By: Ergolog

Every session of fairly intensive physical exercise works like a mini chemotherapy course, we wrote recently. Physical exertion transforms the body into a hostile environment for cancer cells. An animal study that Danish researchers published in 2016 in Cell Metabolism tells how.


The researchers, who work at the University of Copenhagen, gave a group of mice unlimited access to a treadmill that the animals ran in for about 4-7 kilometres every day. The human equivalent of this amount of exercise would be about an hour working out in the gym.

After the mice had been running every day for four weeks they were given an injection containing aggressive cancer cells – B16F10 melanoma cells. Two weeks later the Danes examined the mice.

The mice in the control group did not run.


The mice that had run [EX] had a much lower tumour volume than the mice in the control group [CON]. The mice that had run also had fewer metastases in their lungs.

The cells in the tumours in the mice that had run produced more interleukin-1-beta, interleukin-6, interleukin-10 and TNF-alpha than the cells in the tumours of the inactive animals. These inflammatory factors are ‘bad’ in healthy cells, but ‘good’ in cancer cells. They activate immune cells. And those immune cells, as you can see in the figure on the right below, were also found in high concentrations in the tumours of the active mice.

Physical exercise led above all to an increase in the number of Natural Killer cells [NK cells], as the figure on the right shows. Natural Killer cells are the immune system’s shock troops. They are the first to attack any faulty cells or pathogens circulating in the body.

“The potential of tumor-infiltrating NK cells is still being unravelled,” wrote the Danes. “NK cells are part of the early innate immune response and can activate other immune cells through secretion of interferon-gamma. Thus, a key action of NK cells is to deliver the initial ‘spark’ that activates other cell types of the immune system.”

Interleukin-6 in particular could be important, the Danes suspect. Interleukin-6 is released if muscles are subjected to intensive exercise, and Natural Killer cells have receptors for interleukin-6. And hey presto, when the researchers repeated their trials and injected the active mice with an antibody that deactivates interleukin-6 [Anti-IL6], the cancer-inhibiting effect of exercise disappeared.

But that wasn’t the whole story. Administering synthetic interleukin-6 allone did not have a cancer-inhibiting effect, the Danes discovered in a different series of tests. Sometyhing elkse was needed as well to activate the Natural Killer cells: the natural pep hormone adrenalin and its relative noradrenalin, the researchers discovered. If they blocked those hormones by giving the mice the beta-blocker propranolol, then the cancer-inhibiting effect of exercise disappeared completely. [Figure]

It’s the combination of interleukin-6 and adrenalin that activates the Natural Killer Cells to attack tumours.


Physical exercise protects against cancer. This is certainly true of more intensive forms of exercise, in which the muscles produce large amounts of inflammatory factors and the adrenals secrete large amounts of adrenalin. Although this animal study does not show that physical exercise actually stops cancer, the Danes do suggest that physical exercise can strengthen the effect of conventional cancer therapies.

Cell Metab. 2016 Mar 8;23(3):554-62.