In a provocative look at the impact of sedentary behavior. on health, a new study links ti

me watching television to an increased risk of death. One of the most surprising findings is that it isn't just couch potatoes who were affected—even for people who exercised regularly, the risk of death went up the longer they were in front of the TV. The problem was the prolonged periods of time spent sitting still.

Australian researchers who tracked 8,800 people for an average of six years found that those who said they watched TV for more than four hours a day were 46% more likely to die of any cause and 80% more likely to die of cardiovascular disease than people who reported spending less than two hours a day in front of the tube.

Time spent in front of TVs and computers and videogames has come under fire in studies in recent years for contributing to an epidemic of obesity in the U. S. and around the world. But typically the resulting public-health message urges children and adults to put down the Xbox controller and remote and get on a treadmill or a soccer field. The Australian study offers a different take. "It's not the sweaty type of exercise we're losing," says David Dunstan, a researcher at Baker IDI Heart and Diabetes Institute, Melbourne, who led the study. "It's the incidental moving around, walking around, standing up and utilizing muscles that doesn't happen when we're plunked on a couch in front of a television." Indeed, participants in the study reported getting between 30 and 45 minutes of exercise a day, on average.

The results are supported by an emerging field of research that shows how prolonged periods of inactivity can affect the body's processing of fats and other substances that contribute to heart risk. And they suggest that people can help mitigate such risk simply by avoiding extended periods of sitting. The report, being published Tuesday in the American Heart Association journal Circulation, focuses on TV watching in part because it is the predominant leisure-time activity in many countries, researchers said, especially in the U. S. A study by ratings firm Nielsen Co. found that Americans averaged 151 hours of TV viewing a month in the fourth quarter of 2008—more than five hours a day. Dr. Hamilton says studies suggest that after just one day of inactivity, levels of HDL, or good cholesterol, which helps transport LDL or bad cholesterol out of the blood stream, can fall by as much as 20%.

Keeping such processes working more effectively doesn't require constant intense exercise, but consciously adding more routine movement to your life might help, doctors say. "Just standing is better than sitting," says Gerard Fletcher, a cardiologist at Mayo Clinic, Jacksonville, Fla., who works standing up at his computer. "When you stand up, you shuffle around a little bit and use muscles not required when you're sitting or lying down". Simple strategies for increasing activity include incorporating household chores such as folding laundry into TV-watching time or getting up to change a TV channel rather than using a remote control.

According to the study, even for people who exercised regularly, the risk of death went up the longer they were in front of the TV. What's the reason？