About one mil-lion people worldwide are diagnosed to have colon cancer every year, according to the World Health Organization. In the Philippines, it is the third most common cancer in men and women.
As with many of the most common cancers, some colon cancer is clearly caused by inherited genetic mutations that are passed from generation to generation. But that’s a relatively rare event. Fewer than five percent of cases are caused by the two main genetic disorders that have been identified so far: familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer.
Another 25 percent of patients fall into a gray area. In this form, the disease runs in families, so there seems to be some inherited genetic component, but the pattern of who is affected and who isn’t suggests other causative factors as well. About 70 percent of colon cancers cannot be explained by family history or an obvious inherited factor. Doctors sometimes refer to these as “sporadic” cases although they are the most common. In most instances, therefore, colon cancer has more to do with what we eat, how much we exercise, how much we weigh, and a number of other factors.
There are no guarantees, of course, but most of us can lower our chances of getting colon cancer in several ways: Don’t eat too much red meat, don’t get heavy, exercise, and, for heaven’s sake, don’t smoke.
Starting at about age 50, regular screening — colonoscopy is increasingly favored — improves the chances of avoiding colon cancer and also of surviving it even if you do get it. Screening works because colon cancer is usually a slow-growing disease that starts with adenomatous polyps, small protuberant growths inside the colon that may contain precancerous cells. Screening tests are designed to find these polyps so doctors can remove them before they become cancerous.
But the truth of the matter is that most of us tend to put off screening tests, perhaps especially so for colon cancer. As for other admonitions, cutting back on red meat may not be so difficult. But the gap between word and deed looms especially large when it comes to weight control and exercise. So we do need easier, more reliable ways of preventing colon cancer.
Aspirin Is Too Risky
The daily, low-dose (81- to 325-mg) aspirin is one possibility. Many people already take aspirin to reduce their risk of having a second heart attack or stroke — or having their first one if they fall into a high-risk group (a not-very-exclusive club that includes many men over 40 and postmenopausal women). Aspirin also seems to have anti-cancer properties. In lab and animal experiments, it has prevented the rapid cell division that’s associated with cancer. And epidemiologic studies show that people who take aspirin are about half as likely to get colon cancer as those who don’t, although the protective effect seems to emerge only after 10 years or more of regular intake.
Early last year, the US Preventive Services task force recommended against taking aspirin — or any other nonsteroidal anti-inflammatory drug — for colon cancer prevention, if your colon cancer risk is average. The well-known risks of these drugs (intestinal bleeding, kidney problems, and “bleeding” strokes) outweigh the possible colon cancer protection, the experts decided. Still, there’s room for exercising some judgment. If a person at high risk of colon cancer is at low risk for complications from aspirin — and would benefit from taking it for other reasons (presumably cardiovascular) — then it’s reasonable to at least consider aspirin for reducing colon risk.
Folic Acid Falters
Another contender for colon cancer prevention-in-a-pill has been folic acid, the synthetic form of folate, which is found naturally in green leafy vegetables and other foods. One of the B vitamins, folic acid looks pretty good as an anti-cancer agent. Evidence from animal studies hint at cancer protection from folic acid and epidemiologists have found a connection between low folic acid intake and colon cancer, particularly in people who drink alcohol. Yet, in a study published in the Journal of the American Medical Association (JAMA), the study volunteers who took folic acid pills were more, not less likely to get recurrent polyps than those who took a placebo pill.
So, does folic acid join the growing list of vitamins and minerals (vitamin A, vitamin E, and perhaps selenium) that go from being healthful to harmful when taken in large amounts in pill form? At the moment, no one knows for sure and the studies have been inconclusive. Some scientists speculate that perhaps the surplus folic acid overwhelms systems in the intestine that metabolize the vitamin. Others have theorized that folic acid in certain amounts may prevent colon cancers from forming but in large amounts may “feed” small microscopic cancers if they’re already there.
Tips On Lowering Your Risk
And so, the search for answers circles back to some familiar recommendations. Here’s the latest thinking on what helps and what doesn’t:
• Cut back on red and processed meat. The studies don’t line up perfectly but many point to increased colon cancer risk among people who eat a lot of red (beef, lamb, pork) and processed meat (bacon, ham, hot dogs, sausage, and so on). The risk from processed meat might be greater than it is for red meat. Why red meat might cause colon cancer is unclear. Some studies suggest that the heme iron it contains, promotes cell division and cancerous growth. Chicken doesn’t seem to increase colon cancer risk, and one study found it might even reduce the risk.
• Stay active. Whether it is on or off the job, physical activity seems to protect against colon cancer (but curiously, not against rectal cancer). Some studies suggest that you’ll get even more protection if you exercise vigorously. But Danish researchers reported in 2006 that activity level wasn’t as important as the number of different activities people participate in.
• Stay slender. Scientific studies have identified a connection between obesity and colon cancer more than 10 years ago. Being overweight increases your risk but only half as much as being obese. Visceral fat, which accumulates in the belly and clings to the abdominal organs, may pose more of a risk than fat under the skin that widens hips, thighs, and buttocks.
• Adequate calcium intake is good for most. High milk and calcium consumption have been linked to lower cancer risk in epidemiologic studies. But when daily calcium (1,000 mg) and vitamin D (400 IU) supplements were tested in the landmark Women’s Health Initiative Study, they had no effect on colon cancer rates. Other data suggest that we’ve paid too much attention to calcium and that vitamin D is the real risk reducer. Men are expressly advised by the American Cancer Society not to get too much calcium (1,500 mg or more daily) because large amounts may increase prostate cancer risk. The bottom line: People who have had polyps should talk with their doctors about taking calcium supplement (one important trial showed reduction in recurrence by 20 percent).
• Nothing special about fiber. Loading up on fiber was once thought to be our best defense against colon cancer. No more. In clinical trials, fiber hasn’t worked to reduce recurrent polyps, and the evidence that it protects against first-time polyps is uneven. (Diets high in fiber do seem to reduce the risk of heart disease and diabetes so don’t forget about it entirely.)
• Hormone therapy isn’t worth the other risks. If colon cancer were the only health concern, many women might consider taking hormones to prevent it. In the Women’s Health Initiative Study, postmenopausal women who took an estrogen-progesterone combination lowered their risk for colorectal cancer by 44 percent. But hormone therapy has other risks associated with it (including breast cancer and heart disease (depending on when it’s taken relative to menopause), so it’s not recommended for cancer prevention.
• Get screened. In developed countries, the number of people dying each year of colon cancer has been declining. Treatment has improved, so people with the disease are also living longer. Screening, so cancers are caught earlier, has played a major role in the reduction of mortality from colon cancer. This important topic will be discussed next week in this column. Don’t miss it. It may save your life.