Exercise May Reduce Cancer Risk by Starving Tumours of Energy, Yale Study Finds

Growing evidence links increased exercise with a lower cancer risk, but the reason for this connection has remained unclear.

A new study in mice points to a metabolic change that may allow muscle cells to use more fuel while depriving cancer cells of the energy they need to grow.

Yale study examines exercise and tumour metabolism

Researchers at Yale University investigated metabolic responses in mice carrying breast cancer or melanoma tumours. The animals were divided according to their diet and levels of physical activity.

Using molecular tracers, the team tracked where glucose was metabolised in the mice. They found that active animals appeared to divert energy and fuel away from cancer cells and towards their muscles.

After four weeks, mice fed a high-fat diet that exercised regularly had substantially smaller tumours than inactive animals on the same diet.

"Obese mice which underwent four weeks of voluntary wheel running after tumor injection exhibited nearly a 60 percent reduction in tumor size," Yale University physician-scientist Brooks Leitner and colleagues report in their published paper.

The researchers also found 417 metabolism-related genes that were expressed differently in active mice than in sedentary but lean mice.

Together, these molecular shifts indicated that the tumours had moved into a high-stress survival state.

Exercise, glucose and cancer cell growth

Exercise particularly reduced activity of a protein called mTOR in the animals’ tumours. This may be important for limiting tumour growth and could help guide the search for new treatments.

The findings indicate that glucose is "a key metabolic mediator of the tumor-suppressive effects of exercise", according to the researchers.

However, they also note that "this metabolic relationship and the ability for exercise to slow tumor growth may depend on exercise duration."

Cancer is a complex disease in all of its forms, involving numerous mechanisms in tumour development and growth. Going to the gym alone will not prevent cancer.

Physical activity may help prevent cancer

Even so, physical activity may be an important factor in improving the chances of preventing the disease from developing. The researchers also discovered that obese mice which exercised for two weeks before tumours were implanted developed smaller tumours than sedentary mice.

"These data highlight the importance of a nuanced, systemic view of the metabolic effects of exercise in cancer," Leitner and colleagues write.

It is encouraging that the same mechanisms seem to operate in two tumour types, suggesting that exercise benefits may not be confined to one form of cancer.

Scientists must still establish whether the same processes occur in humans before knowing if these results apply to people.

The team now wants to extend its research to human cancer tumours, with more closely defined exercise types and durations. This should reveal more precisely how remaining active may help protect against cancer.

"Examination of the role of fitness on the molecular pathways altered by exercise may uncover new therapeutic targets in precision oncology, particularly in patients who cannot tolerate exercise," the researchers conclude.

The research was published in PNAS.