How might exercise help reduce the risk of lung cancer?

In a handful of studies, there was a clear link between an increased level of physical activity and a decreased risk of lung cancer. In the College Study, for instance, moderately active alumni had a 21 percent reduction in the risk of lung cancer compared with inactive alumni. The highly active alumni enjoyed a 61 percent reduction in risk. Also, men over 60 achieved the same benefits from exercise in terms of reduced risk of lung cancer as younger men.

Findings such as these are plausible. If you exercise, you're much less likely to smoke, and again, smoking is the primary cause of lung cancer. But more significantly, among the alumni, active nonsmokers also had a lower risk of lung cancer compared with inactive nonsmokers; likewise, physical activity also was found to provide some protection from lung cancer even for those who indulged in the noxious habit. Thus, physical activity may offer protection from lung cancer through some mechanism other than control of the nicotine habit. Just what that mechanism might be is open to considerable debate, but one possibility is increased ventilation of the lungs. When you exercise, you breathe more deeply and rapidly. This may help flush the lungs of carcinogens, even those found in cigarette smoke.