By Gretchen Reynolds, New York Times

The relationship between exercise and cancer has long both intrigued and puzzled oncologists and exercise physiologists.

Exercise is strongly associated with lowered risks for many types of cancer. In epidemiological studies, people who regularly exercise generally prove to be much less likely to develop or die from the disease than people who do not. At the same time, exercise involves biological stress, which typically leads to a short-term increase in inflammation throughout the body. Inflammation can contribute to elevated risks for many cancers.

Now, a study in mice may offer some clues into the exercise-cancer paradox. It suggests that exercise may change how the immune system deals with cancer by boosting adrenaline, certain immune cells and other chemicals that, together, can reduce the severity of cancer or fight it off altogether.

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