Green Tea and Cancer
(9/1914)- Even though this article was written by Harold back in 2006, we at therubins thought it would be worthwhile to our viewers to take a look at it again. The percentages contained in the article may have changed, but we think the premises behind the article may still be true today
(April 18, 2006) Green tea continues to be one of the shining stars in the liturgy of complimentary and alternative supplement adherents to aid in a variety of disorders associated with the elderly. What is it that makes green tea different from other kinds of tea? To answer this question, one needs to know something about the manufacturing process of tea.
Teas are classified into three major categories or types: non-fermented green tea; semi-fermented oolong tea and fermented black or red teas. Tea is second to water as the most common drink in the world. Black tea is the most common, making up 76-78% of the produced and consumed tea. Twenty to twenty-two percent of tea produced and consumed is green tea, and less than 2% is oolong tea.
The chemical contents of tea vary with the soil it is grown in, the time of year it is harvested and the manufacturing process involved. Green tea is produced by drying and steaming the fresh leaves to inactivate the polyphenol oxidase, and thus, non-oxidation occurs. Oolong tea is produced when the fresh tea leaves are subject to a partial fermentation stage before drying. The most common black tea undergoes a post-harvest fermentation stage before drying and steaming, using an oxidation process catalyzed by polyphenol oxidase. Final factor in the effect of tea on health would be the amount consumed and the nature of the chemical reactions in the body.
All teas contain polyphenols. Polyphenols act as antioxidants in vitro an in vivo studies. They protect cells and body chemicals against damage caused by free radicals, reactive atoms that contribute to tissue damage in the body.
Flavonoids are polyphenolic compounds that are ubiquitous in nature and are categorized, according to chemical structure, into flavonols, flavones, flavanones, isoflavones, catechins, anthocyanidins and chalcones. Over 4,000 flavonoids have been identified, many of which occur in fruits, vegetables and beverages (tea, coffee, beer, wine and fruit drinks).
The flavonoids have aroused considerable interest recently because of their potential beneficial effects on human health-they have been reported to have antiviral, anti-allergic, antiplatelet, anti-inflammatory, antitumor and antioxidant activities." (Linus Pauling Institute site http://lpi.oregonstate.edu/f-w00/flavonoid.html, visited April 18, 2006.) Catechins are the main flavonoid compound in green tea.
The capacity of flavonoids to act as antioxidants depends upon their molecular structure. The position of hydroxyl groups and other features in the chemical structure of flavonoids are important for their antioxidant and free radical scavenging activities. Quercetin, the most abundant dietary flavonol, is a potent antioxidant because it has all the right structural features for free radical scavenging activity.
The site, http://encyclopedia.thefreedictionary.com/Quercetin visited on April 18, 2006 contained this information on Quercetin.
"Quercetin is a flavonoid that forms the "backbone" for many other flavonoids, including the citrus flavonoids rutin, hesperidin, naringin and tangeritin. Quercetin is found to be the most active of the flavonoids in studies, and many medicinal plants owe much of their activity to their high quercetin content. Quercetin has demonstrated significant anti-inflammatory activity because of direct inhibition of several initial processes of inflammation. For example, it inhibits both the manufacture and release of histamine and other allergic/inflammatory mediators. In addition, it exerts potent antioxidant activity and vitamin C-sparing action." The main flavonoids in green tea are four catechins (epigallocatechin-3-gallate (EGCG); epigallocatechin (EGC); epicatechin-3-gallate (ECG); epicatechin (EC) . Green tea also contains gallic acid, and other phenolic acids such as chlorogenic acid, and caffeic acid, as well as flavonids such as kaemperol, myricetin, and quercetin.
The most recent review of the beneficial effects of green tea that we have come across appears in the Journal of the American College of Nutrition 2006;25(2):79-99. This review by Carmen Cabrera, Ph.D et al concludes: "Recent studies suggest green tea may contribute to reduce the risk of cardiovascular disease and cancer, and have other beneficial effects on health." (Italics added.) Dr. Cabreraís review uses the cautious words "may contribute" instead of a more positive affirmation of the role of green tea in promoting health or prevention of human disease.
We would suggest that more work needs to be done with controlled, double blind studies before bellowing to the world the "beneficial" effects of green tea. The present studies are still not robust for conclusive results, especially when it comes to standardizing the contents of the manufactured tea. With this said, there is no reason to not take green tea as an added component to your armentarium to fight the diseases of aging, unless one is allergic to any of the many compounds in green tea or there is a potential synergistic effect with some of the medications you are taking.
(12/29/99)- Many of our readers send us e-mails to suggest that we write articles about particular topics. Recently, a number of readers have asked us about herbs and dietary supplements, and we have responded by writing articles about Gingko Biloba and St, Johnís Wort. Just today, December 29, while reviewing the November issue of Nature Medicine (vol. 5, #1, 1999), I noticed a letter to the editor from a group of Italian researchers that may be of interest to our readers. The letter to the editor was entitled "Tumor Invasion: Molecular Stresses Blunted by Green Tea."
These researchers pointed out that the main flavinol of green tea was called epigallocatechin-3-gallate (EGCG) and that it inhibits urokinase, one of the hydrolases implicated in tumor invasion.
They indicate that their finding "show that micromolar EGCG inhibits tumor cell invasion and directly suppresses the activity of MMP-2 and MMP-9, both isomers of metalloproteinase (MMP), two of the proteases most frequently over-expressed in cancer and angiogenesis, and essential in cutting through basement membrane barriers." (p. 1206).
They claim that the consumption of 2 or 3 cups of green tea (0.1-0.3m M) are sufficient to exert such a promising biological activity. Green tea "exerts its beneficial effects against cancer by impairing tumor invasion and nourishment through direct inhibition of two gelatinases that open up pathways for cell migration. Furthermore, in addition to having a preventative role, EGCG may be effective in combination with angiostatin (inhibitor of endothelial cell proliferation) in a direct action clinical treatment." (p. 1206)
The writers of this letter list 6 references for further information including an article from Nature 1999, 398, 381 written by Cao & Cao called "Angiogenesis inhibited by drinking tea."
Thus, it would appear that there is evidence to support use of dietary
supplements or herbs in combating a devastating illness. However, this
should only be done in consultation with your physician.
INFORMATIVE AND PERSONAL ARTICLE ON PRACTICAL SUGGESTIONS WHEN SELECTING A
NURSING HOME SEE OUR ARTICLE " How to Select a Nursing
By Harold Rubin, MS, ABD, CRC, Guest Lecturer
updated September 19, 2014