Physical activity lowers risk of cancer

BRIAN WILLIAMS, anchor: In health news today the headline that got our attention was in USA Today and it read "prolonged sitting linked to breast cancer and colon cancer ." Now, it's not news that being active is part of good health, but is there really a link between sitting and cancer ? Our report between -- from NBC's Anne Thompson .

ANNE THOMPSON reporting: Our car-centered culture, desk-bound workplaces and couch-potato habits make Americans an increasingly sedentary people. But today from a review of 200 cancer studies comes a powerful reason to get up and move.

Dr. SUSAN FRIEDENREICH (Alberta Health Services Epidemiologist): There's quite a consistent evidence that the more physically active these people were, the lower was their risk of cancer .

THOMPSON: Dr. Friedenreich found increased physical activity decreased the risk for breast, colon, endometrial, prostate, lung and ovarian cancers. And for the first time researchers put a number on how many US cancer cases are linked to physical inactivity. Forty-nine thousand cases of breast cancer , 43,000 cases of colon cancer . Putting some pep in your step can help lower key risk indicators , including body fat, inflammation and insulin resistance.

Dr. FRIEDENREICH: Just doing walking on an ongoing basis for at least 30 minutes a day for five days a week is sort of the minimum that we're recommending.

THOMPSON: But in addition researchers say you also have to get out from behind that desk, break up long periods of sitting, they say, by standing or walking, even for a few minutes.

Unidentified Woman #1: I totally believe it. And I personally try to get an hour a day if I can.

THOMPSON: Other doctors call the study reassuring but caution that just moving around more won't prevent cancer .

Dr. MICHAEL BLUTE (UMass Medical School Cancer Center Director): It's probably no guarantee that you won't get cancer , but you can reduce the risk.

THOMPSON: This is the latest in a mind-boggling barrage of cancer studies that often seem to create more conflict than clarity.

Unidentified Woman #2: I kind of weed through it and use what I think is helpful. But it can be confusing at times.

THOMPSON: What is clear is that we are more sedentary and here's some food for thought. The average adult spends more than nine hours a day sitting, and most of that happens at work. That's almost two-thirds of his or her waking

hours. Brian: So getting up is good, just not perhaps right now. Anne Thompson .

WILLIAMS: Not at this moment.

THOMPSON: Anne , thanks. And up next

WILLIAMS: