By pooling the results of over 50 studies, researchers in the US confirmed and brought up to date the evidence of a strong link between physical exercise and colon cancer whereby men and women who exercise more have a lower risk of developing the disease, and they also firmed up the estimates of the size of risk.
The meta-analytical study was the work of lead author Dr Kathleen Y Wolin of the Department of Surgery, Washington University School of Medicine in St Louis, Missouri, and colleagues, and is published in the advanced online 10 February issue of the British Journal of Cancer.
The authors wrote that although a link between physical activity and colon cancer risk is well established, in that more physical activity is linked with lower disease risk, there is no formal estimate of the size of this risk and how it varies that is supported by recent studies.
For this study, they analyzed a total of 52 research papers going back to 1984. They left out any studies that combined colon and rectal cancer because there is no evidence that exercise affects rectal cancer and there would be a danger that including rectal cancer would understimate the size of the link between physical activity and colon cancer alone.
They analyzed the data by sex and study design: thus arriving at separate and combined estimates for men and women and different types of studies, such as case control and cohort studies.
The results showed that:
- Comparing people who did the most exercise with the ones who did the least, the ones who did the most had a 24 per cent lower risk of developing colon cancer.
- For men, the figure was also 24 per cent, for women it was 21 per cent.
- Findings from case-control studies were stronger (31 per cent lower risk of colon cancer for those who exercised the most compared to those who exercised the least) that those from cohort studies (17 per cent lower risk).
Case control studies make comparisons between people with the disease and counterparts that do not have the disease (the controls). Cohort studies follow a group over a period of time and either make comparisons within the group or with another group that is representative of the general population.
The authors concluded that:
“This study confirms previous studies reporting an inverse association between physical activity and colon cancer in both men and women, and provides quantitative estimates of the inverse association.”
Wolin, a cancer prevention and control expert with the Siteman Cancer Center at Barnes-Jewish Hospital and Washington University. explained to the press:
“What’s really compelling is that we see the association between exercise and lower colon cancer risk regardless of how physical activity was measured in the studies.”
“That indicates that this is a robust association and gives all the more evidence that physical activity is truly protective against colon cancer,” she argued.
Colorectal cancer is the third most common type of cancer. More than 100,000 Americans are diagnosed with colon cancer and about 40,000 with rectal cancer every year. The findings of this study would suggest that more than 24,000 fewer cases of colon cancer would be seen among Americans every year if they were to exercise a lot more.
Wolin and colleagues found that it didn’t matter what form the exercise took: whether it was a leisure activity such as jogging or swimming, or occupational such as walking or digging; it had the same effect for both men and women.
Wolin said:
“The beneficial effect of exercise holds across all sorts of activities.”
“There is an ever-growing body of evidence that the behavior choices we make affect our cancer risk. Physical activity is at the top of the list of ways that you can reduce your risk of colon cancer,” she added.
“Physical activity and colon cancer prevention: a meta-analysis.”
K Y Wolin, Y Yan, G A Colditz and I-M Lee.
Br J Cancer advance online publication, February 10, 2009.
doi:10.1038/sj.bjc.6604917
Sources: Journal abstract, University of Maryland Medical Center.
Written by: Catharine Paddock, PhD