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Green Tea: Ten Cups a Day Does not Keep the Oncologist Away

Alexa Knorr




        The widespread consumption of green tea around the world has sparked scientists to become increasingly interested its potential health benefits. A website called “The Complete guide to Green Tea,” claims, “The benefits of green tea in a human body are so remarkable that it is believed that the key to a longer and healthier life may just be brewing in your cup!” ( Yes, green tea is said to be packed with antioxidants and it has been used medicinally in China for thousands of years, but is green tea really the miracle beverage preventing health risks like cancer? Many companies selling green tea advertise that the polyphenolic compounds in green tea, known as catechins, play a significant role in preventing cancer; however, many scientific studies exploring the relationship between cancer and green tea consumption have produced inconclusive results. There are numerous reasons for these ambiguous results including inconsistent consumption of tea, environmental and genetic influences, and human testing limitations. While some research in rodents show that consumption

of green tea is a protective factor against cancer, the overwhelming groups of epidemiological studies involving humans show no causational

relationship between green tea consumption and cancer prevention.


Background and Chemical Composition of Green Tea

        The usage and history of green tea travels back in time about 5,000 years in ancient China and since then, the beverage has gained popularity and has remained in daily Chinese diet. Today, tea is consumed by about one third of the world’s population (Chen, D. & Dou, Q.P. 2008).

        Green tea is derived from the Camellia sinensis evergreen, which is found in tropic and sub-tropic regions of the world. Because green tea is grown in diverse environments, there are numerous varieties and compositions of the tealeaves. Additionally, green tea is generally made by steaming fresh C. sinensis leaves then rolling and drying them without fermenting the constituents (Landau, J. M., Lambert, J. D., & Yang, C. S., 2006,).

        Of the many varieties of tea consumed throughout the world, green tea is studied the most because its dried leaves preserve its original polyphenolic compounds, called catechins. These polyphenolic structures “are characterized by  several hydroxyl groups on aromatic rings” (Landau,  J.M., et al, 2006, p. 597). Scientists are most  interested in a catechin called epigallocatechin gallate, denoted (-)-EGCG, which accounts for 50-80% of catechins in a typical 250 mL cup, and is thought, by some, to have chemoprotective attributes (Philips, B.J., Coyle, C.H., Morrisroe,  S.N., Chancellor, M.B., & Yoshimura, N., 2009). Because it is inexpensive, abundant, and nontoxic, green tea is very easy to study.


Website Advertisement Claims

        Websites, that have the goal of selling green tea products rather than providing scientifically supported information, make bold claims about connections between green tea consumption and cancer prevention even though they aren’t scientifically supported. One website, “,” clearly targets Americans as its marketing audience, yet in an attempt to portray a more authentic virtual Chinese atmosphere, the page is adorned by corny Asian calligraphy and bold neon colors. It is more than obvious that the sole purpose of this website is to sell green tea by the box, and in order to maximize sales, the webpage must quickly convince the population that green tea does serve a positive purpose for everyone. All of the brief claims and purposes of green tea are posted at the top of the home page in capital letters and the only links posted on the website lead to easy payment mechanisms that include the oh-so-fast-and-simple Paypal. In the middle and bottom regions of the home page, huge, bright images of the product itself beg the consumer to buy buy buy.

Chinese Green Tea Farm

        The first string of words on the webpage states, in red lettering, “ANCIENT CHINESE HEALTH SECRETS REVEALED!” By advertising something that is said to be a “secret,” the creator of the website is strategically attempting to entice the public eye with the historical mysteries of Chinese medicine in hopes to gain more green tea sales. This website also claims that, “Green Tea has been scientifically confirmed to lower cancer causing cells” ( From a marketing standpoint, having scientific support for a claim will  more likely turn nonbelievers in believers, or in more appropriate terms, nonbuyers to buyers. However, scientists conducting present research on green tea and cancer prevention would hotly challenge this statement because of the ambiguous results gained from numerous epidemiological studies.

Challenging Website Claims

        Interestingly, credits University of Purdue with finding that, “… a compound in green tea inhibits the growth of cancer cells” ( in order to help legitimize the websites health claims and increase green tea sales. Even though University of Purdue is a respectable source, it is likely that the sales website purposely left out a lot of important information concerning the results and methods of the research that would severely diminish convincing Americans that drinking green tea will reduce their probability of being diagnosed with cancer. For example, most current research, providing conclusive evidence that green tea promotes cancer prevention, is completed by using mice, or rats as study subjects. More specifically, studies have shown that green tea can inhibit tumor formation in the lung at several stages of development in mice (Yang, C.S., & Wang, Z.Y., 1993). However, at the same time, a similar mouse study found no relation between green tea consumption and the inhibition of tumor formation in the lung (Witschi, H., Espiritu, I., Yu, M., & Willits, N.H, 1998). Therefore, even evidence that is thought to be conclusive in mice, is proving to be somewhat nebulous. 

Studies of Humans Versus Rodents

        Even though there are numerous animal studies that demonstrate potential protective effects against cancer, “Strong evidence for such beneficial health effects in humans is scarce” (Landau, J. M., et al. 2006, p. 597). The differentiation in evidence between human and rodent studies have to do with the metabolism of catechins and the amount and concentration of green tea used in these studies. Wu, A.H. et al. (2003), found that in a population of Asian Americans those with at least one low activity genetic allele, called catechol-O-methyltransferase, had lower risk of developing breast cancer because they “…metabolize tea polyphenols less efficiently and, therefore, had prolonged exposure to these compounds” (Wu, A.H., Yu, M.C, Tseng, C.C, Hankin, J. & Pike, M.C., 2003, p. 575). The authors of this article affirm that green tea polyphenols may serve as a protective factor against cancer in these Asian Americans, but of course we aren’t all made up of the same genetic code. Even so, it is useful to know that green tea polyphenols may have chemoprotective purposes when it lasts in the body longer. Again, this idea would require more comprehensive studies.

        It is also important to consider that there may be more conclusive evidence for the effects of green tea on cancer formation in animals because of the fact that scientists can give lab mice and rats treatments that cannot always be replicated with human subjects because it is dangerous and unethical. Often in lab experiments, rodents receive a much higher dose of green tea than would be used comparatively with humans because humans tend to show adverse bodily reactions after consuming larger amounts of green                                                                                                                                                                      tea (Landau, J. M., et al. 2006). Humans have been tested in laboratory settings where they received higher doses of green tea in its pure form, yet doses over 800mg led to         

                                                         feelings of nausea, vomiting, insomnia, fatigue, diarrhea, abdominal pain, and

 confusion (Chow, H.H., Cai, Y., Hakim,  I., Crowell, J.A., Shahi, F., Brooks, C.A.,

Dorr, R., Hara, Y., & Alberts, D.S 2001). These results make research on  humans limited and therefore, it is likely  

that the work done by University of Purdue, was completed using lab rats, and of course, we would buy a product

because of the benefits found solely in  rodents.


What the FDA Says

        Since the passing of the Pure Food and Drug’s Act in 1906, the Food and Drug Administration has been the primary regulator of consumables that are put on the market. The FDA initiated regulation laws in order to protect the public from false advertisement and to insure that what is being sold in grocery stores and pharmacies is absent of hazardous ingredients. The FDA states “Some products — such as new drugs and complex medical devices — must be proven safe and effective before companies can put them on the market” ( Considering green tea, safety is not of concern to the FDA because it has been part of the human diet for a centuries and it is the most consumed beverage in the world behind water (Philips, B.J et al. 2009) Rather, the FDA is interested in reviewing the studies that claim that green tea is an effective cancer inhibitor.

        The FDA doesn’t produce research and design experiments to study new products. Instead, the FDA comes to conclusions about whether or not a product is safe or effective by reviewing, “…the results of laboratory, animal and human clinical testing done by companies…” (

In this reviewing process, the FDA instills

confidence in the public by assuring that

products being sold have been scientifically

tested and proved to be safe and effective.

Thus far, the FDA has not made that assurance

about the effectiveness of green tea as a cancer



        The continual oversight of the FDA on health claims makes it an omnipotent force in deciding whether or not public health practices, like drinking green tea, are empirically supported. In 2005, the FDA made an announcement about research results studying health claims that, “green tea may reduce the risk of certain types of cancer” ( In their review, the FDA presented two sets of data. First it was noted that several studies outright didn’t find conclusive evidence to support the claim and a weak, limited study showed that it may be possible that green tea consumption may reduce cancer risk. The second set of data included two more weak and limited studies that had conflicting results. Therefore, it isn’t surprising that the FDA concluded that, “It is highly unlikely that green tea reduces the risk of [breast and prostate] cancer.” The FDA also came to the conclusion that besides prostate and breast cancer, there is no empirical evidence to support claims that green tea consumption reduces the risk of any type of cancer.

A Study From Asia

        Since there are limitations in green tea consumption in western populations, scientists have become more interested in studying Asian populations. The typical Chinese diet includes, around five cups of green tea per day and in some regions, men and women drink up to ten cups of tea daily (Landau, J.M. 2006). As a result, it isn’t surprising that the few studies that do claim that cancer prevention is linked to green tea consumption are found in Asian cohorts. One particular study examining green tea’s effect on breast cancer, contends that, “It seems probable that changes in lifestyle, including a trend away from the tradition of drinking green tea, are playing a role in the movement of breast cancer rates in China toward those of Western countries” (Zhang, M., D’Arcy, C., Holman, J., Huangl, J., & Xiel, X. 2007, p. 1076). Because breast cancer is the most common cancer among female populations in the world, Zhang, finds it likely that that connection between lack of green tea consumption in western populations and higher breast cancer cases is a strong indicator that components in green tea do indeed serve as a protective factor the Chinese population.

        In his case-control study, Zhang recruited1009 women diagnosed with “invasive ductal carcinomas” of the breast along with a control group of 1009 cancer free women for research participation. The women completed “a validated and reliable questionnaire” that collected information on factors such as lifestyle, demographics, education, physical activity, hormonal status, health history, and food and tea consumption (Zhang, M. et al. 2007). There was an additional questionnaire targeting type and preparation of tea, along with the frequency and duration of tea consumption. 


      Zhang M. et al. (2007) found that, “The risk of breast cancer declined with increasing quantity, duration and frequency of green tea consumed” (p. 1075). Therefore, these results lead the researchers to conclude that green tea consumption does, in fact, affect the risk of breast cancer. Even so, there are likely to be possible confounds in this particular study that influenced the causation in decreased cancer. Specifically, Zhang explains that, those who included green tea in their daily diets were also typically living in urban areas, they were better educated, and they consumed healthier foods. “Thus, any residual confounding from these lifestyle factors would have affected the apparent protective effect of green tea” (Zhang, M. et al. 2007, p. 1077). So it may be possible that green tea isn’t related to cancer prevention, but rather a healthier lifestyle in general.

      In response to the common knowledge in the scientific community that green tea’s connection to cancer prevention isn’t strongly supported, Zhang et al. (2007) contends that his research “…elaborates on the inconclusive evidence on tea and breast cancer in previous studies since most of the studies yielding null results were conducted in Western populations that consumed exclusively black tea” (p. 1074). Now it is important to question whether it is green tea consumption or other lifestyle, cultural, and socioeconomic differences between Western and Asian populations that may be the true underlying cause of cancer rates. It is quite clear that, “More research to closely examine the relationship between tea consumption and breast cancer risk is warranted” (Zhang, M. et al. 2007, p. 1077). Even in a population promising more conclusive results, scientists studying the relation between cancer prevention and green tea consumption, continue to find ambiguous and somewhat disappointing results.


      Simple put, studying green tea’s cancer-preventative features is difficult. The never-ending combination of limiting, confounding, environmental, and natural factors make it necessary to continue research by examining diverse populations and manipulating interesting variables. Adding to the strain on controlling experimentation is the fact that green tea is a very diverse beverage in that it can be prepared, and processed in numerous ways and it is grown is many geographic locations and conditions. These inconsistent components ultimately effect the concentration of polyphenols in green tea and make the overall study of its consumption seemingly impossible. It isn’t fair to say that green tea has no relation to cancer prevention. If scientists found absolutely no hint of causational evidence between the independent and dependant factors, they wouldn’t be interested in further studies. However, because we have an idea of the possibilities, it is up to scientists to tweak their research and make it applicable to humans. 






Chen, D. & Dou, Q.P. (2008). Tea polyphenols and their roles in cancer prevention and       chemotherapy. International Journal of Molecular Sciences 9(7), 1196–1206.


Chow, H.H., Cai, Y., Hakim, I., Crowell, J.A., Shahi, F., Brooks, C.A., Dorr, R., Hara,     Y., & Alberts, D.S. (2001). Phase I pharmacokinetic study of tea polyprophenols       following single-dose administration of epigallocatechin gallate and polyphenon E.      Cancer Epidemiol Biomarkers Prev. 10(1), 53-38.


Landau, J. M., Lambert, J. D., & Yang, C. S. (2007). Green tea. Nutritional Oncology 35,       597-606.


Philips, B.J., Coyle, C.H., Morrisroe,  S.N., Chancellor, M.B., & Yoshimura, N. (2009).

     Induction of apoptosis in human bladder cells by green tea catechins. Biomedical       Research 30(4), 207-215.


U.S. Food and Drug Administration. FDA issues information for consumers about claims for green tea and certain cancers. June, 22 2009. Retrieved October 4th.


Witschi, H., Espiritu, I., Yu, M., & Willits, N.H. (1998). The effects of phenethyl       isothiocyanate, N-acetylcysteine and green tea on tobacco smoke-induced lung       tumors in strain A/J mice. Carcinogenesis 19(10), 1789-1794.


Wu, A.H., Yu, M.C, Tseng, C.C, Hankin, J. & Pike, M.C. (2003). Green tea and risk of       breast cancer in Asian-American women. Int J Cancer 106, 574-579.


Yang, C.S., & Wang, Z.Y. (1993). Tea and cancer: a review. J Natl Cancer Inst 58, 1038-      1049.


Zhang, M., D’Arcy, C., Holman, J., Huangl, J., & Xiel, X. (2007). Green tea and the       prevention of breast cancer: a case-control study in Southeast China.   Carcinogenesis 28(5), 1074-1078.









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