The latest research into the use of mobile phones suggests that they can cause sleep problems in teenagers.
The researchers warn that excessive use of mobile phones makes teenagers more restless and can exacerbate sleep problems and stress.
The researchers from Sahigren's Academy, Gothenburg in Sweden carried out a study examining mobile phone use in teenagers age 14 to 20.
The group of 21 youngsters were divided into two groups according to their phone use - one group made fewer than five calls or sent fewer than five text messages a day, while the other made more than 15 calls and sent more than 15 messages.
There were three men and seven women in the low cell phone use group and three men and eight women in the high use group.
The teenagers wore wrist watches which monitored their activity level throughout the day and also kept sleep diaries and answered questionnaires to assess their level of stress and anxiety.
During the week-long study, the researchers conducted one at-home sleep study to measure how well the teenagers slept.
The scientists found that the teenagers who used their phones often were more restless and also had more 'careless' lifestyles.
They also consumed more stimulating drinks, suffered from disrupted sleep or insomnia and were more susceptible to stress and fatigue than young people who receive five or fewer calls or text messages each day.
Dr. Gaby Badre, the lead author of the study says addiction to phones is becoming common and youngsters feel under pressure to be interconnected and reachable 24 hours a day.
Dr. Badre says youngsters need to be informed of the negative effects of excessive phone use on their sleep-wake patterns, attention and cognitive problems and the associated serious health risks.
Dr. Bader says it is not the phone use per se or the electromagnetic field which causes the problems but rather the buildup of tension from being constantly connected which creates the stress and disturbed their sleep.
Dr. Bader suggests restricting phone use and instituting cell-phone-free slots during the day and he says adolescents need to have nine hours of sleep each night.
The research was presented at Sleep 2008, the annual meeting in the U.S. of the Associated Professional Sleep Societies.