Kids who watch TV in their bedrooms are twice as likely to be overweight and have almost three times the risk of heart disease and diabetes as those who don't, according to US research.
Scientists from Pennington Biomedical Research Center in LA studied children aged five to 18 and found the ones with TVs in their rooms were up to 2.5 times more likely to have a higher fat mass and larger waist.
Those who watched TV for more than five hours a day had double the risk of fat surrounding their internal organs, which can cause disease.
"It's really troubling to see these kids with fat around their heart and liver," said study author Dr Amanda Staiano.
Previous studies have found a link between being overweight and more TV viewing, so this study sought to establish where the kids were adding fat and how their risk of heart disease and diabetes was affected.
They looked at 369 children and teens, measuring their height, weight, waist, blood pressure and fat deposits.
"We wanted to see a more precise relationship between TV and health," said Stainao.
Sixty-six percent of the participants had bedroom TVs and a third watched five or more hours of TV a day.
The study could not determine whether it was the TV in the bedroom or the long hours that caused the health problems, but the study has renewed calls for TVs to be banned in children's rooms.
Australian studies have found almost half of secondary school children have TVs in their bedrooms and a quarter of children aged five to 17 years old are obese.
Professor Boyd Swinburn, an obesity expert from Deakin University, told ninemsn that TV viewing has consistently been linked with childhood obesity.
"Kids who have TVs in their bedrooms are more likely to watch more TV," he said.
"The interesting thing is that TV viewing seems to work through both reducing physical activity and increasing food intake."
Professor Swinburn said parents ought to think twice before putting a TV in their child's bedroom.
"Parents need to be aware that putting a TV in a child's bedroom is setting them up for a higher risk of watching more TV and thus unhealthy weight gain."
The study was published in the American Journal of Preventive Medicine.