A common yet preventable disease, colon cancer is the second leading cause of cancer death in both sexes, accounting for about 10% of all cancer deaths. Colon cancer is the third most common cancer in both men and women, and is also the most hereditary of all cancers: about 10% of adults with colon cancer have a family history of the disease.1 Although colon cancer is rarely diagnosed in people under the age of 40, its incidence increases significantly between the ages of 40 and 50, and its age-specific incidence rates rise in each decade of life thereafter.2
While today’s diagnostic and therapeutic tools are highly advanced, abundant research suggests that certain nutrients may help people avert colon cancer altogether.
Although colon cancer usually strikes after age 40, the disease process begins silently and without warning much earlier in life. Several environmental and genetic factors influence one’s susceptibility to colon cancer. According to the American Cancer Society, most colon cancers begin as a polyp (adenoma) or growth on the inside of the rectum and colon. Removing these adenomas early may prevent them from becoming cancerous. Other key risk factors for colon cancer include having an inflammatory bowel disease (Crohn’s disease or ulcerative colitis) or diabetes, or having a family member with colon cancer. Unhealthy lifestyle factors, such as lack of exercise and obesity, also raise one’s risk for colon cancer, as does the typically Western diet rich in red and processed meats, sweets, and refined carbohydrates.3
The early stages of colon cancer may be marked by symptoms such as abdominal pain, a change in bowel habit, or fatigue and weakness. Anemia and weight loss in the absence of gastrointestinal symptoms can signal colon cancer.4 Yet many people with colon cancer have no signs or symptoms of the disease at all.
As with many serious diseases, colon cancer is treatable if detected early, and today’s advanced screening exams and imaging techniques allow doctors to make well-informed treatment decisions. Many experts believe that death from colon cancer could be prevented if men and women at average risk for the disease begin screening tests at the age of 50. For people at greater risk due to family history or inflammatory bowel disease, screening should be started earlier.5 (The Life Extension Foundation recommends flexible-tube colonoscopy screening to detect early-stage colon cancer beginning at age 40. See “The Colonoscopy Dilemma,” Life Extension, December 2004.)
New Discoveries, New Targets
In the late 1970s, Dr. William R. Waddell noticed that when he gave sulindac, a drug similar to aspirin, to patients with an inherited disorder that leads to hundreds of colon polyps, almost all the polyps disappeared.6 About a decade later, scientists from several laboratories took this clue further and identified two forms of the cyclooxygenase (COX) enzyme, COX-1 and COX-2. They found that COX-2 generates potent, hormone-like substances called prostaglandins that play a role in many physiological functions. One of these substances, prostaglandin E2 (PGE-2), was linked to the development of colon polyps.7 When COX-2 is expressed in a tumor‚ it allows new blood vessels to nourish the tumor, prevents tumor cells from dying, and increases the tumor’s ability to grow and spread (metastasize).8
|Colon cancer treatment using colonoscopy or sigmoidoscopy to remove polyps (inset). |
Thanks to the work of Waddell and other scientists, we now know that aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) are potent suppressors of colon polyps and colorectal cancer itself.9
The Chemoprevention Arsenal
While medical intervention is sometimes successful in treating colon cancer, a more powerful strategy for enhancing one’s health is to target prevention of the cancer altogether. Chemoprevention, the use of naturally occurring dietary supplements or synthetic agents to reduce the risk of cancer, shows promise for preventing, arresting, and reversing colon cancer development.
As noted earlier, aspirin and other NSAIDs are chemopreventive, as they suppress colon polyps and cancer. Dietary patterns also are controllable risk factors for the development of colon cancer. Folate, calcium, vitamin D, and selenium are among the dietary nutrients that offer protection against colon cancer. Diets rich in polyphenols such as green tea catechins and phytochemicals—including phenolics, flavonoids, and carotenoids from fresh fruits and vegetables—have also been shown to be chemopreventive.10 A diet high in fiber, particularly from grains, cereals, and fruits, may be associated with a decreased risk of colon cancer.11 Moreover, specialized plant compounds such as resveratrol and curcumin show promise in protecting against colon cancer.12,13
Folic acid. Comprehensive studies have linked a high intake of dietary or supplemental folate and high blood folate levels with a reduced risk of colon cancer. Cumulative data suggest that people who have the highest dietary folate intake have an approximately 40% lower risk of colon cancer compared to those with the lowest folate intake.14
Folate, or folic acid, is important for DNA synthesis and repair, and plays a key role in recycling the amino acid homocysteine into methionine, which the body uses as a building block in manufacturing new proteins. Moreover, the production of S-adenosyl-L-meth-ionine (SAMe), which is crucial for normal DNA methylation and gene expression, depends entirely on folic acid. Some scientists now believe that folate deficiency may increase the risk of malignancy by disturbing these pathways.15
Many studies support the use of folic acid supplementation in preventing colon cancer. For example, data from Harvard’s Health Professionals Follow-up Study, an ongoing study evaluating the link between nutrition and serious illness in 51,529 male professionals, showed a significantly reduced risk of colon cancer in men who used multivitamins with folic acid for more than 10 years compared to those who did not take folic acid.16
Similarly, in the Harvard Nurses’ Health Study, an observational study that followed more than 85,000 nurses from 1976 to 1994, scientists established that women who used multivitamins containing folic acid had a significantly lower chance of developing colorectal cancer. Researchers reported only 15 new cases of colon cancer per 10,000 women aged 55 to 69 years who used folic acid supplements, in contrast to 68 cases of colon cancer per 10,000 in those who did not supplement with folic acid—a risk reduction of over 75%.17 Folic acid supplementation is especially important for those who drink moderate amounts of alcohol, as alcohol blocks the absorption of folic acid and inactivates circulating folate, increasing the risk of colon cancer.18
Calcium. A wealth of evidence supports calcium’s role in colon cancer prevention. Dr. Harold Newmark, a Rutgers University-based authority on cancer prevention, has called on the FDA to require the addition of calcium and vitamin D to all cereal-grain products. In a recent article in the American Journal of Clinical Nutrition, Newmark wrote that the addition of these two nutrients could reduce colon cancer deaths by 20%, saving about 11,000 American lives and over $1 billion in US health care costs annually.19 Newmark also noted that the addition of vitamin D and calcium to cereal-grain products would likely reduce the incidence of osteoporotic fractures by 20%.19
The American College of Gastroenterology has recommended calcium supplementation for the primary or secondary prevention of colon adenomas.20 Harvard School of Public Health researchers have noted that higher total calcium intake is associated with a 27-42% decreased rate of cancer of the distal colon.21 Calcium in amounts of more than 700 mg daily appeared to offer minimal benefit in further risk reduction, according to the Harvard scientists.21 Calcium supplementation could reduce the number of colon cancer deaths by 16,000 annually, reports the American Cancer Society.
Evidence also suggests that calcium confers the most protection against the advanced polyps that are most strongly associated with invasive colorectal cancer. In the Calcium Polyp Prevention Study, researchers analyzed data from 930 patients (with an average age of 61) who had recently had a colorectal adenoma removed. The subjects took either a 1200-mg daily calcium supplement or placebo, then had follow-up colonoscopies at one and four years after starting supplementation.22 Calcium supplementation yielded an 18% lower risk of hyperplastic polyps and an 11% lower risk of tubular adenoma. Most significant, however, was a 35% reduction in histologically advanced neoplasms, an advanced form of colorectal lesion.22 The protective effect of calcium supplements was most pronounced among people with a high dietary intake of fiber and a low intake of fat.24 Calcium is thought to protect colon cells by precipitating fatty acids and bile acids that are potentially toxic to the colorectal epithelium.23
Vitamin D. While most experts acknowledge that calcium alone is chemopreventive against colon cancer, biochemical and biological evidence in cell culture systems suggests that exposure to calcium and vitamin D together may confer even more protection, reducing the tumor-forming properties of colon cancer cells.23
In late 2003, the Journal of the National Cancer Institute published groundbreaking research on vitamin D’s role in preventing colon cancer. In this study, researchers concluded that calcium and vitamin D work together to reduce the risk of colorectal cancer. Their four-year study followed 803 patients with a history of surgically removed colon adenoma polyps. Subjects who took 1200 mg of elemental calcium daily experienced a 31% occurrence of polyps compared to a 38% occurrence in the placebo group.24
Most revealingly, calcium supplements helped to prevent polyps only among participants with high levels of vitamin D levels in their bodies. Additionally, vitamin D levels were linked to reduced polyp recurrence only among those subjects who took calcium supplements. These findings strongly suggest that vitamin D and calcium have a synergistic anti-cancer effect in the bowel and may be far less effective when not used in combination.24