Health: Is Sitting a Lethal Activity?

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Why do some people who consume the same amount of food as others gain more weight? After assessing how much food each of his subjects needed to maintain their current weight, Dr. Levine then began to ply them with an extra 1,000 calories per day. [Surprisingly] some of his subjects packed on the pounds, while others gained little to no weight.

We measured everything, thinking we were going to find some magic metabolic factor that would explain why some people didn't gain weight, explains Dr. Michael Jensen, a Mayo Clinic researcher who collaborated with Dr. Levine on the studies. But that wasn't the case. Then six years later, with the help of the motion-tracking underwear, they discovered the answer. The people who didn't gain weight were unconsciously moving around more, Dr. Jensen says. They hadn't started exercising more — that was prohibited by the study. Their bodies simply responded naturally by making more little movements than they had before the overfeeding began, like taking the stairs, trotting down the hall to the office water cooler, bustling about with chores at home or simply fidgeting. On average, the subjects who gained weight sat two hours more per day than those who hadn't.

Exercise is not a perfect antidote for sitting, says Marc Hamilton, an inactivity researcher at the Pennington Biomedical Research Center.

The posture of sitting itself probably isn't worse than any other type of daytime physical inactivity, like lying on the couch watching Wheel of Fortune. But for most of us, when we're awake and not moving, we're sitting. This is your body on chairs: Electrical activity in the muscles drops — the muscles go as silent as those of a dead horse, Hamilton says — leading to a cascade of harmful metabolic effects. Your calorie-burning rate immediately plunges to about one per minute, a third of what it would be if you got up and walked. Insulin effectiveness drops within a single day, and the risk of developing Type 2 diabetes rises. So does the risk of being obese. The enzymes responsible for breaking down lipids and triglycerides — for vacuuming up fat out of the bloodstream, as Hamilton puts it — plunge, which in turn causes the levels of good (HDL) cholesterol to fall.

Over a lifetime, the unhealthful effects of sitting add up. Alpa Patel, an epidemiologist at the American Cancer Society, tracked the health of 123,000 Americans between 1992 and 2006. The men in the study who spent six hours or more per day of their leisure time sitting had an overall death rate that was about 20% higher than the men who sat for three hours or less. The death rate for women who sat for more than six hours a day was about 40% higher. Patel estimates that on average, people who sit too much shave a few years off of their lives.

Sitting, it would seem, is an independent pathology. Being sedentary for nine hours a day at the office is bad for your health whether you go home and watch television afterward or hit the gym. It is bad whether you are morbidly obese or marathon-runner thin. Excessive sitting, Dr. Levine says, is a lethal activity.

For more, see Is Sitting a Lethal Activity? by James Vlahos, April 14, 2011 at NYTimes.com.