Watching TV Linked to Higher Risk of Death

By RON WINSLOW

If you're reading this sitting down, you might consider standing up.

In a provocative look at the impact of sedentary behavior on health, a new study links time 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 televisions and computers and playing 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.

"If you're not up on your feet moving around, you're sedentary," says Marc Hamilton, a scientist at Pennnington Biomedical Research Center, Baton Rouge, La., who studies the biology of inactivity and who wasn't involved with the Australian study.

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.

But Dr. Dunstan says the results also likely apply to such sedentary activities as sitting in front of a computer, reading a book, driving or taking the train to work. Indeed, a recent Canadian study, for instance, linked increasing time spent sitting down for any reason to higher risk of death from heart-related reasons and from any cause.

None of this diminishes the importance of the benefits derived from breaking a sweat and getting your heart rate up during regular vigorous physical activity, he says. But even if you get eight hours of sleep and spend 30 to 60 minutes a day working out, that leaves at least 15 hours for other activities. "The implication of these findings is that the extraordinary amount of sitting can undo the good effects that we know are a benefit when we get regular exercise," Dr. Dunstan says.

Participants in the study were 50 years old on average when they enrolled in 1999 and 2000. After an average six years of follow-up, 284 of the participants died, including 87 from cardiovascular causes and 125 from cancer.

A limitation of the study is that information on TV watching time and exercise was obtained at enrollment and not otherwise verified or checked during the remainder of the study, but researchers said the findings are consistent with other research.

Dr. Dunstan says other research shows the important role of muscle movement in how the body processes blood sugar and blood fats. "The absence of movement can slow down our metabolic processes," he says. "When we're sitting down or even lying on the couch, we're burning the equivalent of the energy we burn when we're sleeping."

Researchers reported that the risk of death from any cause increased by 11% for each hour a day of reported TV watching; for death from cardiovascular disease, the risk increased 18%. A heightened risk for death from cancer wasn't statistically significant, but the other findings held up even after adjusting not only for exercise, but for such risk factors as age, gender and waist circumference.

Dr. Hamilton of the Pennington research center cautions that such population-based studies can only show correlations, but his own study of what happens when people and animals become inactive offers support for the connections. For instance, after just a few hours of inactivity, an enzyme called lipoprotein lipase that pulls fat from the blood shuts down, Dr. Hamilton says. Instead of fat being transported to muscle tissue where it is burned as fuel, fat accumulates in the blood stream, where over time it can damage arteries and lead to cardiovascular disease.

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.

Write to Ron Winslow at ron.winslow@wsj.com