Spending hours on smartphones and tablet devices has frequently been linked to exacerbating mental wellbeing, but new research claims the damage might start in users as young as two. After just one hour of screen time, children and adolescents may have less curiosity, lower self-control and lower emotional stability, which can lead to an increased risk of anxiety and depression, claims a US study published in the journal Preventive Medicine Reports. The researchers found that those aged 14 to 17 are more at risk for such adverse effects, but noticed the correlations in younger children and toddlers, whose brains are still developing, as well. The study found that nursery school children who used screens frequently were twice as likely to lose their temper. It also claimed that nine per cent of those aged 11 to 13 who spent an hour a day on screens were not curious in learning new things, a figure which rose to 22.6 per cent for those whose screen time was seven hours a day or more. Authors Professor Jean Twenge, of San Diego State University, and Professor Keith Campbell, of the University of Georgia, said: "Half of mental health problems develop by adolescence. "Thus, there is an acute need to identify factors linked to mental health issues that are amenable to intervention in this population, as most antecedents are difficult or impossible to influence. "Compared to these more intractable antecedents of mental health, how children and adolescents spend their leisure time is more amenable to change."