Colon Cancer

Green tea and black tea (Camellia sinensis) have both been studied to determine whether they cause or prevent cancer. The evidence on the protective effect of either type of tea is inconsistent.^{1,2,3,4,5,6,7,8}

A number of preliminary studies have shown an association between drinking green tea and a reduced risk of some types of cancer,^1,2,3,4 including colon cancer.^5,14 In contrast, preliminary studies found that consumers of black tea do not appear to have a reduced risk of any type of cancer.^6,7,8,18

Selenium has been reported to have diverse anticancer actions.^11,12 Selenium inhibits cancer in animals.¹³ Low soil levels of selenium, probably associated with low dietary intake, have been associated with increased cancer incidence in humans.¹⁴ Blood levels of selenium have been reported to be low in patients with a variety of cancers,^{15,16,17,18,19,20,21,22} including colon cancer.²³ In preliminary reports, people with the lowest blood levels of selenium had between 3.8 and 5.8 times the risk of dying from cancer compared with those who had the highest selenium levels.^24,25

The strongest evidence supporting the anticancer effects of selenium supplementation comes from a double-blind trial of 1,312 Americans with a history of skin cancer who were treated with 200 mcg of yeast-based selenium per day or placebo for 4.5 years, then followed for an additional two years.²⁶ Although no decrease in skin cancers occurred, a dramatic 50% reduction in overall cancer deaths and a 37% reduction in total cancer incidence were observed. A statistically significant 58% decrease in cancers of the colon and rectum was reported.

Caution: Calcium supplements should be avoided by prostate cancer patients.

Through a variety of mechanisms, calcium may have anticancer actions within the colon. Most,^27,28,29 but not all,³⁰ preliminary studies have found associations between taking calcium supplements and a reduced risk of colon cancer or precancerous conditions in the colon. In double-blind trials, calcium supplementation has significantly protected against precancerous changes in the colon in some,^31,32 but not all, reports.^33,34 While most evidence examining the ability of calcium supplementation to help prevent colon cancer appears hopeful, no research findings yet support the use of calcium supplements in people already diagnosed with colon cancer.

Preliminary animal and test tube research suggests that CLA might reduce the risk of cancers at several sites, including breast, prostate, colorectal, lung, skin, and stomach.^35,36,37,38 One preliminary study in humans suggests that increasing CLA intake may reduce the risk of colorectal cancer.³⁹

People with ulcerative colitis (UC) are at increased risk for colon cancer. Many patients with this disease take the drug sulfasalazine, which depletes folic acid.⁴³ In a preliminary report, patients with long-standing UC who took folic acid supplements (at least 400 mcg per day) had a 62% lower incidence of colon cancer or precancerous changes in the colon, compared with those who did not supplement with folic acid.⁴⁴ Although this difference was not statistically significant, the researchers recommended that people who take sulfasalazine should supplement with folic acid to potentially reduce the risk of colon cancer.⁴⁴

As dietary folate increases, the risks of precancerous polyps in the colon⁴⁶ and colon cancer itself decrease, according to some,⁴⁷ but not all, reports.⁴⁸ In one study, women who had taken folic acid supplements had a statistically significant 75% reduction in the risk of colon cancer, compared with women not taking folic acid supplements, but only when they had been supplementing with folic acid for more than 15 years.⁴⁹ In another report, the association between dietary folate and protection from precancerous polyps grew much stronger when use of folic acid supplements was considered (as opposed to studying only folate intake from food).⁴⁶ However, one double-blind study found that supplementing with 1 mg of folic acid per day for three to eight years did not prevent recurrences of precancerous polyps in people who had already had at least one polyp.⁵¹

The protection from colon cancer associated with high intake of folate has been reported to occur more in consumers of alcohol than in nondrinkers.⁵² This finding fits well with evidence that folate reverses damage to DNA caused by alcohol consumption.⁵³ Damaged DNA can lead to abnormal cellular replication—a step toward cancer.

Women, but not men, who took vitamin C supplements were reported to have a reduced risk of colon cancer, according to a preliminary report.⁵²

Familial polyposis is a disease that usually leads to colon cancer. In a double-blind study, supplementation with 3 grams per day of vitamin C for nine months led to a reduction in the number of precancerous polyps in people with familial polyposis.⁵³ In another controlled trial, combining vitamin C with vitamin A and vitamin E led to a dramatic reduction in the recurrence of adenomatous polyps—another precancerous condition of the colon.⁵⁴ However, other trials attempting to prevent recurrence of adenomatous polyps using vitamin C alone or in combination with other vitamins have reported no therapeutic effect⁵⁵ or only weak trends favoring the group given supplements.^56,57

Therefore, the ability of vitamin C supplementation to reduce recurrences of precancerous polyps remains unproven. Whether long-term supplementation with vitamin C would directly help in the prevention of colon cancer has not yet been studied.

Ultraviolet light from sun exposure increases the risk of skin cancers and melanoma. Nonetheless, where sun exposure is low, rates of several cancers have been reported to be high.^58,59,60 An association between greater sun exposure and a reduced risk of colon cancer has appeared in some,⁶¹ but not all, studies.⁶²

In preliminary reports, people who take vitamin D supplements have been reported to be at low risk for colon cancer, though the differences between supplement takers and others might have been due to chance.^62,64 More research is needed to determine whether vitamin D supplements may be useful in connection with the prevention of colon cancer.