevent sleep because it mimics daylight and suppresses production of melatonin, which triggers sleep. Circadian rhythms in general would then be affected.

http://www.reuters.com/article/2015/02/03/us-teen-sleep-screen-time-idUSKBN0L72F420150203: