Too much television time has long been linked to childhood obesity, but a U.S. study suggests that the connection holds true for smaller screens too, such as computers, gaming consoles, tablets and smartphones.
With TV, a minimum five-hour-a-day habit increased the odds of obesity by 78 percent compared with teens who didn't have TV time, the study found. Such heavy use of other screens was tied to a 43 percent greater risk of obesity, researchers report in the Journal of Pediatrics.
"The landscape has changed so quickly with regards to how much we all use mobile screen devices and computers," said lead study author Dr. Erica Kenney, a public health researcher at Harvard University in Boston.
"We have known for years now that spending too much time watching television contributes to a higher risk of developing obesity among kids, mostly because watching too much TV can lead to an unhealthy diet," Kenney added by email. "We see similar associations between other screen device use and diet, physical activity, and obesity risk as we've seen in the past for TV."
To assess how screens large and small influence the risk of obesity, researchers looked at nationally representative survey data collected in 2013 and 2015 on 24,800 adolescents in grades 9 to 12.
Nearly 17 percent of youth said they watched no TV on weekdays, while 7.8 percent said they watched five hours or more daily.
Nearly one in five teens in the study spent at least five hours a day using smaller screens during the week.
The survey also asked how many sugary drinks teens consumed and inquired about teens' height and weight.
More than 25 percent of boys and about 20 percent of girls reported consuming at least one soda or other sugar-sweetened beverage a day.
Approximately two-thirds of boys and three-quarters of girls said they didn't get daily exercise.
Overall, 14 percent of the teens in the study were obese.
After adjusting for age, sex, race and ethnicity and other time with tiny screens, TV viewing was associated with significantly higher odds of consuming one or more sugary drinks and an increased risk of obesity.
More time with other screens was independently linked to higher odds of insufficient sleep, drinking more sugary beverages and inactivity.
The study can't prove that television or time on smaller screens causes obesity, however.
It's also possible that excessive screen time was caused by obesity, inactivity or fatigue rather than these things being caused by too much time with TVs, smartphones or tablets, the authors note.
Some previous research has found TV causes obesity and that kids who cut back on television can improve their weight, said Dr. David Hill, a researcher at the University of North Carolina School of Medicine and chair of the American Academy of Pediatrics Council on Communications and Media.
The role of other screens has been less clear, with at least one study suggesting only passive TV watching affects obesity risk, Hill, who wasn't involved in the current study, said by email.
"This study helps us understand that the link between obesity and media use may extend to other types of screens," Hill said.
This connection may be at least in part due to ads teens see for unhealthy foods, Hill added. Decreased sleep is also tied to obesity, and too much screen time is known to interfere with the amount and quality of sleep teens get.
"We encourage parents to work with kids to examine what they need to accomplish in a day to be successful: how much sleep should they get, when should they eat, how much time do they need for homework, exercise, and family activities," Hill said. "Screen media time should then fit in around those activities or complement them rather than displacing them."