Getting plenty of physical exercise cuts your chance of getting colon cancer by almost a quarter, the latest research has confirmed. But we still don't know how intense the exercise has to be to reduce the risk by this much - a brisk walk or a vigorous jog?
What do we know already?
Your colon is your large intestine, sometimes also called your bowel. It's about two metres long, and carries food waste to your rectum, which then pushes the waste out of your body when you go to the toilet.
Colon cancer is one of the more common cancers. About 36,500 people are diagnosed with this cancer each year in the UK. More than 8 in 10 people diagnosed with cancer of the colon or rectum are aged 60 or over.
Previous studies have indicated that exercise cuts your chances of getting cancer of the colon. Doctors think this could be for a number of reasons.
- Exercise improves the way your body processes sugar in your blood, and means you don't need to produce so much insulin. This may help your digestive system work better.
- Exercise may reduce the amount of inflammation in your body.
- You're less likely to get constipation if you do plenty of exercise. So food waste moves faster through your colon.
- People who get out and about doing physical exercise may have more vitamin D, from being in sunlight. Vitamin D may protect against cancer.
The latest study looked at all the research that's been published on exercise and colon cancer, and summed up the results to give an estimate of how much protection exercise can give you.
What does the new study say?
Overall, the most active people in the published studies had a 24 percent smaller chance of getting colon cancer, compared to the least active people. The results were about the same for men and women.
Tell me more about the study's findings
Unfortunately, the new study can't tell us exactly how much exercise you need to do in order to cut your risk of colon cancer by 24 percent. That's because the individual studies used lots of different methods to measure exercise. Some studies say you need to do intense exercise such as jogging or swimming, while others say that walking is sufficient.
What we can say is that it doesn't seem to matter whether you're taking 'leisure' exercise, such as doing an aerobics class, or 'occupational' exercise such as working on a building site. The effects are similar.
How reliable are the findings?
It's probably true that taking exercise reduces the chances of getting colon cancer. The study looked at 52 previously published studies to summarise their results. But the new study doesn't make clear whether the researchers took into account other things that can affect your risk of colon cancer.
For example, being overweight and eating a lot of processed meat (such as bacon or sausage) both increase your risk of colon cancer. People who take lots of exercise are also likely to be a healthy weight, and eat a healthy diet. It's hard to tell whether exercise alone makes the difference. The individual studies may have adjusted their figures to account for this, but we can't tell without checking all 52 studies.
Where does the study come from?
The study was carried out by researchers from Washington University and Harvard University in the US. It was published in the British Journal of Cancer, which is owned by Cancer Research UK. The study was funded by the universities.
What does this mean for me?
There are lots of good reasons to do plenty of exercise. We know it's good for your heart, good for your mental health, and helps you avoid diabetes and dementia. If you need another reason, this study shows that keeping active probably also cuts your risk of a very common cancer.
What should I do now?
If you want to reduce your chances of getting colon cancer, you can:
- Eat a healthy, balanced, diet, restricting the amount of red and processed meat you eat
- Exercise regularly. Cancer Research UK recommends 30 minutes of exercise that makes you slightly sweaty, five days a week.
- Keep to a healthy weight.
- Drink alcohol in moderation and don't smoke
- Take part in bowel cancer screening when invited to do so.
Some people are at higher risk of colon cancer because of their genes, or because they have a disease like Crohn's disease or ulcerative colitis. People with certain inherited colon conditions need regular testing for colon cancer from an earlier age.
From:
Wolin KY, Yan Y, Colditz GA. Physical activity and colon cancer prevention: a meta-analysis. British Journal of Cancer. Published online 12 February 2009.
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