London, Feb 3 (IANS): The more your teenage son chats on Facebook during the sleep hours, more he or she is at an increased risk of sleep problems and depressive symptoms, finds a study.

Researchers from University of Basel in Switzerland analysed more than 300 students and found that that teenagers who own smartphones spend more time online - also during the night which may affect their sleep.

"Due to wireless internet connections and cheap flat rates, teenagers with smartphones spend more time online and communicate with their peers for less money - for example via WhatsApp - which has changed their digital media use pattern profoundly," they noticed.

The results showed that during weekdays, teenagers with smartphones spent more time on the internet than their peers with conventional mobile phones; on average two hours compared to one hour.

In addition, they wrote more text messages daily - on average 85 messages compared to seven messages.

A particularly noticeable difference was found for the time when the teenagers were in their beds at night.

Only 17 percent of smartphone owners switched their devices off or put them on silent during the night compared to 47 percent of the teenagers with conventional mobile phones.

Moreover, teenagers with smartphones indicated to watch videos, to be online, and to text with friends more often during the night than their counterparts with conventional mobile phones.

"Most importantly, teenagers who used digital media at night had an increased risk for poor sleep and depressive symptoms," the team said.

The researchers recommend that teenagers who suffer from sleep disorders or severe daytime tiredness to switch their digital media devices off at least one hour before bedtime.

The findings were published in the Journal of Youth and Adolescence.