The research believes the amount of screen time children devote to these devices adds to an already excessive amount television and computers already command.

While the study cannot conclude these devices cause obesity, they are a factor in a sedentary lifestyle that has been implicated in an increase in weight and a decline in health.

The study is also timely as Christmas is connected to shopping online or catching up with television programmes or movies, as well as indulging in foods high in fat, salt and sugar.

Assessing device use​

Researchers from the Harvard T.H. Chan School of Public Health in the US, used a sample of 24 ,800 high school students aged 15-18.

These students were asked to report on the number of hours spent on screen devices (including smartphones, tablets, computers, and videogames) and watching television.

In addition, they were asked to record the number of hours of sleep they achieved on an average school night; the number of sugar-sweetened beverages consumed in the previous seven days; and the frequency of physical activity for the past seven days.

Lead by Dr Erica Kenney and Dr Steven Gortmaker, the team found close to 20% of subjects devoted more than five hours a day on smartphones, tablets, computers and videogames.

This compares to 8% of children devoting more than five hours a day in front of the television.

Interestingly, the influence of the screen extended towards dietary and lifestyle choices as those who exceeded five hours of screen time a day were twice as likely to consume sugary drinks each day and exhibit a lack of adequate sleep or physical activity,

The team calculated the chances of these children becoming obese increased to 43% when compared with children who spent less time on these devices.

"This study would suggest that limiting children's and adolescents' engagement with other screen devices may be as important for health as limiting television time,”​ said Dr Kenney, research fellow at the Harvard T.H. Chan School of Public Health.

"Until more research is done, clinicians may want to encourage families to set limits for both television and other screen devices.”​

Online marketing to kids ​

Screen time, can include online activity as well as TV, DVDs, and electronic games. It has already been associated with increased intake of sugared drinks, fast food, salty snacks as well as decreased intake of fruits and vegetables among 9-16 year olds. ©iStock/Rasulovs

A lack of physical activity as a result of excessive screen time is not the only contributing factor to weight gain.

Exposure to marketing of unhealthy foods and beverages both on the television and online has been well-documented as food and beverage advertising is highly prevalent among social media and other websites directed toward children and youth.

The link between screen time and its association with a higher intake of sugar-sweetened beverages, fast food, sweets and salty snacks has also been well established.

Increased TV viewing has also been linked with shorter and poorer quality sleep, which is itself associated with excess energy intake and weight gain.

“Although this study cannot determine whether the observed associations between different forms of screen media use and health behaviours are causal, these results are still a cause for concern for clinicians, public health professionals, and families,”​ the study concluded.

“Given the large body of research demonstrating that TV viewing leads to poor diet, lower physical activity and obesity, it seems quite plausible that the relationships observed are largely driven by screen time, rather than the other way around.” ​

Source: The Journal of Pediatrics​

Published online ahead of print, DOI: 10.1016/j.jpeds.2016.11.015​​

“United States Adolescents' Television, Computer, Videogame, Smartphone, and Tablet Use: Associations with Sugary Drinks, Sleep, Physical Activity, and Obesity.”​

Authors: Erica Kenney et al.