Common sense tells us that sitting for long periods of time can’t be very good for us. But a number of recent studies prove sitting to be downright harmful.

As incredible as it sounds, sitting is actually a risk factor for a number of cancers. Last fall, Christine Friedenreich, an epidemiologist at Alberta Services-Cancer Care in Canada, presented findings at the American Institute for Cancer Research Conference that suggested that 49,000 cases of breast cancer, 43,000 cases of colon cancer, 37,200 cases of lung cancer, and 30,600 cases of prostate cancer resulted from prolonged sitting.

In fact, long periods of sitting are predictive of higher mortality from any causes. An American Cancer Society study tracked 123,000 Americans between 1992 and 2006. The men in the study who sat for six hours of their daily leisure time had an overall death rate 20 percent higher than men who sat three hours. In women, the difference was even greater with a 40 percent higher mortality for the sitters.

Is it possible that the higher mortality rate for sedentary people resulted from other factors? After all, the person who sits for most of his leisure time probably doesn’t eat a good diet.

“My impression from reading the research is that there is a direct contribution from sitting,” said Jim McMinn, MD of the McMinn Clinic in Homewood. “For example, one study looked at all the other variables, and they found that sitting for lengthy periods was an independent risk factor.”

The study McMinn refers to looked at 9,000 Australians and found that for each additional hour of sitting, the risk of dying rose by 11 percent. The study author, David Dunstan, controlled for other factors such as age, sex, education, smoking, hypertension, waist circumference, body-mass index, and glucose tolerance status and still found that sitting was an independent pathology affecting mortality.

Apparently, the simple act of sitting causes a number of unhealthy changes in the body. A person’s calorie-burning rate plunges to one-third of what it would be when walking. Insulin effectiveness drops within a single day of sitting and the risk of developing Type 2 Diabetes rises. The enzymes responsible for breaking down lipids and triglycerides plummet, causing good HDL cholesterol to fall.

A recent study of young, fit volunteers found that there was a 40 percent reduction in the subject’s ability to uptake glucose within 24 hours of being sedentary. Researchers have also found that inactivity causes the leg muscles to lose75 percent of the ability to remove harmful lipo-proteins from the blood.

All this is particularly bad news for Americans, as most of us sit at a desk eight or more hours each day. So can we counter this by getting to the gym? Unfortunately not, according to McMinn.

“I’ve always been good about exercising,” McMinn said. “But since sitting is an independent risk factor, you cannot negate that with exercise. For instance, if I sit eight to ten hours a day at work, the fact that I go home and exercise for 30 minutes does not negate ill effects of the sitting.”

So McMinn developed his own solution to the problem. He built a walking desk. “I just put an inexpensive treadmill in my office. It’s a home-construction job. I put a little desktop over it, and when I’m going through my charts, I try to stand at my desk while I’m walking slowly on the treadmill.” McMinn has noticed that he’s more refreshed and vibrant when working this way.

Will this be a wave of the future? It’s possible. Walking and standing desks are becoming fairly commonplace. Even Wal-Mart carries them. If this idea spreads, it could result in a healthier population that might place less strain on the healthcare system.