Mouse-based study shows exercise decreases cancer incidence, slows tumor growth

When you're pounding along an icy pavement or sweating through a gym workout, you try to remind yourself of the many health benefits of exercise. Between gasps, you can say that a healthy, fit lifestyle helps prevents obesity, a worldwide problem of increasing magnitude that has been linked to cardiovascular disease and diabetes. But here's one more—exercise may decrease cancer incidence and slow the growth rate of tumors. That's the conclusion of a mouse-based study published in Cell Metabolism by Line Pedersen, Pernille Hojman, and colleagues at the University of Copenhagen reporting that training mice regularly on a wheel (the mouse version of a treadmill) decreased the growth of multiple types of tumors, including skin, liver, and lung cancers. Furthermore, mice that exercised regularly had a smaller chance of developing cancer in the first place. The beneficial effects of running went beyond tumor formation and growth, extending to cancer-associated weight loss, a process termed cachexia that is seen in cancer patients. Mice that exercised regularly showed no signs of cancer-associated weight loss in the researchers' lung cancer mouse model.

The researchers say they identified several factors behind the anti-tumor effects of exercise. These anti-cancer effects are linked to the release of adrenaline (also called epinephrine), a hormone that is central to the "fight-or-flight" response. Adrenaline production is known to be stimulated by exercise. The researchers say that, the production of adrenaline results in a mobilization of immune cells, specifically one type of immune cell called a Natural Killer (NK) cell, to patrol the body. These NK cells are recruited to the site of the tumor by the protein IL-6, secreted by active muscles. The NK cells can then infiltrate the tumor, slowing or completely preventing its growth. Importantly, the researchers note that injecting the mice with either adrenaline or IL-6 without the exercise proved insufficient to inhibit cancer development, underlining the importance of the effects derived only from regular exercise in the mice.

Along with offering encouragement for joggers and lap swimmers everywhere, this research points to the use of NK cells as a potential therapeutic strategy for multiple tumors.