I have a confession to make.

As soon as I finished reading the Annual Report to the Nation recently, I got up from my desk and took a walk for 20 minutes.

What, might you ask, compelled me to do this?

The answer is what made me take a walk is the same reason I am writing this follow-up commentary. Sitting at my desk all day may kill me. It may be doing the same for you.

I don’t know how many of us are aware that physical inactivity-apart from being overweight or obese-is an independent risk factor for cancer. In plain terms, you may think you are healthy because your body weight is normal, but in reality you may be one of those folks who also sit at a desk like I do for 8-10 or more hours a day, or spend your life traveling in cars and airplanes. If you are, then your risk of cancer is increased, independent of how much you weigh. And there are now suggestions that even engaging in vigorous physical activity doesn’t mitigate the adverse impact of sitting on your you-know-what for hours every day. (Other research that I have commented on previously shows clearly that when it comes to deaths from any cause, your risk of death is greater if you sit for long periods of time every day regardless of how much physical activity you do.)

If you pay attention to your life, I suspect most of us would be shocked to find out how many hours we spend sitting, with the only breaks we take to go to lunch or you-know-where a couple of times a day or maybe going to the coffee pot or the proverbial water cooler.

Anyway, I think you get the point: we spent a lot of time sitting down and very little in physical activity. The net result is that you are at an increased risk of getting several cancers. So the message is: get up and get moving-even if it means walking around your place of work from time to time or walking down the hall to chat with a colleague instead of sending an email or making a phone call.

Why all this concern about physical inactivity? Because as the authors of the Annual Report note, results of extensive literature reviews show that a lack of sufficient physical activity has been associated with a 30-40% increased risk of colon cancer, postmenopausal breast cancer and endometrial cancer. And we can’t lose sight of the fact that being physically inactive helps to put the pounds on and keep them there, which also leads to increases in risk for a whole host of other cancers as well.

Let’s read what the researchers wrote about the “state of the nation” when it comes to physical activity in the Annual Report:

On the basis of data … in 2009, 75% of US high school boys and 89% of high school girls did not engage in recommended levels of physical activity; 17% of boys and 30% of girls were considered physically inactive. The prevalence of physical inactivity increased with grade level. In analyses by racial and ethnic group, the prevalence of physical inactivity was highest among non-Hispanic black boys and girls.

On the basis of data … in 2008, 53% of US men and 60% of US women did not engage in recommended levels of aerobic activity; more than one-third were considered physically inactive. The prevalence of physical inactivity increased with age and was highest among Hispanic men and non-Hispanic black women. Adults with a college degree had the lowest prevalence of physical inactivity.

The report goes on to say:

The International Agency for Research on Cancer concluded that from one-quarter to one-third of common cancers in industrialized nations were caused by the joint effect of excess weight and lack of sufficient physical activity. The World Cancer Research Fund/American Institute for Cancer Research concluded that approximately one-third of common cancers in the United States could be prevented by following healthy patterns of physical activity and diet, including maintaining a healthy weight…Despite some differences in the magnitude of the estimates, researchers agree that excess eight and lack of sufficient physical activity are important, avoidable causes of cancer in the United States and other industrialized nations.

Here is the clincher, as noted in the Report:

 Some research suggests that physical activity may influence cell cycle changes differently than calorie restriction…Emerging research indicates that, independent of physical activity, the amount of time spent in sedentary behaviors, such as sitting, may adversely affect health outcomes, including cancer.

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The net results are that increased weight and physical inactivity have led to higher incidence rates for a number of cancers associated with these risk factors. Postmenopausal breast cancer, kidney cancer, pancreatic cancer, uterine cancer and adenocarcinoma of the esophagus have increased in frequency in the United States. Colorectal cancer would have probably been on the list as well, were it not for the fact that more people are getting screened or having polyps removed before they become cancerous.

As I mentioned in yesterday’s blog, physical inactivity also places a direct financial burden on health care costs in this country. In 1995, research showed that inactivity, independent of obesity, cost this country 2.4% of total US health care expenditures. I can only imagine what the amount/percentage would be today.

So here we are, learning more constantly about the impact of overweight, obesity and physical activity on increasing our risks of cancer. And sitting for long periods of time-and apparently even if we are physically active at certain times of our day-is an independent risk factor for cancer.

I suspect there are some of us who are just getting comfortable with the idea that cancer has joined other chronic diseases such as high blood pressure, stroke, diabetes and heart disease (among others) where overweight and obesity increases risk. Now I think it is time for us to consider the fact that how we spend our days-whether sitting or walking around from time to time-is independently related to increasing cancer risk.

So what can we do?

Well, for starters, we can get off our duffs and walk more. Take a walking break instead of a coffee break. Walk a bit further in the parking lot. Walk more around the streets where you live. Do something besides sitting in your chair at your desk for hours on end, or on the sofa at home watching TV at night.

We also have to realize-as pointed out in the report-that this is not just about us as individuals. It is about us as communities, creating environments that encourage healthy lifestyles, making better choices about our diets and our activities, making certain that all of our communities have access to affordable fresh fruits and vegetables and safe places to walk or for kids to play. We need to make certain our children have adequate time and facilities for physical activity, and that we create a culture of health where better behaviors and better lifestyles lead to a healthier country-with less disease and for certain less cancer.

This is no small task, my friends. We are clearly on a path as a nation in the opposite direction from where we need to be. That’s what the research and the statistics tell us. But I for one am an optimist that we can make change, for ourselves, our families, our colleagues, our communities and our nation.

And now, to celebrate my newfound awareness, I am going to go for a walk and perhaps save my body from this slow, insidious deterioration. Maybe you should do the same.

J. Leonard Lichtenfeld is deputy Chief Medical Officer for the national office of the American Cancer Society. He blogs at Dr. Len’s Cancer Blog.

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