Published in the journal "Carcinogenesis", one study found that female mice that had 24-hour access to running wheels and were exposed to ultraviolet B light (UVB) took longer to develop skin tumours, developed fewer and smaller tumours, and had decreased amounts of body fat compared to mice that did not have access to running wheels. The second study looked at the development of pre-cancerous polyps in the intestines of male mice and discovered that voluntary exercise and a restricted diet reduced the number and size of polyps and improved survival.
Dr Allan Conney, Garbe Professor of Cancer and Leukemia Research and Director of the Susan Lehman Cullman Laboratory for Cancer Research at Rutgers University, New Jersey, USA, is one of the authors of the skin cancer study. He said that programmed cell death (apoptosis), triggered by exercise, might explain why the running wheel mice did better.
"Preliminary indications from follow-up work in the laboratory suggest that voluntary exercise enhances UVB-induced apoptosis in the skin, and that it also enhances apoptosis in UVB-induced tumours. So, although UVB is triggering the development of tumours, exercise is counteracting the effect by stimulating the death of the developing cancer cells.
"Our studies may be the first to suggest an apoptotic mechanism for the effect of voluntary exercise in the development of cancer. In addition, we found that voluntary exercise decreased body fat and that the number of tumours decreased with decreasing amounts of fat. This effect may also play an important role in the mechanism and warrants further investigation, bearing in mind the growing rates of obesity in the Western world, particularly in the USA and UK," he said.