Life Extension Magazine

Life Extension Magazine March 2005

Report

Nutritional Strategies for Conquering Colon Cancer

By Debra Fulghum Bruce, PhD

Fiber. Despite 30 years of study, data on the association between dietary fiber and colon cancer risk are still inconclusive. A much-publicized study by Harvard University scientists in 1999 found no correlation between dietary fiber intake and colorectal cancer risk.25 Other studies, however, suggest that dietary fiber may indeed reduce the risk of colon cancer.26 An American Cancer Society study examined the relationship between colon cancer and the consumption of whole grains, fruits, vegetables, and dietary fiber. They found that men with the highest vegetable intake experienced reduced risk, while men with the lowest intake of vegetables and dietary fiber were at greater risk.27 Since fiber-rich fruits and vegetables are known for their many other health-promoting benefits, it seems prudent to consume them in abundance while scientists continue to unravel dietary fiber’s association with colon cancer.

Selenium. An essential trace mineral, selenium is one of the most important cancer-preventive nutrients. Scientists have noted a statistically significant correlation between low soil concentrations of selenium and increased rates of colorectal cancer.28 Scientists believe that selenium-poor soils contribute to low dietary selenium intake by their influence on the nutritional quality of locally grown foods. In studies, selenium compounds have inhibited tumor formation in various animal models, and other research suggests that supplemental selenium may reduce cancer risk in humans.29 Selenium is incorporated in numerous proteins in the body, including glutathione peroxidase, a powerful antioxidant. These selenium-containing proteins appear to offer antioxidant protection from reactive oxygen species that can damage DNA and alter protein function.30

Patients prone to colon adenomas have demonstrated low selenium levels. Supplementation can normalize selenium levels and thus may reduce the incidence of colon cancer.30 Epidemiological studies suggest that selenium reduces the risk of certain cancers, including colon cancer.31

Omega-3 fatty acids. Fish oil contains the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Epidemiological studies and animal experiments suggest that both EPA and DHA exert protective effects against colon cancer.32 In patients with colon cancer, EPA and DHA decrease cell proliferation and favorably modulate the balance between colon cell proliferation and apoptosis.32 In a laboratory study of mice, University of Texas researchers found that omega-3 fatty acids block the action of a chemical called protein kinase C beta II, which is thought to promote colon cancer, suggesting a potential role for omega-3 fatty acids in preventing colon cancer.33

SCREENING TESTS FOR COLON CANCER

Flexible-tube colonoscopy is the most invasive and accurate of colon cancer screening tests. It requires laxative-induced preparation of the colon the day before the procedure and may require sedation during it. The cost ranges from roughly $600 to $2,000. Medicare and some health insurance plans now pay for this procedure. Depending on family history of the disease and whether polyps are discovered, the test should be repeated every three to five years. The American College of Gastroenterology now considers this form of colonoscopy to be the “preferred” screening test.43

Sigmoidoscopy requires no sedation, but examines only the lower third of the colon, where most cancers occur. Polyps are biopsied, and adenomatous or cancerous polyps are removed by sigmoidoscopy or flexible-tube colonoscopy. The cost is a few hundred dollars, and the test is repeated every five years. The risk of missing cancer in the upper two thirds of the colon makes sigmoidoscopy only partially effective and therefore not highly recommended.

Barium enema requires no sedation, but if polyps are found, a flexible-tube colonoscopy is necessary for treatment. The cost is a few hundred dollars, and the test should be repeated every five years. This procedure exposes the lower abdominal cavity to radiation that may be associated with increased risk of cancers, and thus is not recommended.

Fecal occult blood test is a routine test conducted in a physician’s office that looks for blood in the stool. The cost is around $25 and the test is repeated annually. This test can be negative in those with colon cancer, as not all polyps bleed all the time.

Virtual colonoscopy is a 15-minute, computer-enhanced screening test (also called CT colonography) that does not require sedation and uses a computerized technology scanner to provide three-dimensional images of the entire colon. The cost ranges from about $1,000 to $2,000, and a flexible-tube colonoscopy is required to remove any polyps found. High-dose radiation exposure, the inability to remove polyps found, and a lower detection rate of polyps and cancerous lesions makes virtual colonoscopy less desirable than flexible-tube colonoscopy.

Functional Foods

A considerable body of literature suggests that specific compounds in tea, red wine, and turmeric (curcumin) inhibit the COX enzymes, thus reducing prostaglandin-mediated effects on the colon. Because colon tumors have been shown to strongly express the COX-2 protein, and many cancer-preventive NSAIDs suppress the COX enzymes, it is tempting to speculate that these functional food compounds may help to prevent colon cancer by inhibiting one or both forms of the COX enzyme.

Green tea. Green tea is rich in polyphenolic compounds, with catechins as its major component. Studies have shown that catechins possess diverse pharmacological properties that include antioxidant, anti-inflammatory, anticarcinogenic, anti-arteriosclerotic, and antibacterial effects. In the gastrointestinal tract, green tea has been shown to activate intracellular antioxidants, inhibit pro-carcinogen formation, and suppress angiogenesis and cancer cell proliferation.34

THE SCIENCE BEHIND
“AN APPLE A DAY”

Quercetin, a compound found in fruits and vegetables, may be a primary reason why the adage “an apple a day keeps the doctor away” has endured. Quercetin is a major dietary flavonoid present in high concentrations in apples, onions, tea, and other foods. German researchers recently discovered that a high dietary intake of plant foods helps prevent colorectal cancer in humans, and that flavonoids, as part of such a diet, are considered to contribute to those protective effects.

Quercetin alters the levels of various proteins involved in the growth, differentiation, and apoptosis (destruction) of colon cancer cells. These cells have been iden-tified as molecular targets of quercetin, helping to explain the anti-cancer effects of this flavonoid.44

The most prominent catechin in green tea is epigallocatechin-3 gallate (EGCG), which modulates numerous molecular targets in the presence of inflammation and cancer.35 In-vitro cell culture studies show that tea polyphenols potently induce apoptotic cell death and cell cycle arrest in tumor cells but not in their normal cell counterparts.36 Animal studies have revealed that green tea inhibits tumor incidence and multiplicity in the colon and other organ sites.36

A large, population-based, case-controlled study in China found that consuming green tea reduced the risk of cancers of the colon, rectum, and pancreas.37 Tea polyphenols have been found to influence the metabolism of arachidonic acid in human colon mucosa cells and colon tumors by inhibiting the lipoxygenase and cylooxygenase enzymes. This mechanism may be responsible for some of green tea’s protective effects against colon cancer.38

Resveratrol. A red wine poly-phenol, resveratrol is considered cancer chemopreventive because of its antioxidant and antimutagenic effects.12 Inflammatory bowel disease in humans is known to be a major risk factor for colon cancer. In an animal study, resveratrol reduced the tissue injury caused by experimentally induced colitis, and also alleviated oxidative damage.39 These promising results suggest a role for resveratrol in modulating colon cancer risk, particularly for those at heightened risk because of inflammatory bowel disease.

Curcumin. Extensive research during the past 50 years indicates that curcumin (diferuloylmethan), the yellow pigment in the curry spice turmeric, can prevent and treat cancer. The lower incidences of colon cancer in Asian nations have been attributed to their intake of curcumin, which has been widely used for centuries without toxic effects. This phytonutrient inhibits some COX-2 while also inhibiting the actions of lipooxygenase, another enzyme involved in inflammation. Curcumin also inhibits the promotion and progression stages of carcinogenesis in cell cultures and animal studies.13

Scientists have theorized that cancer incidence at different body sites may be related to oxidative damage, which may in turn be modified by plant phytochemicals. When scientists from India’s National Institute of Nutrition studied curcumin’s protective effect against DNA damage in human cells, they concluded that this non-nutritive dietary constituent possesses antimutagenic properties and appears to be a promising chemopreventive agent.40

In the past year, researchers at the MD Anderson Cancer Center in Houston, TX, have revealed how various synthetic NSAIDs such as aspirin and ibuprofen, as well as natural compounds such as curcumin and resveratrol, that inhibit tumor cell proliferation. Recently published in the journal Oncogene, the study concluded that resveratrol and curcumin were among the most potent anti-inflammatory and antiproliferative agents, while aspirin and ibuprofen were (surprisingly) among the least potent.41

Conclusion

The prevalence of colon cancer is frighteningly high, and the disease will kill some 57,000 Americans this year. You can begin a program of colon cancer prevention today by heeding the myriad studies that endorse the importance of a healthy diet and lifestyle, dietary supplementation, and preventive screening.42 The good news is that colon cancer’s lethality could be greatly reduced with widespread and regular screening by colonoscopy. A colonoscopy allows for the removal of precancerous polyps before they develop into cancerous lesions. If an early-stage cancerous lesion is detected, the chance of curing it is very good. If one waits for physical symptoms of colon cancer to manifest, however, the mortality risk is terribly high.

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