We know that physical activity is good for health.

But is the reverse also true: Is sitting — being sedentary — bad for health?

A study published last week in the online version of Circulation, the medical journal of the American Heart Association, suggests that it is. A team of Australian researchers reported that every hour a person spends watching TV each day is associated with an 18 percent increased risk of dying from cardiovascular disease and an 11 percent increased risk of dying prematurely from all diseases.

The more time spent glued to the TV, the greater the risk. Among the 8,800 adults who participated in the 6½-years-long study, those who watched the most TV — four or more hours a day — were 80 percent more likely to die of cardiovascular disease and 46 percent more likely to die of any cause than their peers who watched two hours or less.

But here’s the finding that should really get you up and out of your chair: The study discovered that the association between TV watching and death from cardiovascular disease was not only independent of such risk factors as smoking, blood pressure, cholesterol, weight and diet, but also of exercise.

In other words, being a couch potato may wipe out some or all of the benefits you get from your daily workout.

And Americans are notorious couch potatoes. One of the things that struck me while reading the Circulation study was how low the average household TV viewing time is in Australia: about three hours. Here in the States, the average household TV viewing time is about eight hours.

In fact, the only thing we Americans spend more time doing each day than watching TV is sleeping.

Of course, this study has its limitations. People who watch a lot of TV may be unhealthier to begin with, and although the Australian researchers took steps to eliminate such confounding factors, it’s possible that undiagnosed illnesses could have been responsible for some participants’ long hours in front of the TV. Furthermore, the participants self-reported how much time they spend watching TV. Such self-reports can be unreliable. (Who likes to admit, even to themselves, how much TV they watch?)

A new paradigm?
A lot more is known about the physiological reasons exercise helps people stay healthy than about why sedentary behavior might cause people’s health to deteriorate. Research suggests, however, that sitting for long periods of time may harm health by increasing blood glucose and cholesterol levels as well as body fat.

This study isn’t the first to show that being sedentary can be harmful to health regardless of physical activity. Recent studies from Canada and Japan have reported similar findings.

Given all this new data, it’s time we start thinking about sedentary behavior in a new way, argue three Swedish exercise specialists in an editorial published online Tuesday in the British Journal of Sports Medicine. [Note: The editorial does not appear to be available to general readers yet.]

Using the term sedentary behavior as a synonym for not exercising is misleading, they write. We should instead think of it as muscular inactivity.

In other words, when it comes to assessing our healthful behavior, we not only have to think about how much exercise we’re getting, but we also need to consider how much sitting around we’re doing.

“In the future,” the Swedish experts write, “the focus in clinical practice and guidelines should not only be to promote and prescribe exercise, but also to encourage people to maintain their intermittent levels of non-exercise daily activities. Climbing stairs rather than using elevators and escalators, 5 minutes of break during sedentary work, or walking to the store rather than taking the car will be as important as exercise.”

Excuse me. I’m going to get up from my desk now for a five-minute break. …