Mobile phones are keeping children awake at night, new research has revealed.

A study to be published in the September issue of the journal Sleep suggests that mobile phone use after bedtime is "very prevalent" among adolescents, and is related to increased levels of tiredness.

The research by Jan van den Bulck, of the Leuven School for Mass Communication Research in Belgium, focused on 1,656 school children with an average age of 13.7 years in the youngest group and 16.9 years in the oldest group.

Only 38 per cent of the subjects never used their mobile phones after bedtime, according to the results, and those using mobiles less than once a month increased the odds of being very tired one year later by 1.8.

Those who used it less than once a week were 2.2 times more likely to be very tired. Using mobiles about once a week increased the odds by 3.3, and those who used them more than once a week were 5.1 times more likely to be very tired.

Overall, 35 per cent of the cases of being very tired were attributed to the use of mobile phones.

Use of the phone right after bedtime increased the odds of being very tired by 2.2. Between midnight and 3am, the odds were 3.9 times higher, and in those who used it at any time of the night, the odds were 3.3 times higher.

"Parents often worry about the hazards of media use when they think about the time children spend watching TV or listening to music or surfing the internet," said Dr van den Bulck.

"The mobile phone, on the other hand, is usually seen only as a simple communication device, useful in emergency situations.

"This study shows that parents should be aware of the fact that young people today use the modern means of communication in ways they probably cannot imagine.

"Communication and staying in touch are important for young people, and they now have the technology to stay 'connected' more or less permanently.

"Taking a mobile phone to your bedroom is not trivial. They spend a lot of time 'connecting' to other people, and some of them do this all hours of the night."