NEW YORK - People who spend more hours in front of the television are at greater risk of dying, or developing diabetes and heart disease, with even two hours of television a day having a marked effect, according to a US study.
Every day, US residents spend an average of 5 hours watching television, while Australians and some Europeans log 3.5 to 4 hours a day, said researchers led by Frank Hu, at the Harvard School of Public Health.
"The message is simple. Cutting back on TV watching is an important way to reduce sedentary behaviors and decrease risk of diabetes and heart disease," Hu said.
People who sit in front of the television are not only exercising less, they are likely eating unhealthy foods, he added.
"The combination of a sedentary lifestyle, unhealthy diet and obesity creates a 'perfect breeding ground' for type 2 diabetes and heart disease."
This is not the first study to associate TV time with ill effects. Many studies have found a strong link to obesity, and one 2007 report found that more TV time was associated with higher blood pressure in obese children.
Another study that same year found that overweight children who watch food advertisements tend to double their food intake.
For the new study, published in the Journal of the American Medical Association, Hu and his team reviewed 8 studies examining the link between television time and diseases, that in total followed more than 200,000 people, for an average of 7 to 10 years.
Hu and his colleagues found that for every two hours of daily television that people watched, their risk of diabetes increased by 20%, while their risk of heart disease rose by 15%.
Each two hours of television per day increased the risk of dying by 13%.
Based on those results, Hu and his team estimated that, among a group of 100,000 people, reducing daily television time by 2 hours could prevent 176 new cases of diabetes, 38 cases of fatal cardiovascular disease, and 104 premature deaths -- every year.
All of the studies in the analysis made sure that participants didn't have a chronic disease, because people who were generally less well might be more likely both to watch many hours of TV and to experience diabetes, heart disease or premature death.
But Hu and his team cautioned that it's possible some people had undetected forms of disease at the start of the studies, influencing the findings.
The study cannot prove that TV watching alone raises the disease risk, nor can it identify what about TV watching might have an impact.
"It's true that people who watch a lot of TV differ from those who watch less, especially in terms of diet and physical activity levels," Hu said.
He added that people who watch a lot of television are more likely to eat junk food. But unhealthy diet and inactivity are also consequences of prolonged television watching, so they explain some of the adverse effects of the sedentary behavior.