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Sept. 6, 2007 -- Tiptoe past a teen's room after bedtime, and you might see a cell phone's glow underneath the doorway.
Many teens talk or text message on their mobile phones after bedtime at least occasionally -- and the more often they do it, the more tired they are.
That news appears in the latest edition of the journal Sleep.
Data came from more than 1,600 teens at 15 schools in Flanders, Belgium. They rated their tiredness and reported how often they send or receive calls or text messages on their mobile phones after bedtime.
"A lot of sending and receiving text messages and telephone calls appeared to go on in the bedroom," writes Jan Van den Bulck, PhD, DSc, of Belgium's Katholieke Universiteit Leuven.
In fact, only 38% of the teens reported never using their cell phones after bedtime.
Teens were more tired if they used their cell phones after bedtime, the study shows.
Those teens who were very tired were particularly likely to report frequently using their cell phones after bedtime.
"The risk of being very tired more than doubled in those who used their mobile phone less than once a week, it tripled in those who used them weekly, and was more than five times higher in those who used it several times a week or more," writes Van den Bulck.
Teens typically used their cell phones right after bedtime. But some kept chatting or texting past 3:00 a.m., the study shows.
Van den Bulck warns that "as mobile phones become ever more complex (integrating radio, television, and MP3 technologies) the attraction to use them after lights out is likely to increase further."