TUESDAY, June 14 (HealthDay News) -- Couch potatoes beware: All those hours in front of the TV may be making you sick, or even killing you.

Watching television for two to three hours or more per day is linked to significantly higher risks of developing diabetes and heart disease and dying from all causes, according to a new analysis from the Harvard School of Public Health.

Noting that Americans watch an average of about five hours of TV per day -- the most common daily activity aside from working and sleeping -- researchers analyzed data from eight studies done between 1970 and 2011 on the association between TV viewing and incidence of type 2 diabetes, fatal or nonfatal cardiovascular disease and all-cause mortality.

Two hours of daily television watching was tied to a 20 percent greater risk for diabetes, a 15 percent higher chance of cardiovascular disease and a 13 percent elevated risk for all-cause deaths, according to the new Harvard meta-analysis, a type of research that pools data from different studies on an issue and analyzes them to look for statistical trends.

The findings are published June 15 in the Journal of the American Medical Association.

"The results really are not surprising at all. We already know that people who watch a lot of TV are more likely to eat an unhealthy diet and be obese," said senior study author Dr. Frank B. Hu, a professor of nutrition and epidemiology. "The message is actually quite simple . . . those who watch a lot of TV should cut back on TV watching and do more of something else."

Americans are hardly extraordinary in being glued to the tube. Hu pointed out that many people around the world structure their days in a similar fashion, with Europeans and Australians respectively spending an average of 40 percent and 50 percent of their daily free time watching television.

Prior research has established the negative health effects of TV viewing, including associations with less physical activity and unhealthy eating, such as higher consumption of fried foods, processed meat and sugar-sweetened beverages and lower intake of fruits and vegetables. Cancer incidence has not typically been studied in relation to TV watching, Hu said.

"There's no question this paper draws attention to the number of studies now that all seem to show the same thing," said Dr. Martin Abrahamson, chief medical officer of the Joslin Diabetes Center in Boston. "There are always limitations to these meta-analyses, but I think they're telling us a message we need to take heed of."

Based on disease incidence in the United States, Hu and his colleague, Anders Grontved, estimated that each two-hour increment of TV watching each day was linked to an absolute risk of 176 new cases of type 2 diabetes, 38 new cases of fatal cardiovascular disease and 104 new cases of all-cause mortality among 100,000 people per year.

Abrahamson and Hu agreed that the particularly ominous influence that TV has on diabetes incidence is due largely to its link to obesity, one of the biggest contributors to diabetes.

They also said that those who spend several hours per day exercising may be able to offset the negative health effects of prolonged TV watching, but that few tend to split their time equally between the two disparate activities.

"Certainly any physical activity would be beneficial regardless of the amount of TV you watch," Hu said. "But the reality is that people spend almost five hours a day watching TV. How much exercise do they do? There is a huge imbalance."

More information

The Nemours Foundation has more on the health effects of TV viewing among children.