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

By Noy Birger and Brandel France de Bravo, MPH


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,2 The death rate is high because many people who are at risk for colon cancer do not get screened for the disease.3

A study published in the February 2012 issue of the 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. 4

Men and women are equally likely to die from colon cancer,5 but men are more likely to be diagnosed with colon cancer than women of the same age. 6 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.78Being 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.9

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 the older you are: 90% of cases are in people over 50. Another major risk is having a family member with colon cancer. 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. 10

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.11Ulcerative 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. 121314

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. There are several ways to get screened
  • The Fecal Occult Blood Test (FOBT), which involves providing stool samples and must be done once every year
  • Colonoscopy (mentioned above), which requires anesthesia and is more expensive, but can be done much less frequently; and
  • “Virtual colonoscopy,” which is done with a Computed Tomography (CT) scan. This is more expensive and because it is a newer technique, not all insurance policies cover it. 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, fasting for about 12 hours and purging 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. 15

  • 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.161718
  • 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. 19
  • Consider taking Omega-3 fatty acid supplements, such as fish oil capsules, since they combat inflammation.  Properties in oily fish (EPA andDHA) reduce tumor growth and help the body destroy cancerous cells. In animal studies, Omega-3 fatty acids were found to reduce new cases of colon cancer, but we don’t yet know if this will work in humans.  However, fish oil supplements have other advantages, so it’s a reasonable strategy.  Ground flax seed, which can be added to cereal, salads, and other foods, is also very high in Omega-3.20
  • 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.232425Blacks, 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,26 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 between10:00 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.
  • High doses of aspirin and other NSAIDs (non-steroidal anti-inflammatory medicines), such as ibuprofen and naproxen, (more than 300 mg per day), can reduce the chances of developing colon cancer, but such high doses can cause bleeding, ulcers and other problems.  For that reason, the risks outweigh the benefits for most people.27


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