Seoul, Dec 7 : Adolescents who indulge in smartphones for more than four hours daily could be at higher risk of adverse mental health and substance use risk, according to a study. Prior research has shown that smartphone use among adolescents has increased in recent years, and that this usage may be associated with higher risk of adverse health -- such as psychiatric disorders, sleep issues, eye-related problems, and musculoskeletal disorders. To deepen understanding of the relationship between adolescents' use of smartphones and health, the team from Hanyang University Medical Center, Korea analysed data on more than 50,000 adolescent participants. The data included the approximate number of daily hours each participant spent on a smartphone as well as various health measures. The statistical analysis employed propensity score matching to help account for other factors that could be linked to health outcomes, such as age, sex, and socioeconomic status. Adolescents who used a smartphone for more than four hours per day had higher rates of stress, thoughts of suicide, and substance use than those with usage below four hours per day. However, adolescents who used a smartphone one to two hours per day encountered fewer problems than adolescents who did not use a smartphone at all, revealed the findings published in the open-access journal PLOS ONE. The authors note that this study does not confirm a causal relationship between smartphone use and adverse health outcomes. Nonetheless, the findings could help inform usage guidelines for adolescents -- especially if daily usage continues to rise. "This research shows the impact of using smart devices for more than four hours a day on adolescent health," said Jin-Hwa Moon and Jong Ho Cha of Hanyang. 'The adverse effects of smartphone overuse became prominent after 4 hours of daily usage time. These results can help establish smart device usage guidelines and education programmes for appropriate media use,' they added. /IANS