It is already well established that children who watch too much television have an increased risk of becoming obese. However, a new study has found similar concerns when it comes to other screens, such as smartphones and tablets.

According to US researchers, there have been many studies that have assessed the impact of TV on childhood obesity, however far fewer studies have assessed the impact of other screen devices. They decided to look into this further.

They looked at the screen viewing habits of almost 25,000 teenagers aged 14-17. The data included details on how many hours per day they spent on various screens, how much sleep they got on an average school night and how much exercise they undertook.

The study found that almost 20% of the teenagers spent more than five hours per day using devices such as smartphones, tablets and computers, compared to 8% who watched more than five hours per day of television.

While watching a lot of TV continued to be associated with an increased risk of obesity and poor diet among the teenagers, the researchers also found unhealthy habits among those using other screens.

For example, those who spent at least five hours per day on other devices were twice as likely to consume a sugary drink every day, not get enough sleep at night and not exercise enough.

Overall, these teens were 43% more likely to be obese compared with teenagers who did not spend 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," the researchers from Harvard said.

They added that until more research is done, families should be encouraged to set time limits for both television and other screen devices.

Details of these findings are published in The Journal of Pediatrics.