Running can help slow down cancer growth. A mice study has found that running-related adrenaline surge in mice helped mobilize the natural killer (NK) immune cells in the bloodstream to attack tumors.

Previous studies concluded that NK immune cells can help regulate tumor sizes. The new study focused on how exercise can promote the NK immune cells' tumor infiltration. The genetically modified mice were injected with adrenaline to copy its effect during exercise. The adrenaline helped mobilize the NK immune cells and they move towards the tumors.

"We already know that exercise has an impact on natural killer cell activity, but this is the first time anyone has shown it's directly involved in helping them invade tumors," said Lee Jones from the Memorial Sloan Kettering Cancer Center.

In the study, the mice that ran on the wheels showed a decrease in the tumor growth, which is comparable to a 50 percent decrease in tumor size. The second phase of the study involved taking out the NK immune cells from a group of mice to analyze if its presence at the tumor sites are directly associated with the reduction.

Despite the presence of other immune cells and exercise, the tumors continued to grow at a normal rate with the NK immune cells. When the researchers blocked adrenaline's function, they found a decrease in the tumor-killing benefits of exercise. The research was published in the journal Cell Metabolism on Feb. 16.

Moreover, they found that IL-6, a molecule that signals the immune response, connects the adrenaline-based movement of NK immune cells and its tumor-killing activity.

"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," said senior study author Pernille Hojman from the University of Copenhagen.

Cancer patients often ask how intense they should exercise. The study results suggested that a relatively high intensity exercise can be beneficial in order to produce a surge of adrenaline and recruit the NK immune cells to target tumors.

The tumors in the mice study didn't shrink because of the exercise, rather, the adrenaline-based movement of the NK immune cells helped slow down the growth rate. The findings can lead to improved and new cancer treatments as well as prevention and relapse therapies. However, more research is needed to analyze exercise's effects on longevity and metastatic cancer growth.

Photo: Francisco Osorio | Flickr