Colon cancer: who is at risk, and how can it be prevented?


By Noy Birger and Brandel France de Bravo, MPH
Updated 2016

When cancer begins in the colon (large intestine) or rectum, it is called colorectal cancer or colon cancer.

In the early stages, this cancer begins with small polyps, which are shaped like little mushrooms growing on the wall of the colon. Polyps are very common, especially as people get older. Not all polyps develop into cancer but all colorectal cancer begins with polyps. Certain kinds of polyps are more likely to lead to cancer than others, but the doctor can’t tell if a polyp is precancerous just by looking at it. This is why doctors prefer to remove and analyze any polyp found during screening. Polyps can be identified and removed by colonoscopy, in which a small camera on a flexible tube is inserted into the rectum.1

Thanks to more screening, the number of people diagnosed with colon cancer has decreased, but it is still the 4th most common cancer for both men and women.23The death rate is high because many people who are at risk for colon cancer do not get screened for the disease.4

A study published in February 2012 in New England Journal of Medicine found that patients who received colonoscopies and had noncancerous or pre-cancerous growths (polyps) removed, were half as likely to die from colon cancer than people in the general population who were not screened or used less effective screening methods. 5

Men and women are equally likely to die from colon cancer,6 but men are more likely to be diagnosed with colon cancer than women of the same age. 7 Black men and black women are at higher risk for developing colon cancer and dying from it than are white men and white women of the same age.89Being overweight or obese increases men’s risk of colon cancer more than it does women’s (see Obesity and Cancer: What You Should Know).  In the U.S., nearly one in ten cases of colon cancer is estimated to be caused by excess body fat.10

Risk factors for developing colon cancer

In addition to your sex and race, your age and genes are important risk factors you can’t do anything about. Your chances of developing colon cancer increase as you get older: 90% of cases are in people over 50. Having a family member with colon cancer also increases your chances of developing it. About 20% of people with colon cancer have a first-degree relative (parents, siblings or children) or second-degree relative (aunts, uncles, grandparents, grandchildren, nieces, nephews, or half-siblings) who also had colon cancer. 11

In addition to people with pre-cancerous polyps, people who suffer from ulcerative colitis or Crohn’s disease are more likely to develop colon cancer.12Ulcerative colitis and Crohn’s disease cause inflammation of the colon, which is why they are both also referred to as Inflammatory Bowel Disease (IBD). Chronic inflammations in the body seem to increase the risk of various types of cancer.

Less is known about what you can do to prevent colon cancer. People who eat too much fat in their diet or too little fiber or too little calcium, smoke, drink alcohol, don’t exercise enough, or are overweight are more likely to be diagnosed with colon cancer. However, scientists do not know whether people can lower their risks of getting colon cancer if they change one or more of those behaviors.  For example, several large research studies show that eating a high-fiber diet does not decrease your chances of getting colon cancer.131415On the other hand, there is clear evidence that fiber, calcium, exercising, maintaining a healthy weight, and avoiding smoking and alcohol is generally good for your health, whether it reduces your chances of colorectal cancer or not.

So, what can you do to lower your risk?

  • Get screened regularly from age 50 to 75. If you have a relative with colon cancer, your doctor may want to screen you earlier than age 50. The recommended screening tests are:
    • High Sensitivity Fecal Occult Blood Test (FOBT), which involves providing stool samples and should be done once every year
    • Colonoscopy (mentioned above), which requires anesthesia and is more expensive, and the doctor can remove polyps if found. It is only needed every 10 years unless a close relative developed colon cancer; and
    • Flexible sigmoidoscopy is similar to a colonscopy. It can be used to find polyps but not to remove them. It is recommended every 5 years

A “virtual colonoscopy,” which is done with a Computed Tomography (CT) scan, is more expensive than the other screening tools and is not recommended by the U.S. Preventive Services Task Force. As with any CT scan, it exposes you to relatively high levels of radiation (see Everything You Ever Wanted to Know about Radiation and cancer, But Were Afraid to Ask).

The advantage to a regular colonoscopy (not a virtual one) over the other methods is that polyps can be removed during the screening process. The disadvantage is that you need to take a day off from work, fast for about 12 hours and purge with large quantities of an unpleasant laxative drink. The advantage of the FOBT is that it is easier and less expensive. However, the FOBT and CT scan only detect potential problems or polyps – you would still need the colonscopy to have them removed if the results are abnormal. 16

  • Quit smoking. Cigarette smoking doubles your chances of getting polyps and long-term smoking increases the risk of colon cancer. It also increases your chances of dying from colon cancer.171819
  • Maintain a healthy weight. Extra pounds mean extra risk for all kinds of cancer, including colorectal cancer. Fat cells appear to trigger chronic inflammation of the body, which stresses the immune system.20
  • Eat a balanced diet. Be sure to include plenty of fruits and vegetables (especially ones from the cabbage family, like broccoli, cauliflower, cabbage, Brussels sprouts, and collard greens), limit the amount of red meat you eat (particularly well-done) and stay active. At least some of the research supports this kind of diet, and since eating this way offers so many different health benefits, why not try it? 2122
  • Get more Vitamin D through sunlight and supplements, since few foods are naturally rich in Vitamin D. Recent studies of doses higher than the 400 IU/day that is in standard multiple vitamins, show that Vitamin D can reduce the risk of colon cancer.23Blacks, who are at the highest risk for colon cancer, and people living in the northern half of the U.S., typically have too little Vitamin D in their bodies because they are exposed to less sun, and darker skin benefits less from sunshine.  And since Vitamin D is good for your health in many ways (see http://ods.od.nih.gov/factsheets/vitamind.asp),24 it makes sense to give this a try if you are concerned about colon cancer. Vitamin D is in milk and fortified breakfast cereals and in fatty fish such as tuna, salmon, and sardines, or you might consider a Vitamin D supplement.  Experts agree that adults can take up to 4,000 IU/day of Vitamin D without harming their health, and they recommend getting 5-30 minutes of sun at least twice a week. This means sun exposure to your face, arms or legs (preferably all three) without sun screen and between 10:00 a.m. to 3:00 p.m. However, too much Vitamin D can be dangerous.  The best way to make sure you are getting enough Vitamin D, but not too much, is to get your Vitamin D levels checked the next time you visit your doctor.
  • Low-dose aspirin. The U.S. Preventive Services Task Force found that taking low-dose aspirin can help prevent colorectal cancer and heart disease in some adults, depending on age and other factors. For more information, see: Aspirin Use for the Primary Prevention of Cardiovascular Disease and Colorectal Cancer: Consumer Guide. [PDF-212K]. Despite some early studies, there is no clear evidence that other types of anti-inflammatory products help prevent colorectal cancer, such as ibuprofen or fish oil tablets.

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