Questions asked about devices and sleep, and the survey was completed at school by children aged 17-19 years.
Published in the BMJ Open, the study of almost 10,000 adolescents found an effect from lesser amounts of screen time, too - a total of more than 2 hours on the devices outside of school hours was associated with both a longer time to get to sleep and a shorter amount of sleep then gained through the night.
Citing evidence that "almost all American adolescents (97%)" are reported to "have at least one electronic media device in their bedroom," the study authors refer to a "parallel shift" towards "poorer sleep over the past decades among adolescents."
Very little survey research into screen time before bed had assessed the use of modern electronic devices, the authors claim, so they designed a questionnaire that would look across "a wide range of new electronic devices" - PC, cell phone, MP3 player, tablet, game console and TV.
The total screen time investigated by the questionnaire took account of all extracurricular hours, not just the hour before bed, asking the adolescents: "Outside of school hours, how much time do you usually spend on the following on weekdays?"
- TV games (PlayStation, Xbox, Wii, etc.)
- PC games
- Internet chatting
- Writing and reading emails
- Using the PC for other purposes.
The 17-19-year-olds (who are high school students under the Norwegian system) could choose to answer either no time, less than a half-hour, between a half-hour and 1 hour, 2-3 hours, 4 hours or more than 4 hours.
The study compared answers from those adolescents who took an hour or more to get to sleep, with answers from those who took under an hour, to draw the correlations with use of electronic devices. On average, the teenagers reported needing between 8 and 9 hours of sleep before feeling rested, but:
- They were three times more likely to have under 5 hours of sleep if they spent over 2 hours emailing or chatting online
- This reduced sleep was over 3.5 times more likely if they spent over 4 hours in front of any type of screen.
Calls for updated screen time advice
"The recommendations for healthy media use given to parents and adolescents need updating," say the researchers, "and age-specific guidelines regarding the quantity and timing of electronic media use should be developed."
The authors add:
"The current recommendation is not to have a TV in the bedroom. It seems, however, that there may be other electronic devices exerting the same negative influence on sleep, such as PCs and mobile phones. The results confirm recommendations for restricting media use in general."
The paper concludes with a suggestion that teenagers with problems sleeping could be reached through the very devices the authors believe are causing the reduced sleep:
"While technology use may be a source of sleep deficiency, it may also serve as a medium of intervention, as internet-based interventions have proven to be effective, and cost-efficient, modes of treating sleep problems."
Other researchers have been calling for the sort of work presented in this study. Current guidelines to limit kids' screen-based media use "may not be tenable" - that was the view of researchers publishing in BMC Public Health last month. Their paper adds:
"The increasing use of screen-based media use [SBMU] in regular [elementary] school and high school classrooms during the regular school day, and for homework purposes, and for social networking, need also to be taken into account if a more accurate estimate of SBMU and its consequences (positive and negative) are to be ascertained."
"Media and children" guidance from the American Academy of Pediatrics confines itself to recommendations over screen time for entertainment purposes, failing to take into account the wider use of devices that is now happening throughout the day. It recommends parents limit this play use to 1 or 2 hours a day.
Lead author of the Norwegian analysis - Mari Hysing of the regional centre for child and youth mental health and child welfare, in Bergen, Norway - has previously used the same large population study to investigate the relationship between sleep and school attendance, finding that most types of ill-effect on sleep (from bedtime to sleep duration and more) result in poorer attendance.
Publishing the analysis of school attendance last November - from the same 2012 "youth@hordaland study" - she and her colleagues also found that failure to attend was associated with large discrepancies between bedtimes at the weekend versus those during the week.