Can exercise really reduce the risk of getting cancer?

Just in case you haven’t got the message that exercise is good for you, two huge research studies this week shout it louder than ever. Which is just as well, since almost one-third of adults are classified as “inactive”. Exercise is already known to reduce the risk of breast, colon and endometrial cancer (cancer of the lining of the uterus) by between 10% and 40%. Now, a pooled analysis of data from studies looking at 1.4 million adults between the ages of 19 and 98 has found that exercise reduces the risk of an additional 10 cancers, including oesophageal, stomach, bladder and kidney. What’s more, for many cancers, exercise reduces the risk even in overweight people. This is particularly interesting, because the mechanism by which exercise is thought to protect from cancer is weight reduction.

It seems that exercise may work its magic in a variety of ways. Dr Marilie Gammon, an epidemiologist from the Gillings School of Global Public Health in Chapel Hill, North Carolina, who wrote an editorial to accompany the paper in the peer-reviewed journal JAMA Internal Medicine, says that exercise may help to repair DNA when it is damaged by cancer-promoting substances. Exercise may also alter hormone levels and reduce inflammation.

The study showed that the risk of oesophageal cancer for those taking the most exercise was 42% lower than for those taking the least. For seven of the cancers, the risk reduction was one-fifth or more. Gammon says the data was based on four hours of activity a week – the standard recommendation to prevent heart disease.

How active you have to be to reduce your cancer risk is unknown. Gammon suggests anything is likely to be beneficial – even taking the stairs instead of the lift.

But why stop at exercise? The second study of lifestyle and cancer, which took data from 136,000 Americans, found that anyone who quits smoking; does two and a half hours of moderate exercise a week; has no more than one drink a day if a woman or two if a man; and keeps to a BMI between 18.5 and 27.5 is likely to reduce their risk of bowel cancer by 30% and breast cancer by 12%.

Get on your bike

So, are you doing enough to reduce your risk of getting cancer? While these studies can’t prove that exercise reduces the risk of cancer – because they only report an observed association – they show a strong link, which is enough for me to get out my bike tomorrow. The fact that you can be overweight and still see a reduction in risk means you can get the benefit whatever your size. Dr Stephen Moore, the author of the JAMA Internal Medicine paper, is reported to run every day. Get moving.

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