Exercise protects against cancer (in mice)
Exercise can protect against cancer, new findings from two animal studies suggest.
One showed that physically active mice with 24-hour access to running wheels took longer to develop skin tumours. The other found that exercise and a restricted diet reduced the number of pre-cancerous bowel growths in mice.
In the first experiment, mice were exposed to ultraviolet B rays, one of the harmful components of sunlight. Professor Allan Conney, who led the research at Rutgers University, New Jersey, USA, suspects that exercise increases levels of cell suicide, or apoptosis.
The programmed death of defective cells is one way the body protects itself against cancer.
"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," said Prof Conney.
"So, although UVB is triggering the development of tumours, exercise is counteracting the effect by stimulating the death of the developing cancer cells."
The study also showed that the number of tumours decreased with fat reductions resulting from exercise. The bowel cancer study was led by Dr Lisa Colbert, from the University of Wisconsin-Madison, USA.
Her findings suggest that a negative energy balance, produced by raising energy output while restricting calorie intake, helps inhibit polyps that lead to bowel tumours. Both studies were published in the journal Carcinogenesis.
Evidence from population studies already has already indicated that physically active people are less likely to suffer bowel cancer. In the skin cancer study, running reduced the number of non-malignant tumours by 34%. Exercise also reduced the size of malignant tumours in one test by 73%.
"On average there were 16 polyps per mouse in the exercising mice compared to 22 polyps in the control mice, a decrease of 25%," said Dr Colbert.