A study of more than 53,000 Korean adolescents has reported that even moderate smartphone use may influence teens' diet and weight. Researchers from Korea University found that adolescents who used a smartphone for more than two hours per day were significantly more likely to eat more junk food and fewer fruits and vegetables than those spending less time on their phone. – and those who spent more than three hours per day on a smartphone were significantly more likely to have overweight or obesity.
"While earlier studies have shown that TV watching is an important factor that increases the risk of obesity in children and adolescents, little is known about the effects of modern screen time such as smartphone use on diet and obesity," said Dr Hannah Oh, assistant professor at Korea University and the study's senior author. "Our data suggest that both smartphone usage time and content type may independently influence diet and obesity in adolescents."
The researchers analysed data from the Korea Youth Risk Behavior Web-Based Survey, a nationally representative sample of over 53,000 Korean adolescents 12-18 years old. After accounting for variables such as socioeconomic status that may influence both obesity and smartphone ownership, the researchers examined the prevalence at which participants engaged in healthy behaviours (eating fruits and vegetables) and unhealthy behaviours (skipping breakfast and consuming fast food, chips, instant noodles or carbonated or sweetened beverages) relative to the amount of daily smartphone use and the types of content used.
Adolescents spending five or more hours per day on their phone were more likely to report consuming carbonated and noncarbonated sugar-sweetened beverages, fast food, chips, and instant noodles, compared to those spending less than two hours per day on their phone (Figure 1).
Those who reported using their phones more for information search and retrieval overall had healthier eating behaviours than those using their phones more for chatting/messenger, gaming, video/music and social networks. Respondents who used their smartphone most frequently for gaming, video/music or webtoon/web-novel were more likely to be overweight or obese.
Oh explained potential drivers behind these trends could include exposure to food marketing in digital spaces, an increased propensity toward "mindless" eating while using a smartphone, inadequate sleep, or the displacement of time that would otherwise be spent on physical activity. She stressed the need to monitor food marketing targeting adolescents in digital media and, if warranted, work to prevent teens from being exposed to aggressive marketing or misleading messages about unhealthy foods.
On the flip side, she noted that smartphones could be leveraged to improve public health through nutrition-tracking apps or by using digital platforms to make information about healthy eating more accessible.
"Adolescents of today are digital natives, who have grown up in close contact with digital devices such as smartphones, and thus are likely to be heavily influenced by them," said Oh and Ryu. "Efforts should be taken to maximize the positive effects and minimize the negative effects of smartphone use on adolescent health."
The researchers cautioned that the study was not designed to determine the temporal relationship between obesity and smartphone use; a longitudinal, prospective study would be needed to assess changes in body weight and smartphone use over time.