Allowing children to have a television in their bedroom almost triples the risk of obesity and type 2 diabetes, a conference on sedentary behaviour in Sydney will hear this week.
New US research that studied 380 children aged from five to 18 found two-thirds had a TV in their bedroom, despite recommendations against it by the American Academy of Pediatrics.
A TV in the bedroom - and watching it for more than two hours a day - were associated with greater odds of increased waist circumference and elevated [artery blocking] triglyceride levels, despite exercise and limited sugary drinks.
The study, headed by Amanda Staiano, from the Pennington Biomedical Research Centre, to be published in January, concluded: ''Parental education to reduce television could protect youth against the development of obesity and an adverse cardiometabolic profile.''
Dr Staiano will speak at the Be Active 2012 conference, at which more than 1000 research papers relating to sedentary behaviour and getting kids active will be presented.
If they end up sitting for prolonged periods then they are going to die earlier.
In an interview from the US, Dr Staiano said parents should monitor TV time and aim for less than two hours a day as ''reduced television viewing could protect our youth''.
Curtin University professor of physiotherapy, Leon Straker, will tell the conference that schools have the opportunity to reduce sedentariness but that his study found children were actually more sedentary at school. Protracted periods of sitting for more than half an hour without a break was detrimental to health, he said.
The body goes into a type of ''hibernation'', like a computer in low power mode, which should be prevented by frequent breaks to move around. ''Schools are teaching skills for life and [students] should be taught to never sit down for more than half an hour,'' he said.
''If they end up sitting for prolonged periods then they are going to die earlier. The body is not designed to sit still for long periods, it is designed to be mobile.''
Professor Straker said TVs, computers and electronic games should be in common family rooms, not bedrooms, for a variety of social and physical reasons.
British research will show that children have 4.5 hours of sedentary time each day between the ages of three and six. This figure increases as they get older and, by age 10, they have six hours of sedentary time and nearly eight by the age of 17 to 18.
Primary school teacher Alison Rasheed, from Castle Crag, has two boys, Henry, 9, and Fraser, 4. She allows TV and computer time as a reward after homework and activity.
''Sometimes it is an effort to get them to go outside but it is much easier now it is light in the evening,'' Ms Rasheed said.