Exercise and Cancer
From EurekAlert!, another way in which exercise helps healthy longevity: "Men who exercise often are less likely to die from cancer than those who don't exercise ... In the study, the researchers looked at the effect of physical activity and cancer risk in 40,708 men aged between 45 and 79. Over the seven year period of the [study], 3,714 men developed cancer and 1,153 died from the disease. Men who walked or cycled for at least 30 minutes a day had an increased survival from cancer with 33 per cent, than the men who exercised less or did nothing at all. The researchers also found that a more extensive programme of walking and cycling for between 60 and 90 minutes and a day, led to a l6 per cent lower incidence of cancer. But these activities only led to a five per cent reduction in cancer rates among the men who walked or cycled for 30 minutes day, a finding which could be due to chance." One might speculate that this has to do with maintaining a more capable immune system (which can destroy cancer at the earliest stages) and losing the visceral fat, thereby reducing chronic inflammation. Less biochemical damage to the body's vital systems means a lower chance of runaway failure in your cells.
Link: http://www.eurekalert.org/pub_releases/2008-05/ki-ecc052908.php