If you spend nearly all your working day sitting at a desk, as 50 to 70 percent of Americans do, you may be shortening your life.
"Sitting is the kiss of death," said Ron DeAngelo, director of sports performance training at UPMC's Center for Sports Medicine. "We weren't designed to sit. In prehistoric days, we never sat."
People who sit for most of the day are 54 percent more likely to get a heart attack than people who sit for less than three hours a day, according to a study published in July by researchers at Louisiana State University. Active people live about two years longer.
"Sitting too much is not the same as exercising too little," said Marc Hamilton of LSU's Pennington Biomedical Research Center, the lead researcher. "Sitting does completely different things to the body."
None of them are good. When we sit for prolonged periods, good genes are turned off, bad genes are turned on, he said. Sitting shuts down the circulation of lipase, a fat-absorbing enzyme, researchers at the University of Missouri found. The leg muscles responsible for standing almost immediately lost more than 75 percent of their ability to remove harmful lipo-proteins from the blood, Dr. Hamilton found in his study of rats forced to be inactive.
Sitting is more deadly for women. American Cancer Society researchers studied the records of 123,216 people enrolled in the Cancer Prevention II study between 1992 and 2006. Men who sat for six or more hours a day were 18 percent more likely to die during that period than men who sat for less than three hours, they found. Women who sat for six or more hours were 37 percent more likely to die.
Lack of mobility makes us older faster, said Vonda Wright, director of the Performance and Research Initiative for Masters Athletes at UPMC Sports Medicine.
"Down to a very cellular level we are designed to move," Dr. Wright said. "When we are moving, our bodies maintain the functions that keep us moving."
But when we stop moving for extended periods, our natural defenses against disease weaken. We get sick more often; we stay sick longer. Chronic disease is the principal cause of aging, Dr. Wright said.
You're chained to your desk during the day, but most days you exercise before or after work. You don't smoke, you eat right. Surely these statistics don't apply to you.
Alas, they do. Even if you exercise, if you sit for more than 11 hours a day, you are up to 40 percent more likely to die within three years than someone who sits for less than four hours, according to an Australian study last year.
When we sit, the rate at which we burn calories plunges to a third of what it is when we're walking around. Dr. Michael Jensen of the Mayo Clinic found that those who gained weight in his study ate no more than those who didn't -- but they sat for two hours longer each day.
Sitting for prolonged periods is the principal cause of low back pain, Mr. DeAngelo said. When we sit, our lower back supports more than half our body weight. Sitting causes the curve in our lumbar (lower) spine to flatten, which puts pressure on our discs, ligaments and muscles.
For Mr. DeAngelo, the solution is obvious. Don't sit.
"The No. 1 thing I recommend is to change from a seated desk to a standing desk," he said.
When you stand, you burn twice the calories as when you sit. Standing facilitates circulation of blood, which sitting impedes.
Most who've made the switch to stand-up desks say they're mentally sharper. This is because when you stand, more blood is pumped to your brain.
Bill Elm, 57, president of software designer Resilient Cognitive Solutions, went to Mr. DeAngelo for help with his workouts, but "all the sitting I was doing was causing the problem faster than Ron could fix it." He's experienced a boost in his energy level at work since switching to a stand-up desk two years ago.
You can buy a stand-up desk from Buddy Products for $185.68 or spend thousands of dollars for desks that come with a treadmill or a recumbent cycle. If you've got a treadmill, TrekDesk will sell you a stand-up desk to fit it for $479. FitDesk sells a compact pedal desk for $249.99.
Standing for prolonged periods isn't so good for you either, cautions Alan Hedge, who directs ergonomics research at Cornell University. Standing is "more tiring, dramatically increases the risks of carotid atherosclerosis because of the additional load on the circulatory system, and it increases the risks of varicose veins," he said.
What's ideal is to stand for a while, then sit for a while. The most popular stand-up desks are adjustable. Ergo Depot offers four models, beginning at $579.99. Geekdesk's adjustables start at $749.
Workers who were given sit-stand desks reduced their sitting time by 66 minutes a day, and reported a 54 percent reduction in neck and upper back pain, according to a study in Minneapolis last year.
Most of the baneful effects of prolonged sitting can be mitigated if, every 20 minutes to an hour, you stand up, stretch, and move around. Stretching is important because muscles -- the hamstrings especially -- shorten and tighten when you sit, Mr. deAngelo said.
The more, and more vigorously you move on these little breaks, the greater the benefit. Cardiologist Raymond Benza walks the stairs of the south tower at Allegheny General Hospital twice most days. Since he started, "my overall feeling of well being really soared."
But "research shows you don't need to do vigorous exercise to get benefits," professor Hedge said. "Just walking around is sufficient."
Dona Wilfong, a nurse at West Penn Allegheny Health System's STAR Center, walks around her office at least once an hour and takes a longer walk during her lunch break. "I get burned out if I sit for a long time," she said.
If your job doesn't permit you to leave your desk, you can get significant benefits just by standing for a minute or two. When you stand, the big muscles in your legs and back contract, which speeds production of enzymes that break up fat in the bloodstream.
Dr. Wright gave each of the secretaries in PRIMA an exercise ball on which to sit for part of the day. Sitting on a ball strengthens core muscles. Because it is unstable, you constantly have to make small adjustments in your position to keep from falling off. That's enough to mitigate the worst effects of sedentariness, and you'll burn about 30 more calories a day.
Sitting on an exercise ball can be tricky. The Gaiam Balance Ball Chair (which has a back rest) provides a happy medium. You can buy one at Dick's Sporting Goods for $99.99. And whatever you sit on, fidget, Dr. Wright advises. Any activity makes sitting less deadly.
Jack Kelly: firstname.lastname@example.org or 412-263-1476. First Published October 15, 2012 4:00 AM