Can exercise reduce the risk of breast or bowel cancer?

There is good evidence from research that physical activity can help to prevent breast cancer, bowel cancer and womb cancer. 

For breast cancer, studies have shown a protective effect ranging from 20 to 40%. So being active may lower your risk by between a fifth and just over a third. The researchers think that this protective effect comes from a lowering of levels of hormones and growth factors.

There have been over 50 studies looking at exercise and preventing bowel cancer. The largest studies show that exercise could reduce bowel cancer risk by about a quarter (25%). By maintaining a healthy weight as well, the studies estimate that bowel cancer risk could be as much as halved, compared to people who are overweight and don't exercise.

Womb cancer risk is also lowered by exercise, by between a fifth to a third (20 to 30%).

There is a little evidence that exercise may help lower risk of other cancers, for example prostate cancer.  But the evidence is not so strong as it is for bowel, breast and womb cancer.  But for most other cancer types we don't have evidence that exercise lowers your risk. 

It isn't completely clear how exercise helps. It may be by helping keep your weight down. Being overweight increases a woman's risk of hormone related cancers. This means breast and endometrial cancer (cancer of the lining of the womb). Obese men may have an increased risk of bowel, rectal or prostate cancers. Obese means more than about 25% overweight. It is measured by comparing your weight with your height, known as your body mass index.

We know that exercise affects some of the chemical balances of the body. It can lower insulin levels and the levels of some other hormones and growth factors. In bowel cancer, exercise can also lower bowel inflammation and help to stop constipation. So potential cancer causing substances are in the bowel for a shorter time.

There is more information about the evidence for exercise reducing cancer risk in the Healthy Living section of our News and Resources website.

Exercise is also well known for helping to reduce stress. Doctors don't know how important stress is in cancer. Reducing your stress can certainly help you to smoke less or drink less alcohol. Some doctors think that stress damages the immune system. In theory at least, a damaged immune system  could help a cancer to start or grow more quickly. Taking regular exercise will certainly help you feel better and less stressed. Living more healthily will reduce your risk of many illnesses, for example heart disease and diabetes. And a healthy lifestyle may reduce your risk of getting some types of cancer as well.

You may find our page about exercise guidelines for cancer patients useful to read.