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Protect Yourself Against Colon Cancer
Colon cancer, more accurately called colorectal cancer, includes cancers of the rectum and colon. It usually begins with polyps, small benign growths in the inner wall of the colon or rectum. Some polyps (especially those known as adenomas) become malignant for reasons that are largely unknown. Age is a risk factor: most people who get colon cancer are over 50. Environmental factors—particularly smoking—also play a role. Ulcerative colitis or any other chronic inflammatory bowel disease puts you at higher risk. Family history of colon cancer is a risk factor, too.
But not all the old hunches have proved out. Dietary fiber, for instance, may not play a protective role. And red meat may not be as clear a risk as once was thought.
The good news: It is possible to detect polyps before they become cancerous, or at an early stage before the cancer has spread. By far the most important way to prevent colon cancer is to get screened. The next most important step is not to smoke.
As for other things that may reduce the risk of colon cancer, here’s the latest thinking:
What you eat
• A diet rich in fruits, whole grains, and vegetables appears to lower the risk of many cancers, including colon cancer. Vegetables most likely to help prevent colon cancer are broccoli, cabbage, cauliflower, kale, and other members of the cruciferous family.
• Fiber, however, is no longer deemed important in preventing colon cancer. True, a high-fiber diet helps prevent constipation, and the theory was that this might reduce exposure of the intestinal wall to carcinogens. But several large studies have failed to find a protective effect for fiber. And there’s no known link between constipation and colon cancer. The Women’s Health Initiative (one of the largest recent studies) did not find that a high fiber intake reduced colon cancer risk. Still, another large study did find that a very high intake of fiber was protective. Fiber is hard to study—it isn’t just one compound but many.
• A high-fat diet, particularly one high in animal fats and red meats, has been blamed for increasing colon cancer risk, but the jury is still out. Dietary fat, in itself, is no longer regarded as a factor in colon cancer. If red meats do increase the risk—and some evidence suggests they do—it may be because they are often cooked at high temperatures, so that potential cancer-promoting chemicals are formed. In any event, there are other reasons, such as heart health, to avoid a diet high in animal fats.
• may reduce the risk of colon cancer, whether you get them from food or supplements. A Harvard study in 2002, for instance, found that consuming at least 700 milligrams of dietary calcium daily was associated with a reduced risk of certain types of colon cancer. A review article last year in Nutrition Research Reviews found that a high intake of dairy products, especially milk, was also associated with a reduced risk of colon cancer, perhaps because of their calcium, vitamin D, and other nutrients.
• Omega-3 fats from fish may reduce the risk of colon cancer, though the evidence is preliminary.
• Folate, a B vitamin, may also reduce the risk of colon cancer. A diet rich in fruits and vegetables may be beneficial, in part, because these foods tend to be high in folate. But not all research has supported this idea, and as we reported in September, in people prone to precancerous polyps, high doses (1,000 micrograms daily of folic acid, the form of folate used in supplements) encouraged polyp growth. This was surprising, since the supplement was expected to reduce recurrence. Thus, we advise people (except women of childbearing age) to limit their intake of folic acid from supplements and fortified food to not much more than 400 micrograms a day (the Daily Value). You don’t need to worry about folate that occurs naturally in foods, which has never been shown to promote cancer.
What to do
• Don’t smoke. Tobacco is a known risk factor for colon cancer.
• If you drink, keep your intake moderate—no more than two drinks a day for men, one for women. There may be a link between high alcohol intake and colon cancer.
• Exercise regularly, and lose weight if you’re overweight. Even in moderate amounts, exercise appears to be protective.
• Get screened. See below.
Tests to take for colon cancer
Everybody over 50 should be screened at regular intervals, with those at higher risk—such as blacks and people with a family history—starting earlier. This can save your life, since the tests can detect polyps while they are still benign, or can detect cancer at an early, curable stage. Talk with your doctor about screening. By far the best test is colonoscopy, but any test is better than none. The tests include:
• Digital rectal exam. Part of a routine physical exam, this is quick and easy. But it can find only tumors within reach, so it is not enough.
• Fecal occult blood test (FOBT) detects hidden (“occult”) blood in a stool sample. The doctor gives you a kit to take home; you then send a smear to a lab. If blood shows up, it may have come from something besides cancer—that is, the result may be a false-positive. FOBT may also miss cancers. You’ll be referred for further testing if blood is detected. A newer version, the immunological fecal occult blood test, has a reduced risk of false-positives. Another option
is the flushable reagent pad, available without a prescription and requiring no lab test. You must do FOBT every year.
• Flexible sigmoidoscopy. Done by many primary-care doctors, this exam of the lower half of the colon with a flexible lighted tube is accurate and safe. Small polyps can be removed and biopsied if necessary. If anything suspicious is found, you’ll need a colonoscopy to check the upper colon. To prepare, you need an enema the day of the exam. The test should be done every five years. And you will also need an annual FOBT—see above.
• X-ray with barium enema requires fasting and strong laxatives. A chalky solution is pumped into the rectum, followed by air to expand the colon, which is then X-rayed. This test should be repeated every five years. It may miss small polyps. If an abnormality is seen, you will need a colonoscopy.
• Colonoscopy is an examination of the entire colon via a flexible scope monitored on a video screen. If polyps are found, they can be removed right then for further testing. This test requires a specialist, as well as someone to administer sedation and assist with recovery. Expensive but highly accurate and valuable, it requires a clear-liquid diet and strong laxatives the day before. Testing every 10 years is sufficient if no polyps are found. Otherwise, your physician may recommend retesting in three to five years. If you have a colonoscopy, you need no other tests.
• Virtual colonoscopy is similar to conventional colonoscopy, except that the colon is visualized by a CT scan after the colon is inflated with air. No sedation is needed, and the test is less invasive than a regular colonoscopy. As with the regular exam, you have to go on a clear-liquid diet and take a laxative the day before. Recent studies have shown this method to be promising—but if polyps are found, a regular colonoscopy will have to be done. Like any CT scan, it exposes you to some radiation.
UC Berkeley Wellness Letter, December 2009
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