While the benefits of physical activity in reducing colon and breast cancer are well established, results of studies on exercise and ovarian cancer have been inconclusive. Because ovarian cancer has such a poor prognosis, it is even more important to identify modifiable lifestyle factors that could prevent it.
A new study, published online May 16, 2005 in the International Journal of Cancer, the official journal of the International Union Against Cancer (UICC), found that regular moderate recreational and work-related physical activity may reduce the risk of ovarian cancer. The study is available via Wiley InterScience.
Researchers led by Dr. Sai Yi Pan, of the Public Health Agency of Canada, which is part of the Government of Canada, in collaboration with the Canadian Cancer Registries Epidemiology Research Group, examined data from the Canadian National Enhanced Cancer Surveillance System (NECSS) to study the role of physical activity and ovarian cancer. Self-administered questionnaires were completed and analyzed for 442 ovarian cancer patients and 2,135 controls. Respondents were asked in detail about when and how often they participated in recreational physical activities. Information on occupational activity was also collected in the province of Ontario.
The results showed a decrease in risk of ovarian cancer with high levels of moderate recreational physical activity, but not for vigorous activity. As well women with jobs that required moderate or strenuous activity experienced a reduction in ovarian cancer risk compared with those who worked in sedentary occupations.
Unique to this study was the examination of whether activity-related cancer risk varied by tumor type. Results showed that for moderate recreational activity there was a decreased risk of certain types of ovarian tumors but not for others. No previous studies had examined the relationship between tumor type and physical activity.
Physical activity may decrease ovarian cancer by regulating hormone and growth factor level. Physical activity also has an influence on obesity, which has been shown to increase ovarian cancer risk. "The greater risk reduction among overweight or obese women observed in our study supports the role of physical activity in affecting ovarian cancer risk through its effect on obesity and also implicates that obese women would get more benefit from physical activity against ovarian cancer than lean women," the authors state. They note, however, that the decreased risk with physical activity observed in women with normal weight suggests that other factors also come into play.
Another possibility is that regular moderate physical activity enhances the immune system and improves the antioxidant defense systems both of which may help prevent cancer. This would help to explain why vigorous activity did not show beneficial effect in this study: too much exercise may cause immune suppression and in extreme cases could cause an excessive increase of free radicals and other cellular disturbances.
"In conclusion, our population-based study observed a reduced risk of ovarian cancer among women engaged in higher levels of moderate but not vigorous recreational physical activity," the authors state. They add that the results from Ontario suggest that work-related activity also affords protection against the disease.