The Hazards of the Couch

Many of us sit in front of a computer for eight hours a day, and then go home and head for the couch to surf the Web or watch television, exchanging one seat and screen for another. Even if we try to squeeze in an hour at the gym, is it enough to counteract all that motionless sitting?
A mounting body of evidence suggests not.
Increasingly, research is focusing not on how much exercise people get, but how much of their time is spent in sedentary activity, and the harm that does.

The latest findings, published this week in The Journal of the American College of Cardiology, indicate that the amount of leisure time spent sitting in front of a screen can have such an overwhelming, seemingly irreparable impact on one’s health that physical activity doesn’t produce much benefit.
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One possible mechanism, demonstrated in animal studies, is that being sedentary may affect lipid metabolism. Prolonged inactivity appears to sharply reduce the activity of an important enzyme called lipoprotein lipase, which is responsible for breaking down circulating blood lipids and making them available to muscles for energy, Dr. Stamatakis said. Lowered enzyme activity leads to higher levels of fats and triglycerides in the blood, and to a higher risk of cardiovascular disease. Exercise has very little impact on the enzyme’s activity, he said.
Extended sitting may also lead to high levels of low-grade inflammation, which can also lead to heart disease, Dr. Stamatakis said. A marker of low-grade inflammation called C reactive protein was about three times higher in the study participants who spent the most time slouched in front of a screen.