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There are many things that can make you more or less likely to get colon or rectal cancer.

If you have a close relative who has had colon or rectal cancer, your chances of getting the disease are increased.

If no one in your close family has had colon or rectal cancer, your chances of getting this type of cancer are 2 in 100 .¹ This means that 1 in 50 Americans who have no relatives with colon or rectal cancer will get the disease.

But if one of your parents, a brother, a sister or a child has had colon or rectal cancer, your risk increases to about 1 in 17. The more relatives you have with the disease, the bigger your risk becomes.¹ And if you have a close relative who was younger than 45 when diagnosed with colon or rectal cancer, your risk moves to 1 in 10.

Some inherited conditions can lead to colon and rectal cancer. (When a condition is inherited, this means that it can be passed on from parent to child.) Two particularly important ones are familial adenomatous polyposis (FAP for short) and hereditary nonpolyposis colorectal cancer (HNPCC for short). See Inherited conditions that can lead to colon and rectal cancer.

Your chances of getting colon or rectal cancer increase as you get older, especially after you've reached age 50. About 9 in 10 people who have colon or rectal cancer are over 50.²

Scientists have found that colon and rectal cancer is more common in the United States and other developed countries than in undeveloped countries. They think the reason may be a high-calorie diet, especially one that's rich in meat, fat and oil.³ The type of fat seems to be important. A diet rich in animal fat and red meat (but not vegetable fat) seems to increase the risk of colon and rectal cancer. However, fish oils may protect you from this cancer.^{4 5}

The role of fiber in the development of colon and rectal cancer is less clear. Scientists used to think that eating fiber protected you from this disease. They thought it helped move waste (feces) through the colon and rectum more quickly. This meant that possibly harmful materials in the feces were in contact with intestine wall for less time. But this theory has been dropped. Eating more fiber has not been shown to speed up the passage of feces.³

If you have an inflammatory disease of your bowels, you're more likely to get colon or rectal cancer. These diseases include ulcerative colitis and Crohn's disease. Also, the longer you have one of these diseases, the greater your risk of getting colon or rectal cancer. Research shows that up to a third of people who've had one of these diseases for more than 25 years will get colon or rectal cancer.³ The reason for this is unclear.

Smoking can increase your risk, especially if you've smoked for more than 35 years. No one knows how smoking makes you more likely to get this cancer.³

Drinking alcohol every day can increase your risk of getting colon or rectal cancer, but no one knows why. You may also be more at risk if you're overweight, especially if you carry your extra weight around your middle. However, regular exercise and eating less may protect you against this cancer.^{4 5}

Some women take hormone replacement therapy (or HRT for short) during menopause to help their hot flashes and other symptoms. HRT may also reduce your risk of colon and rectal cancer, although this lowered risk disappears five years after you stop the treatment.^{4 5} However, HRT also increases the risk of getting some conditions, including breast cancer and heart disease. To learn more about these risks, see HRT in our section on menopause.

Taking the pills also seems to offer some protection against colon and rectal cancer.^{4 5}

There is some evidence that aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) might protect you from colon and rectal cancer.^{4 5} However, some of these drugs have been linked with serious side effects. If you take an NSAID for a long time, it may slightly increase your risk of a heart attack or a stroke. This risk doesn't apply for aspirin. To learn more see, Warnings about side effects of NSAIDs.

NSAIDs and aspirin can also cause stomach ulcers if taken for a long time. For these reasons, doctors do not yet recommend taking aspirin or other NSAIDs to prevent colon and rectal cancer.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.