Here’s some promising news that would gladden the hearts of our rodent friends if they could read: New research shows that cancerous tumors grow more slowly in mice that run more. Scientists now intend to test the effect in humans.

In a study carried out by the University of Copenhagen, researchers found that tumors shrink 50 per cent faster in mice given access to a running wheel, as compared to inactive animals. The results are published in the scientific journal Cell Metabolism.

Scientists studied the effects of a four-kilometer daily run in mice with cancer and found that the regime shrunk the size of their tumors by 50 to 60 per cent. “It doesn’t apply to just one specific type of cancer, but generally [to many cancers]. We see it especially in malignant melanoma, liver, and lung cancer,” said co-author Pernille Højman, a postdoc at Center for Physical Activity Research, Denmark.

The exercise-related surge in adrenaline helps move the cancer-killing immune cells towards the tumor, scientists believe. These cells can recognize viruses and bacteria, and also tumor cells. It was also found that exercise makes muscles release a specialized signaling substance that can help guide the immune cells towards the tumors. The activated muscles produce IL-6, a chemical that helps the immune cells attack the tumor.

“The cells enter the blood stream with the adrenaline, but they also need to enter the tumour itself. Here, IL-6 is essential. We’ve found that aerobic exercise is a kind of switch that can turn the immune system to fight against the cancer,” said Højman.

As heartening as that sounds, it’s essential that the workout hits a certain level of intensity to achieve this effect; a simple, short low-energy jog is not enough. Ideally, patients should exercise hard or long enough to the extent that they become out of breath and are unable to hold a conversation, affirms Højman. Depending on how fit you already are, this could be anything from 20 minutes to an hour of intense exercise. In fact, Højman believes that patients who are in bad health need not be deterred, as those who are already in good physical shape actually produce IL-6 more slowly than less-fit patients.

She is also “fairly optimistic” that the results can be applied from mice to humans. “The first step will be to test how immune cells respond in healthy people, and then we would like to proceed with cancer patients later this spring,” she concludes. If successful, the study should be a hopeful way out for patients looking for inexpensive ways to manage their cancer.

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