Green Tea (Camellia sinensis)

ALSO KNOWN AS: Chinese tea, green tea extract, green tea polyphenols, epigallocatechin gallate (EGCG).

BACKGROUND: Green tea, derived from the leaves of Camellia sinensis, is consumed widely in Asia. Originally cultivated in East Asia, the plant is now grown in the Middle East and in some parts of Africa. Green tea has gained global popularity over the last few decades.

The leaves used to produce green tea are unfermented. They are steamed or heated immediately following harvest. This minimizes oxidation of the polyphenols, which are compounds that act as antioxidants and are thought to confer the health benefits attributed to green tea.

Green tea has been used in traditional medicine as a stimulant, as a diuretic, for wound healing, to promote digestion, and to improve heart health. More recently, green tea and its extracts have been used to prevent and treat hyperlipidemia, hypertension, atherosclerosis, and cancer.

Green tea is available as a dietary supplement in capsule form, as an extract, and in ointments for external application.

RESEARCH: The active constituent of green tea extract is EGCG, which accounts for 40% of its total polyphenol content. Regular consumption of green tea may reduce the risk of hypertension[1] and positively affect mood.[2] It also enhances glucose tolerance in healthy individuals[3] but did not improve insulin sensitivity or glycemic control in those with type 2 diabetes.[4] Green tea also may reduce mortality due to cardiovascular disease in both men and women.[5] Topical application of green tea extracts was shown to be effective against external genital and perianal warts.[6] A green tea extract, sinecatechin, used for genital warts, is an FDAapproved drug.

Several pre-clinical, case-control and prospective cohort studies show that green tea has chemopreventive properties.[7-9] However, a metaanalysis of epidemiologic studies failed to find that green tea prevents stomach cancer.[10] The FDA recently concluded that green tea is unlikely to reduce the risk of breast or prostate cancer.[11] Randomized clinical trials, currently underway, may help resolve the uncertainty surrounding the anticancer potential of green tea.

ADVERSE REACTIONS: Several cases of hepatitis have been associated with consumption of green tea.[12-14] A 40-year-old woman developed pruritic swelling and darkening of the lower lip following use of green tea for several years. Symptoms resolved after she discontinued consumption of green tea. [15] A 38-year-old woman developed thrombotic thrombocytopenic purpura following green tea supplementation for weight loss.[16]

Animal studies indicate that oral consumption of green tea extract while fasting can increase the risk of toxicity.[17]

HERB-DRUG INTERACTIONS: Anticoagulants/ antiplatelets: Theoretically, consumption of large amounts of green tea (0.5–1.0 gallon/day) may provide enough vitamin K to antagonize the effects of anticoagulants and antiplatelet agents, although this effect has not been reported in humans.[18]

Bortezomib (Velcade): EGCG and other polyphenols in green tea can inhibit the therapeutic effect of bortezomib(Drug information on bortezomib) and other boronic acid–based proteasome inhibitors.[19]

Tamoxifen: EGCG was shown to increase the oral bioavailability of tamoxifen(Drug information on tamoxifen).[20]

Verapamil: The bioavailability of verapamil(Drug information on verapamil) increased significantly in the presence of EGCG, an effect thought to be due to P-glycoprotein inhibition by EGCG.[21]

Irinotecan: A study found EGCG to inhibit the transport of irinotecan(Drug information on irinotecan) and its metabolite SN-38 into biliary elimination, resulting in prolongation of their half-life, which can increase toxicity.[22]

Cytochrome P450 3A4 substrates: Green tea extract inhibits CYP3A4 and can affect the intracellular concentration of drugs metabolized by this enzyme.[12]

UGT (uridine 5'-diphospho-glucuronosyltransferase) substrates: Green tea modulates UGT enzymes in vitro and can increase the side effects of drugs metabolized by them.