Scientists are just beginning to investigate how sitting affects health, and early evidence has linked an excess of sitting time to all kinds of chronic maladies, particularly heart disease, diabetes and cancer. Now, a new analysis published in the British Medical Journal suggests that the life expectancy of the entire U.S. population could increase if Americans simply reduce the time they reduce channel-surfing on the sofa.
Researchers looked at the results of five studies that explored the effects on nearly 167,000 people of sitting and watching television. Then they turned to national data collected by the U.S. Centers for Disease Control and Prevention on how much time Americans report sitting and watching TV.
Based on all this data, the researchers calculated that limiting the time Americans spend sitting to three hours or fewer each day would increase the life expectancy of the U.S. population by 2 years. Cutting down TV watching to fewer than two hours each day would bump life expectancy up by another 1.4 years.
Exercise is a good thing, and getting the amount recommended by groups like the CDC, the American Heart Association and the National Cancer Institute -- 30 minutes of moderate to vigorous exercise five times each week -- is a vital part of staying healthy. But Peter Katzmarzyk, the study's lead author and a professor at the Pennington Biomedical Research Center in Baton Rouge, La., said it's becoming clearer that people need to do more.
"It is true that meeting the physical activity guidelines is one of the best things you can do for your health. But on the other hand, there are 23 and a half other hours of the day that we can't ignore," he said.
Alpa Patel, an epidemiologist at the American Cancer Society, agreed that the physical activity guidelines are important, but she said they are based on research conducted over the last 60 years.
"In that time, a lot of what we do in our daily lives has changed," she said. "We've replaced much of what we used to do with sedentary behavior, and we have to understand the implications of that."
It's difficult for scientists to say that your recliner or your television will kill you, and Katzmarzyk said the study doesn't establish a direct cause-and-effect relationship between sitting, TV watching and death. But the evidence suggesting an association between shortened lives and sedentary activities, like TV watching and driving, is piling up. For example, a 2010 study found that the mortality rates were 25 percent lower for people reporting the most physical activity compared with those reporting the least.
But what drives that association is unclear. Dr. Frank Hu, a professor of nutrition and epidemiology at the Harvard School of Public Health, said one possible explanation is that the health effects come not so much from TV watching or driving themselves, but the other things people do during those activities, such as binging on unhealthy snacks or being stressed.
"Those behaviors are very detrimental to our health independent of our physical activity levels," Hu said.
There also seems to be something about sitting itself that is bad for one's health. Studies in both animals and humans have found that sitting leads to changes in resting glucose levels and blood pressure, and that lots of sitting bumps up levels of certain biomarkers of cardiovascular disease and cancer.
"The take-home message is clear: we may not know exactly why sitting is bad for you, but if you reduce the amount of time spent sitting, there are real health benefits," Patel said.
Researchers say the overall message is to move beyond thinking about physical activity as something you do once a day for half an hour. That suggestion has enormous implications for how people currently work, commute and spend their free time.
Katzmarzyk said since many people spend at least eight hours each day sitting at a computer, the workplace is an ideal place to start looking for ways to reform behavior. Patel said changes don't have to be major -- people can get up to talk to colleagues instead of emailing them, or spend a few minutes of their lunch breaks taking a short walk.
And of course, a good place to start making changes is by squeezing the recommended 30 minutes of exercise into every day.
"We have to get folks to understand that doing anything is better than doing nothing," Patel said.
