People who log more hours in front of the television are at greater risk of dying, or developing diabetes and heart disease, a new study suggests.

"The message is simple," study author Dr. Frank Hu at the Harvard School of Public Health told Reuters Health. "Cutting back on TV watching is an important way to reduce sedentary behaviors and decrease risk of diabetes and heart disease."

Every day, Americans spend an average of 5 hours watching television while Australians and some Europeans log 3.5 to 4 hours a day, the researchers note.

People who sit in front of the TV are not only not exercising, they are likely eating unhealthy foods, Hu explained. "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 kids 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 previous research that had examined the link between TV time and diseases such as type 2 diabetes, the form of the disease closely associated with obesity.

In the end, their analysis included 8 studies that followed more than 200,000 people for an average of 7 to 10 years.

Hu and his team found that for every 2 hours of daily television people watched, their risk of diabetes increased by 20 percent, while their risk of heart disease rose by 15 percent. Each 2 hours of television per day increased the risk of dying by 13 percent.

Based on those results, the researchers estimated that, among a group of 100,000 people, reducing daily TV 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 included studies ensured that participants did not have a chronic disease—because people who were generally sicker might be more likely both to watch many hours of TV and to experience diabetes, heart disease, or premature death.

But, Hu and his colleagues caution, it remains possible that some people had undetected forms of disease at the outset of the studies, which could influence the findings.

The study cannot prove that TV watching, per se, causes the increased risk for disease. Nor can it identify what, exactly, about TV watching might influence disease risk.

"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 noted. People who watch a lot of TV are more likely to eat junk foods, he explained, but unhealthy diet and inactivity are also consequences of prolonged TV watching, so they explain some of the adverse effects of the sedentary behavior.

"'Couch potatoes' are more likely to get type 2 diabetes and heart disease, and more likely to die of chronic diseases," said Hu.

"I'm sure we've all unintentionally lost evenings slumped on the sofa in front of the TV snacking on crisps and biscuits and drinking sugary drinks or alcohol," said Maureen Talbot, a senior cardiac nurse with the British Heart Foundation who was not involved in the study. "But it's important that this doesn't become a regular activity."

"We should try to be selective in how much time we spend watching the TV, and try to be more physically active instead," said Talbot in a statement responding to the new findings. "We need 30 minutes of physical activity at least five days a week to keep our hearts healthy, so why not take a walk after work, join a sports team or even just get out for a bit of gardening in the evenings. It's bound to be a lot more rewarding than staring at the box."