Many parents already have concerns, but some may now have a new argument for limiting their children's "screen time" — addiction to video games has been recognized by World Health Organization as a mental health disorder.

The WHO's International Classification of Diseases (ICD), a reference bible of recognized and diagnosable diseases, describes addiction to digital and video gaming as "a pattern of persistent or recurrent gaming behavior" that becomes so extensive it "takes precedence over other life interests.

The WHO's expert on mental health and substance abuse, Shekhar Saxena, said some of the worst cases seen in global research were of gamers playing for up to 20 hours a day, forgoing sleep, meals, work or school and other daily activities.