Green Tea

Scientific names: Camellia sinensis (L.) Kuntze. Family: Theaceae

Common names: Green tea also is known as tea, black tea, oolong tea, Veregen.

Efficacy-safety rating:

ÒÒ...Ethno or other evidence of efficacy.

Safety rating:

...Little exposure or very minor concerns.

What is Green Tea?

Black, oolong, and green tea are produced from the leaves of C. sinensis, which is native to eastern Asia but also grown in other areas. This evergreen shrub or tree grows to over 9 m in height and is pruned from 60 cm to 1.5 m for cultivation. Its dark green, serrated-edged leaves are alternate and oval, while its white and fragrant blossoms appear singly or in clusters. Green tea consists of dried leaves, while black tea is produced by a complex wilting and fermentation process. Oolong tea is produced by a process intermediate to that of green and black tea.

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What is it used for?

Traditional and ethnobotanical uses

The dried, cured leaves of C. sinensis have been used medicinally for more than 5,000 years. Traditional Chinese medicine has recommended drinking green tea for the prevention of ill health, which in Asia is still regarded as a healthy practice.

General uses

Tea is traditionally consumed as a beverage. Evidence from clinical trials suggests that green tea plays a role in metabolic syndrome because it may have an impact on body weight, glucose homeostasis, and other cardiovascular risk factors. It has yet to be determined whether green tea can help prevent cancer; however, a role in the prevention of stroke has been suggested. Topical applications have been studied for protection from ultraviolet damage, and a commercial preparation has been approved for use in the treatment of anogenital warts.

What is the recommended dosage?

A daily intake of 3 to 5 cups/day (1,200 mL) of green tea will provide at least 250 mg/day of catechins. Green tea extract should not be taken on an empty stomach due to the potential for liver toxicity from excessive levels of epigallocatechin gallate. Anogenital warts: topical application of sinecatechins 3 times a day for a maximum of 6 weeks. Cardiovascular effect: 400 to 716 mg/day of catechins have been used in trials in divided dosages. Diabetes: Dosages of epigallocatechin gallate range from 84 to 386 mg/day in trials evaluating glucose homeostasis. Obesity: Dosage ranges used in trials include 270 to 800 mg/day of epigallocatechin gallate, or 125 to 625 mg/day of catechins.

How safe is it?

Contraindications

Contraindications have not been identified; however, use caution when liver failure is present.

Pregnancy/nursing

The US Food and Drug Administration advises those who are or may become pregnant to avoid caffeine.

Interactions

Vitamin K present in green tea may affect the blood thinning effects of warfarin. Green tea consumption reduces the bioavailability of folic acid and may interfere with the absorption of iron.

Side Effects

There are no reports of clinical toxicity from daily tea consumption as a beverage. Adverse events include headache, dizziness, and GI symptoms. Liver toxicity, including 1 fatality, has been associated with high plasma levels of epigallocatechin gallate or its metabolites.

Toxicities

Multidose studies suggest that a daily dose of 800 mg/day of epigallocatechin gallate capsules for up to 4 weeks is safe and well tolerated. High-dose oral green tea extract and catechins were toxic to rat livers.

References

  1. Green Tea. Review of Natural Products. Facts & Comparison Online. May 2010. Accessed April 20, 2010.

Copyright © 2009 Wolters Kluwer Health

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