LONDON (TIP): Excessive use of smartphones and computers throughout the day can worsen quality of sleep in teenagers, a study has found.

Researchers surveyed almost 10,000 teenagers aged 16-19 in Norway and concluded that recommendations on use of gadgets should be updated, and extended to tablets and smartphones.

Total screen-use time of over four hours was linked to a 49% higher chance of the teens taking longer than 60 minutes to fall asleep. A total of more than 2 hours of screen time after school was linked to both longer sleep onset latency and shorter sleep duration.

On an average, teenagers need 8-9 hours of sleep each day . But those who spent more than 2 hours emailing or chatting were more than 3 times as likely to sleep for less than 5 hours.

While those who spent more than 4 hours in front of any screen were more than 3.5 times as likely to sleep for less than 5 hours. Use of a computer, smartphone, or Mp3 player in the hour before bedtime was associated with taking longer to fall asleep. The effect was more pronounced in multitaskers. Teens who used 4 or more devices were 26% more likely to take 60 or more minutes to fall asleep than those who used one. Teens who used 2-3 devices were 50% more likely to sleep for less than 5 hours than those who used just one; those who used 4 or more devices were 75% more likely to do so. Screen use may simply replace sleep time or interfere with sleep by stimulating the nervous system, said the researchers.