New research on mice in Denmark indicates that exercise can reduce the growth of tumours regardless of weight and whether the diet is low or high in fat. A researcher involved in the study says that exercise might have a beneficial anti-cancer effect.
Many epidemiological studies have shown that exercise reduces the risk of developing at least 13 types of cancer, including breast cancer, colon cancer and prostate cancer.
Preclinical studies have also shown that exercise can suppress the growth of tumours.
Now a new study in Denmark has shown that exercise suppresses tumour growth independent of high or normal fat intake and weight.
The study also indicates that the effect does not just result from exercise affecting the immune response.
“The epidemiological data already suggest that exercise protects against the development of cancer independent of body mass index (BMI). However, these results have not been verified in controlled clinical studies, and we therefore wanted to examine the effect further in preclinical studies,” explains a researcher behind the study, Rikke Stagaard, Postdoctoral Fellow, Centre for Physical Activity Research, Rigshospitalet, Copenhagen.
The research, published in Scientific Reports, was led by Pernille Højman, the driving force behind several important studies on how exercise suppresses tumours.
Gave mice a high-fat diet and enabled them to exercise
- One group of mice was fed a standard diet and had access to a running wheel on which they ran 3–4 kilometres every night.
- The second group was fed a standard diet but had no access to the running wheel.
- The third group was fed a high-fat diet that increased their weight and had access to the running wheel.
- The final group was fed a high-fat diet that increased their weight but had no access to the running wheel.
The researchers examined how exercise affects the development of melanoma in normal-weight mice and in overweight mice.
The mice were subcutaneously inoculated with melanoma cancer cells in their flank, in which the cancer was established and subsequently grew into a tumour.
The study used four experimental set-ups.
Then the researchers examined how the tumours in the mice developed and progressed.
“Although we monitored how much the mice ate and how far they ran on the running wheel, we had no control of either, since the mice had free access to both food and the running wheel during the approximately 6 weeks of the trial,” says Rikke Stagaard.
The results from the study showed very clearly that exercise suppressed tumour growth – regardless of whether the mice ate a high-fat or a standard diet.
- Exercise suppressed tumour growth by about 50% in the mice fed a standard diet.
- Exercise suppressed tumour growth by 75% in the mice fed a high-fat diet.
Exercise affects more than just the immune response
The immune response plays a major role in defending against cancer. The researchers therefore also examined how the various scenarios affected the immune response.
Rikke Stagaard explains that obesity can weaken the immune response, whereas exercise can strengthen it.
This part of the study showed that exercise increased the immune response in the tumours from the mice that ate standard food. However, the researchers observed that this effect was attenuated in mice that ate high-fat food.
“The results verify that obesity can suppress the activation of the immune response in connection with cancer. But they also suggest that the beneficial effect of exercise on the development of cancer is not just mediated by the immune cells. So other mechanisms must also be involved when exercise suppresses the development of cancer,” explains Rikke Stagaard, who adds that leptin may have a possible effect.
Leptin is a hormone that helps to regulate appetite, and leptin is often elevated among people who are obese. Studies have also found an association between increased leptin and tumour growth because, among other things, leptin can reduce the cytotoxicity of natural killer cells, which are essential for suppressing tumour growth in (melanoma) cancer.
“It is therefore interesting that our study also found that leptin levels increased in the mice that ate the high-fat food but that exercise reduced this increase. Previous experiments have shown that natural killer cells are crucial for the tumour-suppressing effect of exercise,” says Rikke Stagaard.
Exercise no matter what
Rikke Stagaard says that the study supports previous epidemiological results, but the mechanisms that associate exercise with a tumour-suppressing effect are still not 100% certain.
She indicates that future studies need to investigate the exact mechanisms and should also involve patients.
“Mice and humans differ, but our results further indicate that exercise affects the growth of tumours. Overall, this suggests that jumping on a bike or going for a run could be beneficial, even in a cancer setting. Therefore, regardless of your weight, you should exercise because it might have an advantageous effect,” concludes Rikke Stagaard.
