The surge of adrenaline during a high-intensity workout may help certain immune cells slow cancer growth, an animal study published Tuesday in Cell Press suggests.

Researchers found that mice that spent their free time on a running wheel were 50 percent better at shrinking their tumors than their less-active counterparts, Science Daily reported.

"It is known that infiltration of natural killer (NK) immune cells can control and regulate the size of tumors, but nobody had looked at how exercise regulates the system," senior study author Pernille Hojman,of the University of Copenhagen, said in a news release.

For their research, the team injected mice with adrenaline to mimic the increase seen during exercise and saw that NK cells targeted tumors. Then, they studied mice depleted of NK cells and found that, even with exercise and other immune cells, cancerous tumors grew at a normal rate.

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Scientists found that IL-6, an immune signaling molecule, was the link between adrenaline-dependent mobilization of NK cells and tumor infiltration, Science Daily reported, finding that adrenaline specifically hails IL-6 sensitive NK cells and the IL-6 molecules help guide immune cells to tumors.

"That was actually a big surprise to us," Hojman said, noting that IL-6 and its role in tumor biology can be a controversial topic. "In this study we show that the exercise-induced IL-6 seems to play a role in homing of NK cells to the tumor and also in the activation of those NK cells."

Study authors said their findings were promising, but they noted more research needed to be done on the effect exercise may have on metastasis and longevity. They also noted the same study needed to be conducted on humans.

"As someone working in the field of exercise and oncology, one of the main questions that cancer patients always ask is: How should I exercise? Can we do anything?" Hojman said. "While it has previously been difficult to advise people about the intensity at which they should exercise, our data suggest that it might be beneficial to exercise at a somewhat high intensity in order to provoke a good epinephrine surge and hence recruitment of NK cells."