by Craig Weatherby and Linda Sparrow
The evidence that green tea possesses anti-cancer powers is mixed, and varies by cancer type.
A recent evidence review suggests that the evidence supporting any anti-cancer properties of green tea remains inconclusive.
As lead review author Katja Boehm, said, “Despite the large number of included studies, the jury still seems to be out on the question of whether green tea can in fact prevent the development of various cancer types” (HDN 2009; CC 2009).
However, in a recent clinical study of oral cancer, green tea extract produced beneficial effects in six out of 10 of the participants taking the highest doses.
And a recent population study linked frequent tea drinking to a 40 to 50 percent cut in rates of blood and lymph cancers.
Let's take at these two new studies... and what the National Cancer Institute says about the potential of tea as an anti-cancer ally.
Population study links tea habit to lower rates of blood and lymph cancers
Researchers at the Tohoku University School of Medicine in Japan analyzed data concerning the tea-drinking habits of 41,761 people, and then followed their health status for nine years (Naganuma T et al. 2009).
The results showed that, compared to those who drank one or fewer cups per day, people who drank five or more cups of green tea per day were 24 percent less likely to develop bone marrow cancer, 42 percent less likely to develop blood cancer, 48 percent less likely to develop lymph-gland tumors.
Green tea extracts curb oral cancer in clinical study
According to the American Cancer Society, more than 35,720 people are diagnosed with oral and/or pharynx cancer annually, and the five-year survival rate is less than 50 percent.
And the results of a new study from the University of Texas M. D. Anderson Cancer Center indicate that extracts from green tea may prevent the formation of mouth cancers in people with risk signs of the disease (Tsao AS et al. 2009).
This “phase II dose-finding” trial followed 41 people with a condition called oral leukoplakia, which is a sign of oral cancer risk (The study was funded by Ito En, the company that produced the green tea extract).
The participants were assigned to receive either a daily placebo pill, or daily pills containing one of three doses of green tea extract: 500 milligrams per meter squared of body mass (mg/m2), 750 mg/m2, or 1,000 mg/m2.
The researchers took oral tissue biopsies, which, as co-researcher Anne Tsao, M.D. said, “…allowed us to learn that not only did the green tea extract appear to have benefit for some patients, but pointed to anti-angiogenic effects as a potential mechanism of action” (UTMDA 2009).
(Angiogenesis is a term describing growth of new blood vessels, and if you can keep tumors from tapping into the body's blood supply, they will stagnate or die. This principle has led to development of cancer drugs with anti-angiogenic effects.)
The results of the study were encouraging:
- Almost 60 percent of people taking the two highest doses of the green tea extracts had a clinical response.
- Just over 36 percent of people in the lowest extract dose group had a clinical response, compared to 18 percent in the placebo group.
“The extract's lack of toxicity is attractive – in prevention trials, it's very important to remember that these are otherwise healthy individuals and we need to ensure that agents studied produce no harm,” he added (UTMDA 2009).
Future studies in high-risk people are needed to investigate the effects of longer supplementation periods.
The anti-cancer properties of polyphenols
According to the National Cancer Institute's Fact Sheet on Tea and Cancer Prevention, there's substantial evidence that tea possesses anti-cancer powers (NIH 2009):
- The antioxidants found in tea—called catechins—may selectively inhibit the growth of cancer.
- In laboratory studies using animals, catechins scavenged oxidants before cell damage occurred, reduced the number and size of tumors, and inhibited the growth of cancer cells.
- However, human studies have proven more contradictory, perhaps due to such factors as variances in diet, environments, and populations.
- National Cancer Institute researchers are investigating the therapeutic and preventive use of tea catechins against a variety of cancers.
Green tea contains between 30 and 40 percent water-extractable polyphenols, while black tea (green tea that's been oxidized by fermentation) contains between 3 and 10 percent.
But tea isn't the only source of beneficial polyphenols, which abound in berries, cocoa, grapes, and culinary herbs and spices.
In particular, the yellow pigment in turmeric—called curcumin—contains polyphenols (curcuminoids) that appear to possess particularly powerful anti-cancer properties.
As the authors of a recent evidence review wrote, “...curcumin has been reported to have immense potentiality for being used in cancer chemotherapy because of its control over the machineries of cell survival, proliferation, invasion, and angiogenesis. The mechanisms implicated are diverse and appear to involve a combination of cell signaling pathways at multiple levels” (Das T et al. 2009).
Stay tuned for more news on this topic.
- Boehm K, Borrelli F, Ernst E, Habacher G, Hung SK, Milazzo S, Horneber M. Green tea (Camellia sinensis) for the prevention of cancer. Cochrane Database of Systematic Reviews 2009, Issue 3. Art. No.: CD005004. DOI: 10.1002/14651858.CD005004.pub2.
- Das T, Sa G, Saha B, Das K. Multifocal signal modulation therapy of cancer: ancient weapon, modern targets. Mol Cell Biochem. 2009 Oct 14. [Epub ahead of print]
- HealthDay News (HDN). No Firm Evidence Green Tea Helps Prevent Cancer. July 21, 2009. Accessed at http://health.usnews.com/articles/health/healthday/2009/07/21/no-firm-evidence-green-tea-helps-prevent-cancer.html
- Naganuma T, Kuriyama S, Kakizaki M, Sone T, Nakaya N, Ohmori-Matsuda K, Hozawa A, Nishino Y, Tsuji I. Green Tea Consumption and Hematologic Malignancies in Japan: The Ohsaki Study. Am J Epidemiol. 29 Jul 2009.
- National Cancer Institute (NCI). Fact Sheet on Tea and Cancer Prevention Accessed at http://www.cancer.gov/cancertopics/factsheet/prevention/tea
- Sartippour MR, Shao ZM, Heber D, Beatty P, Zhang L, Liu C, Ellis L, Liu W, Go VL, Brooks MN. Green tea inhibits vascular endothelial growth factor (VEGF) induction in human breast cancer cells. J Nutr. 2002 Aug;132(8):2307-11.
- Shanafelt T, Call T, Zent C, LaPlant B, Bowen D, Roos M, Secreto C, Ghosh A, Kabat B, Lee M, Yang C, Jelinek D, Erlichman C, Kay N. Phase I Trial of Daily Oral Polyphenon E in Patients With Asymptomatic Rai Stage 0 to II Chronic Lymphocytic Leukemia. Journal of Clinical Oncology. 10 August 2009, Vol 27, No 23: pp. 3808-3814.
- The Cochrane Collaboration (CC). Green tea (Camellia sinensis) for the prevention of cancer. Accessed November 9, 2009 at http://www.cochrane.org/reviews/en/ab005004.html
- Tsao AS, Liu D, Martin J, Tang XM, Lee JJ, El-Naggar AK, Wistuba I, Culotta KS, Mao L, Gillenwater A, Sagesaka YM, Hong WK, Papadimitrakopoulou V. Phase II randomized, placebo-controlled trial of green tea extract in patients with high-risk oral premalignant lesions. Cancer Prev Res (Phila Pa). 2009 Nov;2(11):931-41.