According to two new studies proper exercise may provide some protection from skin and bowel cancers.
Although the two studies were conducted on laboratory animals, the researchers claim to have traced the mechanism that could cause this protective effect.
One study conducted at Rutgers University, New Jersey, focused on skin cancer in mice and 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.
Lead study researcher Dr. Allan Conney, Garbe Professor of Cancer and Leukemia Research, suggests that exercise could actually increase the physiological cell-death process and hence these mice showed delayed development of tumors although they were at significant risk.
The second study at the University of Wisconsin-Madison 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.
Lead researcher Dr. Lisa Colbert suggests that a negative energy balance, which is produced by increasing energy output through exercise, could be the reason for the inhibition of polyps.
Dr. Colbert says there were on average 16 polyps per mouse in the exercising mice compared to 22 polyps in the control mice, a decrease of 25%.
Conney believes the studies may be the first to suggest a cell suicide mechanism effect linked to voluntary exercise and the development of cancer, which she says deserves further investigation.
The studies are published in the May 13 issue of the journal "Carcinogenesis".