It’s not that Jensen and Dunstan are hyperactive. Rather, both are exercise researchers looking into the link between sitting down and premature death. And what they have found is disturbing enough that they both make sure they spend most of the day on their feet.
Jensen explains that he and his colleagues at Mayo, in Rochester, Minn., were studying weight control when they discovered that some people “spontaneously start moving round and don’t gain weight” when they have overeaten. These people don’t dash to the gym; they just walk more, hop up from the couch to run errands or find other excuses to get onto their feet. “This really got us thinking about this urge to move,” Jensen says, “and how important that might be for maintaining good health.”
That led them to a field known as “inactivity research,” which suggests that inactivity, particularly sitting, can be very bad for your health. It might sound like a statement of the obvious, but the killer point is this: Inactivity is bad for you even if you exercise. Heading to the gym is not a license to spend the rest of the day on your backside.
In 2010, a team led by Alpa Patel of the American Cancer Society in Atlanta analyzed the data from a 14-year study of 123,000 middle-aged adults. When they compared mortality rates of those who spent six hours a day or more sitting and those who reported three or fewer hours — and when they took into account other factors such as diet — they found something surprising: Extra time on the couch was associated with a 34 percent higher mortality rate for women and 17 percent higher for men in the 14 years after they joined the study. It is not clear why there is such a big sex difference.
In another study, a team at the University of Queensland in Australia analyzed data on the television viewing habits of 8,800 Australians. They calculated that each hour of television correlated with 22 minutes off the average life expectancy of an adult older than 25. In other words, people who watch six hours of television a day face the prospect of dying, on average, about five years younger than those who don’t watch any.
Many other studies have reached similar conclusions. In a review of all the evidence, Dunstan’s team concluded that there was a “persuasive case” that excessive sitting “should now be considered an important stand-alone component of the physical activity and health equation.”
An independent health risk
The message is clear: Sitting still for hours at a time might be a health risk regardless of what you do with the rest of your day.
Just as you cannot compensate for smoking 20 cigarettes a day by a good run on the weekend, a bout of high-intensity exercise may not cancel out the effect of watching TV for hours on end. Patel’s study found that people who spent hours sitting had a higher mortality rate even if they worked out for 45 to 60 minutes a day. The researchers call these people “active couch potatoes.”