Fact Sheet: Bowel cancer prevention

What is bowel cancer?

Bowel cancer usually means cancer of the large bowel, which is the colon, the rectum and the anus (back passage). The medical term for cancer of the large bowel is colorectal cancer. Cancer of the small bowel is rare.

Bowel cancer usually starts in the mucus lining inside the bowel. As people get older, little lumps called polyps or adenomas will grow there. These are usually harmless. Only about 5 out of 100 of these polyps will ever become cancerous, and it takes about 5 to 10 years for this to happen. Polyps can be seen during a colonoscopy. This is why removing polyps could prevent bowel cancer developing.




What are the signs of bowel cancer?

There are no specific signs of bowel cancer. The first warning signs are similar to those of other more common problems like haemorrhoids (piles), ulcerative colitis or Crohn's disease. These signs are blood or mucus in the stools, or changes in bowel patterns that last for several weeks (diarrhoea or constipation). Although it is not likely to be cancer, seeing a doctor about these problems could mean catching a cancer early if one does develop.

How big is the risk of getting bowel cancer?

In developed countries, about 1 out of 18 people will get bowel cancer at some time in their lives, but the risk is very small for younger people. The risk of bowel cancer grows with age. The risk also increases if close family members like parents and brothers or sisters have had it.

People are at particularly high risk of bowel cancer if they have inherited one of two conditions: hereditary non-polyposis colorectal cancer (HNPCC) or familial adenomatous polyposis (FAP). Polyposis simply means a large number of polyps. People who have FAP could get more than 100 polyps. Having an inflammatory bowel disease for years also increases the risk of developing bowel cancer.

What are the possible ways to prevent bowel cancer?

There are several factors that people who have a lower risk of bowel cancer have in common. These include having diets high in fibre, fruit and vegetables and lower in processed and red meat. People who have regular daily exercise are also less likely to get bowel cancer. People who are overweight or obese have a slightly higher risk of getting bowel cancer. However it does not automatically follow that, for example, a change in diet or losing weight will reduce bowel cancer risk.

Research is needed before we can know for sure if a lifestyle change or other factor can prevent bowel cancer. These kinds of studies have been taking place for several years. The state of knowledge on bowel cancer prevention is summarised briefly here.

Fibre, fruit and vegetables: Researchers have tested whether or not the risk of bowel cancer is reduced if people increase the fibre in their diet, for example, by taking fibre supplements, or eating more fruit and vegetables. These studies did not show that this can protect against bowel cancer. More studies are under way.

Antioxidant vitamin supplements and minerals: Research on the antioxidants such as vitamin C, vitamin E and beta-carotene show reason for caution. These vitamins, alone or in combinations, have not been shown to prevent bowel cancer. If anything, people who took these vitamins actually died slightly more often. This difference was very small, but it was enough to help rule out antioxidants as a way of preventing bowel cancer. There has also been no success with folic acid or folate supplementation. It is too soon to know whether or not selenium supplements are effective.

Calcium : Studies have shown that people who take relatively large calcium supplements developed fewer polyps. This supports the theory of a preventive effect. However, researchers remain cautious, because something that slows down the growth of polyps does not necessarily also prevent bowel cancer, which develops far more slowly.

Drugs: Various drugs are being studied to see if they can prevent bowel cancer, but no drug has yet been licensed as effective for this purpose. The drugs being tested include acetylsalicylic acid (ASA) and other similar so-called non-steroidal anti-inflammatory drugs or painkillers. Daily use of these drugs might slow down the growth of polyps. However these drugs can have many adverse effects especially when taken over the long term, so these adverse effects and the potential benefits must be carefully weighed. More research is needed on this option. Statins (cholesterol-lowering drugs) do not seem to prevent bowel cancer.

Menopausal hormone therapy can slightly reduce the risk of bowel cancer, but it also slightly increases the risk of breast cancer and stroke. Having taken the oral contraceptive pill for several years might reduce a woman's risk of bowel cancer. Because of this, new types of hormonal and other drugs are being developed to try to find more ways to prevent bowel cancer.

© IQWiG (Institute for Quality and Efficiency in Health Care)