A large and growing body of evidence (from preclinical and human trials) suggests that there may be a protective effect of green tea against various cancer types. Still, the data are not conclusive.
Background: Tea may help lower the risk of cancer of several types (including lung, prostate, breast, gastrointestinal tract, and skin), at least according to laboratory models. This may be due to its antioxidant effects, enhancement of some chemotherapy agents, or the blocking of growth-factor signaling. The epidemiological data is less clear, however.
Tea Components: Tea has many bioactive compounds, including flavonols, catechins, lignans, and phenolic acids.
Human Data: Jian-Min Yuan, MD, PhD of the University of Minnesota (USA) recently reviewed epidemiological studies examining the association between esophagus cancer and green tea consumption in Asian populations, which have a high incidence of esophageal cancer and a high consumption of green tea. Of 15 studies, 6 reported a significantly reduced risk for esophagus cancer associated with high amounts of green tea consumption, 4 reported a lower but non-significant risk, 3 reported a significantly positive association between tea consumption and risk, and 2 report no association. Other reviews have reported similar inconsistencies for different cancer types, including prostate, breast, colon, and liver cancer.
Early Cancer: In his review, Joshua Lambert, PhD (Pennsylvania State University, USA) looked at human and experimental studies. He notes that green tea and green tea catechins have been shown to block tumor formation. Although not as well-studied, the same may be true of black tea. Unfortunately, the number of human studies directly examining green tea and tumor progression is limited.
Green tea may reduce the probability of pre-cancer in the prostate (prostatic intraepithelial neoplasia) progressing to prostate cancer. After a year of daily supplements with green tea catechins 600mg versus placebo (inactive substance), fewer men in the green tea group progress to cancer, compared to the placebo group (9% versus 30%) (Cancer Research 2006;66:1234-1240). Similar results were seen in a study looking at green tea and oral premalignant lesions and the future occurrence of colorectal adenoma (benign tumor that can become cancer), finding a benefit to green tea (Cancer Epidemiol Biomarkers Prev 2008;17:3020-3025).
My Take: We need phase 2 intervention studies to bettwe understand the biologic mechanisms related to some of the known cancer risk pathways in humans. Ultimately, we would like to have phase 3, randomized intervention trials that look at cancer incidence and mortality. Such studies would take a long time, and much funding. The laboratory doses of tea polyphenols is much higher than what we can consume through diet. And, we need to control for tea temperature, as very high temperatures may actually increase the risk of esophagus cancer. For those who want to incorporate green tea, check with your health care provider, as green tea substances can interact with some drugs (including, but not limited to Velcade/bortezomib). My personal bias is to get beneficial ingredients through diet, rather than supplements, in part because we do not know which specific tea polyphenols provide the potential protective effect, or how much is needed (there can be side effects, especially at higher doses). I’m Dr. Michael Hunter and, with apologies to my Japanese family members, I do not like green tea (or green eggs and ham, for that matter)!
The small print: The material presented herein is informational only, and is not designed to provide specific guidance for an individual. Please check with a valued health care provider with any questions or concerns. As for me, I am a Harvard- , Yale- and UPenn-educated radiation oncologist, and I practice in the Seattle, WA (USA) area. I feel genuinely privileged to be able to share with you. If you enjoyed today’s offering, please consider clicking the follow button at the bottom of this page.
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References: Green Tea for Cancer Prevention: A Mixed Bag. Medscape Nov 12, 2013.