The amount of time children spend using screens, such as televisions and computers, on a daily basis exceeds recommended guidelines but those guidelines were drawn up at a time when tablets, cell phones and other mobile devices were not as present in everyday life. Unless you are Amish or a doomsday prepper, it is unlikely that the future will mean current screen time guidelines.

And how valid are they anyway? Yes, prolonged use of screens by children is associated with adverse physical and mental health outcomes, such as increased risk of depression and anxiety in adolescent girls, but that is epidemiological curve fitting based on surveys, not real data.

A longitudinal study could start to provide real data though. In 2001 the American Academy of Pediatrics published recommendations that children under the age of two should have no exposure to screens and those over the age of two should have their exposure limited to less than two hours a day. These guidelines and most follow-up studies have been based on asking children about watching TV and playing computer games and without asking about other types of screen media.

To address this, researchers from the University of Western Australia surveyed 2,620 children aged eight to 16 years from 25 primary and secondary schools in Australia. The schoolchildren were shown different screen types, these included: iPad, iPod Touch, laptop, Portable PlayStation, laptop computer and Xbox, and given examples of the different types of activities that could be done with these screens: watch TV, use instant messenger, play computer games, do school and homework.

They were then asked about how many hours they used these screens, from when they woke up until they went to bed, including before, during and after school. It was found that an average of 63% of respondents exceeded the recommended guidelines of less than 2 hours. The most popular screen use with all participants was TV, with 90% of reporting watching TV in the last week; this was followed by laptop (59%), iPad/tablet (58%) and mobile phone (57%).

There was variation on screen use within individual age groups: 45% of the youngest participants (aged eight years) exceeded the guidelines, and 80% of those aged 14-15 years. There was also a difference in screen use between the sexes as noted by lead researcher Stephen Houghton: "As anticipated boys were more likely than girls to exceed the less than 2 hours recommendation for playing computer games. But it was unexpected that girls were more likely than boys to exceed the less than 2 hours recommendation for social networking, web use, and TV/DVD/movies."

"Of particular interest is the rate at which girls are more likely to exceed the less than two hours recommendation for social networking as they got older. Specifically, by 15 years of age girls were over 15 times more likely to exceed the less than 2 hours recommendation compared to their Grade 3 (8 year old) peers, and almost 7 times more so than boys."

This study was based on self-reported use of using different types of screens but did not investigate how this has a direct effect on the children's health. Future studies should try to address this by having more objective measurements on screen use and what impact it has on health.

Stephen Houghton says: "The introduction of mobile devices suggests the less than two hours per day recommendation may no longer be tenable given the surge in social media engagement and school derived screen use. Guidelines for appropriate screen use, should also take into account the extent to which screen use differs across form, activity, sex, and age."

CitatioL Virtually Impossible: Limiting Australian children and adolescents daily screen based media use
Stephen Houghton, Simon C Hunter, Michael Rosenberg, Lisa Wood, Corinne Zadow, Karen Martin and Trevor Shilton
BMC Public Health 2015, 15:5