Written by Jianping Liu, Xun Li and the CAM-Cancer Consortium.
Updated February 13, 2014

Green tea (Camellia sinensis)

What is it?

Scientific names 

Green tea is derived from Camellia sinensis, an evergreen shrub of the Theaceae family, which grows mainly in parts of Asia, the Middle East and Africa. It comes from the same plant as black tea but it is produced in a non-fermenting process thus is believed to be the strongest tea with the least loss of herbal elements. According to the fermentation degree and plants sources, there are classifications as green tea, white tea, yellow tea, black tea and dark tea. With increasing fermentation, the number of bioactive elements decreases.

Ingredients 

Green tea contains antioxidants. The main active ingredients identified in green tea include polyphenolic compounds such as epicatechin (EC), epicatechin-3-gallate (ECG), epigallocatechin (EGC), and epigallocatechin-3-gallate (EGCG), which are thought to be responsible for their anti-carcinogenic and anti-mutagenic activity. Other polyphenols in green tea include flavanols and their glycosides and depsides such as cholorogenic acid, quinic acids, carotenoids, trigalloylglucose, lignin, protein, chlorophyll, minerals (depending on the soil content, aluminum and manganese), caffeine, and very small amount of methylxanthines. 

Application and dosage 

Green tea can be consumed as a brewed beverage or as dietary supplements in form of liquids, capsules, or tablets containing green tea extract. Commercial products, or green tea for medicinal use, are provided by tea manufacturers or different pharmaceutical herbal medicine companies. Water for green tea should be around 80 to 85 °C; the higher the quality of the leaves, the lower the temperature; high-quality green teas can have new water added as many as five times. Currently, there is no established recommended dose for green tea extract. For cancer prevention, studies have examined the effects of habitually drinking between one to ten cups per day, although these findings require confirmation. 

History/providers 

Green tea consumption began in China with legendary origins of more than 4,000 years ago. A legend suggests it was an Emperor called Shen Nung who accidentally discovered tea. Then green tea has an origin linked to the highest tier of Chinese society, which made it expensive and only accessible to the rich. It was not until the 14th century that green tea become widespread throughout China. It has been used for its taste and medicinal qualities in most of Asia. In the 16th century, green tea was introduced to Europe and the USA.1 

The Kissa Yojoki (Book of Tea), written by Zen priest Eisai in 1191, describes how drinking green tea can have a positive effect on the five vital organs and discusses tea's medicinal qualities.2 

Claims of efficacy/alleged indications 

A variety of health benefits have been suggested including cancer prevention, reduced risk for cardiovascular disease, increased bone density, fat loss promotion and protection against neurodegenerative disease. 

Mechanism of action 

Human studies on the pharmacokinetics of green tea polyphenols have been conducted. Polyphenols from green tea have been shown to be powerful antioxidants with anticarcinogenic properties. EGCG, the most abundant and biologically active polyphenol in green tea, induces apoptosis and suppresses proliferation of cancer cells by modulating multiple signal transduction pathways. EGCG can also covalently bind to cysteine residues in proteins through autoxidation and subsequently modulate protein function.3 Studies have shown that tea catechins inhibit hepatocyte growth factor receptor (MET kinase) activity in human colon cancer cells. 

Prevalence of use 

Tea is the most popular beverage next to water around the world, and green tea accounts for 20% of tea consumption. It is particularly popular in China, Japan, and other South-East Asian countries. 

Legal issues 

Green tea is sold as beverage or dietary supplement. It therefore does not need to be approved by the FDA or EMA (European Medicines Agency), but no medicinal claims associated with green tea can be made. 

Cost and expenditure 

The cost of green tea differs substantially due to variable growing conditions, horticulture, production processing and harvesting time. Therefore, on the Internet in China, prices for green tea generally range from 2.67 Euros/3.63 USD per 500g to 284.82 Euros/388.22 USD per 500g in bulk. The price of green tea in the USA and Europe is about 12.46 Euros/17 USD per 500 mg 100 caps.

Citation Jianping Liu, Xun Li , CAM-Cancer Consortium. Green tea (Camellia sinensis) [online document]. http://ws.cam-cancer.org/The-Summaries/Herbal-products/Green-tea-Camellia-sinensis. February 13, 2014.

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