Almost one-third of children show growing signs of addiction to mobile phones, social media and video games starting at age 11, according to a landmark study on the impact of modern technologies on the adolescent mind.

These young users are more likely to suffer mental health problems than peers who exhibit less compulsive behaviour patterns, according to research published in the Journal of the American Medical Association (Jama) on Wednesday.

The US study is a rare effort to capture multiyear trends in online behaviours and to assess potential links with poor mental health. It suggests bad outcomes are not associated with high screen time in itself, but with cravings, difficulty in stopping and interference with sleep, school or relationships, researchers said.