Green tea is a popular beverage for many Americans. According to the Linus Pauling Institute at Oregon State University, water is the only beverage that people drink more frequently, worldwide, than tea. In addition to the beverage, people may take green tea as a supplement called green tea extract. In either form, green tea can be upsetting to the stomach.
Green Tea
Like all true teas, green tea is derived from the leaves of the Camellia sinensis plant, which is cultivated in semi-tropical areas of Asia and Africa. Tea may be processed in different ways; the processing includes rolling, oxidation, steaming or firing and drying. Each process results in a tea that has slightly different properties. For green tea, the leaves are withered prior to steaming or firing, but are not allowed to oxidize.
Green Tea Chemicals
Green tea is not just a simple beverage, but a complex liquid that contains many bioactive chemicals such as flavonoids, fluoride, caffeine and tannins. Among the green tea flavonoids are catechins, chemical compounds that develop during the oxidation process. Green tea has higher amounts of flavonoids called polyphenols, which have antioxidant properties, than other types of tea.
Caffeine
Unless they are decaffeinated, all teas contain caffeine. Green tea contains about 9 to 50 mg of caffeine per 8-oz. cup. This bitter-tasting stimulant can also irritate the gastrointestinal tract. In one study reported in the March 2003 issue of "Cancer," patients who took 6g of green tea extract a day developed mild to moderate gastrointestinal distress, including nausea, vomiting, abdominal pain and diarrhea. The National Center for Complementary and Alternative Medicine says there have also been some reports of liver problems as a result of green tea consumption. Although the evidence is not definitive and the cases are very rare, green tea extract has been associated with liver trouble such as abdominal pain and jaundice.
Tannins
Another possible source of stomach distress from green tea is the tannins it contains. Tannins are one of the polyphenols that occur in tea. Tannins have an astringent taste and can be quite bitter. The Memorial Sloan-Kettering Cancer Center notes that although green tea may have potential to help in the treatment of cancer, adverse effects include nausea and gastrointestinal upset, possibly due to tannins.
References
- Cornell University; Tannins: Fascinating but Sometimes Dangerous Molecules; Antonello Cannas; March 2009
- Memorial Sloan-Kettering Cancer Center; June 2011
- Drugs.com: Green Tea
- Linus Pauling Institute at Oregon State University; Tea; Jane Higdon, Ph.D., et.al.; July 2009
- "Cancer"; A Phase II Trial Of Green Tea In The Treatment Of Patients With Androgen Independent Metastatic Prostate Carcinoma; A. Jatoi, et.al; March 2003
- National Center for Complementary and Alternative Medicine; Green Tea; April 2011
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