Green Tea: The Most Studied Anti-Cancer PlantThere are now more active clinical trials using green tea against cancer than any other plant extract: twenty-two trials are currently running (fifteen are still recruiting). PubMed now lists nearly 1600 peer-reviewed research articles, which mention "green tea" and "cancer," and the list is growing at about 150 per year. Despite all this research, a clear-cut recommendation for green tea intake has been frustrated by several factors. Population studies have based their data on "cups per day" consumed, but the amount of cancer-fighting polyphenols per cup changes dramatically according to brewing time, amount used per cup, and type of tea (sencha, bancha, genmaicha etc.). Even the same tea will yield different EGCG contents according to time of harvest and position on the plant from which the leaves are harvested.
What Exactly is a Cup of Green Tea?Because of these differences, a common basis is needed among researchers. Therefore the standard Japanese-style cup of green tea has been defined in some research papers as being 120 ml in volume and containing 50 mg EGCG (among other polyphenols). This is somewhat less than the USDA's current data, which estimates a 120 ml cup of tea to contain 77 mg EGCG.
Green Tea Consumption Versus Cancer RiskKeeping the above definitions in mind, recent meta-studies show the following levels of consumption may reduce cancer risk as indicated.
5 cups/day or more:
- 56% less oral cancer
- 54% less prostate cancer
- 42% less liver cancer
- 22% less endometrial cancer
2 cups/day or more:
- 18% less lung cancer (for general population)
1 cup/day or more:
- 60% less lung cancer (for female non-smokers)
- 44% less ovarian cancer
Most people taking part in the above studies consumed a maximum of 5 cups per day (very few consumed 10 or more), which limits how much risk reduction was experienced. This level still offers good protection from several major cancers. The risk reduction is not so clear yet for cancers of the breast, colon, stomach or pancreas - they may require even higher levels of consumption. Note: smoking seriously decreases the benefits of green tea against lung cancer, which is why non-smoking women see a 60% risk reduction with just 1 cup daily; whereas, the general population (smokers included) need 2 cups daily just to realize an 18% risk reduction. For most cancers, there is a "dose-response" relationship in which more green tea leads to greater reduction of cancer risk. For example, every 2 additional cups daily leads to an additional risk reduction of 18% for lung cancer and 22% for prostate cancer.
Green Tea for Cancer Prevention: At Least 5 Cups DailyTherefore 5 cups of green tea daily appears to be the minimum consumption level in order to achieve meaningful reduction of cancer risk. If you don't want caffeine, decaf green tea is an option, but it contains only about one third the EGCG content per cup compared to regular green tea. If you want a more steady, reliable intake of cancer-fighting polyphenols than brewed tea provides, then consider green tea supplements standardized to at least 250mg of EGCG per dose (according to the Japanese standard cup).
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