These youngsters are exhibiting "problematic smartphone usage", meaning they use the devices in way that is consistent with a behavioural addiction, scientists found.

The study, by researchers at King's College London and published in BMC Psychiatry, analysed 41 studies published since 2011 on smartphone usage and mental health.

It concludes that between 10 per cent and 30 per cent of children and young people use their phones in a dysfunctional way, meaning that on average 23 per cent were showing "problematic smartphone usage" (PSU).

The KCL researchers defined PSU as behaviour linked to smartphone use that has an element of addiction - such as anxiety when the phone is unavailable or causing neglect of other activities.

The study also concludes that there are links between PSU and mental health issues such as anxiety, stress, poor sleep and depressed moods.

Co-senior author Dr Nicola Kalk from the Institute of Psychiatry, Psychology and Neuroscience, said: "Smartphones are here to stay and there is a need to understand the prevalence of problematic smartphone usage.

"We don't know whether it is the smartphone itself that can be addictive or the apps that people use.

"Nevertheless, there is a need for public awareness around smartphone use in children and young people, and parents should be aware of how much time their children spend on their phones."

The study authors note that 22 of the studies examined were of "poor methodological quality" and there was wide variation across the research analysed in the definitions of PSU.

"One challenge for the field, in light of this valuable meta-analysis, is that problematic smartphone use is not consistently defined," Dr Sam Chamberlain, Wellcome Trust Clinical Fellow, Honorary Consultant Psychiatrist, University of Cambridge, said.

"As noted by the authors, research into an accepted and validated set of criteria is urgently needed."

Australian Associated Press