How many times have you heard/read it - "Moderate exercise is good for you
Half an hour a day (average) of moderate exercise (bike riding, brisk walking, serious dancing, etc.) reduces the incidence of intestinal, endometrial, colon, breast and lung cancers.
Why, you ask? Let me tell you - apparently because moderate exercise kicks up the immune system. A well-tuned immune system, running along efficiently, does a better job of recognizing rogue cells that turn cancerous before they can become tumors. Maybe, if it turns out that viruses are involved in more cancers than we know about, a top-notch immune system destroys them before they can do their dirty work. Maybe it's some other mechanism that we'll find out about in the future.
For now, the recommendation I can give is to move a little more. I'm trying to get my Mother In Law to walk around the local indoor shopping mall. I'm suggesting that my mother take stairs and not the elevator. Both my Mother and Mother-in-law are in their 90's, so 'moderate exercise' for them is WAY different than 'moderate exercise' for me. The main point is - get off your butt!