Tea, Black/Green

Camellia sinensis (L.) Kuntze (syn. C. sinensis L.)

[Fam. Theaceae]

Overview

The use of tea as a beverage in China dates back to at least 2700 B.C.E. (Huang, 1999). Tea continues to be used in the traditional medicine systems of China, Hong Kong, Japan, and Korea (But et al., 1997). Next to water, tea is the most widely consumed beverage in the world (Bushman, 1998; Graham, 1992). International tea production is projected to increase from the 1993–95 average of 1.97 million tons to 2.7 million (UN FAO, 1999). In 1999, the U.S. imported 16,961,460 pounds of green tea, 187,765,660 pounds of black tea, and 7,777,542 pounds of instant tea (USDA, 2000). According to the United Nations Food and Agriculture Organization, there is an increasing body of scientific evidence that both green and black tea can contribute significantly to a healthy lifestyle, and their regular use should be promoted internationally (UN FAO, 1999). Most of the scientific evidence focuses on the cardiovascular and potentially cancer-preventive activity of tea polyphenols and other tea compounds (Gutman and Ryu, 1996; Dufresne and Farnworth, 2001).

Description

Green tea and black tea, although they are derived from the leaves of the same plant Camellia sinensis (L.) Kuntz [Fam. Theaceae], have different concentrations of active constituents. The immediate processing of harvested leaves used for green tea limits enzymatic changes, whereas leaves used for black tea are fermented before preparation, which triggers the enzymatic process. Thus, green tea contains higher concentrations of the active constituents, catechins, compared to black tea.

Green tea is the young leaf of C. sinensis and its cultivated varieties. It is unfermented and subjected to rapid desiccation with applied heat. It contains no less than 2% caffeine (Bruneton, 1999; Ph.Fr.X, 1982–96). It must contain not less than 33% water-soluble extractive on a dry basis, and no less than 4%, or more than 7%, total ash (Health Canada, 1997).

Black tea is the young leaf of C. sinensis and its cultivated varieties, fully fermented, and subjected to rapid desiccation with applied heat. It contains no less than 2.5% caffeine (Bruneton, 1999; Ph.Fr.X, 1982–96), and must contain no less than 25% water-soluble extractive on a dry basis (Health Canada, 1997).

The U.S. Department of Agriculture (USDA) evaluates flavor characteristics of prepared tea using Standard A-2 of the Tea Association of the United States (USDA, 1995). Uniform standards of tea purity, quality, and fitness for consumption are established by the U.S. Secretary of Health and Human Services in accordance with section 3 of the Tea Importation Act (USCS, 1995; 1998). The International Organization for Standardization (ISO) has published standard methods for the classification of grades of tea (ISO, 1997; Willson and Clifford, 1992).

Primary Uses

Cardiovascular

Reduced risk of atherosclerosis (Geleijnse et al., 1999)

Reduced risk of cardiovascular disease (Imai and Nakachi, 1995; Stensvold et al., 1992)

Reduced risk of myocardial infarction (Sesso et al., 1999; Hertog et al., 1993, 1995; Hertog, 1994; Knekt et al., 1996; Stensvold et al., 1992)

Modulation of plasma antioxidant capacity (Leenen et al., 2000; van het Hof et al., 1999; Princen et al., 1998; Ishikawa et al., 1997)

Decreased serum lipid concentration (Kono et al., 1992, 1996)

Other Potential Uses

Oncology

Prevention of colon cancer (August et al., 1999; Ji et al., 1997 )

Reduced incidence of oral mucosal leukoplakia (Li et al., 1999)

Decreased recurrence of Stage I and II breast cancer (Nakachi et al., 1998)

Reduced risk and incidence of pancreatic cancer (Ji et al., 1997)

Reduced risk and incidence of squamous cell lung cancer (Ohno et al., 1995)

Reduced risk and incidence of esophageal cancer (Gao et al., 1994)

Miscellaneous

Symptomatic treatment of mild diarrhea (Bruneton, 1999; But et al., 1997; Meyer-Buchtela, 1999)

Reduced risk of osteoporosis (Hegarty et al., 2000)

Promotes diuresis (Bruneton, 1999; Shih-Chen, 1973)

Digestive aid (Shih-Chen, 1973)

Dysuria; edema (But et al., 1997)

Weight loss (Bruneton, 1999; Wichtl and Bisset, 1994)

Functional asthenia (Bruneton, 1999)

CNS stimulant (Leung and Foster, 1996; Meyer-Buchtela, 1999)

Headache (But et al., 1997; Leung and Foster, 1996)

Dosage

Internal

Crude Preparations

Green tea infusion: 150–250 ml boiling water is poured over 1.0–2.5 g fine cut dried leaf, and steeped 3–5 minutes for use as a stimulant (alkaloids extract rapidly). Steeped at least 10 minutes for use in treatment of diarrhea (catechins take longer to extract). Drunk several times daily (Meyer-Buchtela, 1999). Tea should be steeped for 15–20 minutes to maximize the yield of catechins, though this will make the tea taste bitter (Schulz et al., 1998). At least 1 cup daily for antioxidant effect (Leenen et al., 2000).

Green tea powder: 8 capsules (250 mg each) are taken daily, with meals, to treat obesity (Lecomte, 1985).

Black tea infusion: 150–250 ml boiling water is poured over 2.5 g fine cut, dried leaf, and steeped 2–5 minutes for use as a stimulant (alkaloids extract rapidly). Steeped at least 10 minutes to treat diarrhea (catechins take longer to extract), 2–3 times daily (Meyer-Buchtela, 1999; Wichtl and Bisset, 1994). Drunk 3–4 times daily for protection against atherosclerosis (Geleijnse et al., 1999), 1 or more times daily to reduce risk of myocardial infarction (Sesso et al., 1999).

Standardized Preparations

Dry ethanolic green tea extract: 25% catechins, 2 capsules (250 mg each), 3 times daily with meals for weight control (Dulloo et al., 1999).

Note: Stimulant action of tea is strongest when allowed to steep for 2–5 minutes as caffeine dissolves quickly in hot water. Longer steeping (10–20 minutes) increases the catechin yield, and decreases the stimulant effect because the polyphenols bind the caffeine (Wichtl and Bisset, 1994). Green and black tea catechins are rapidly absorbed, and milk does not impair their bioavailability (Hollman et al., 2001; Leenen et al., 2000; van het Hof et al., 1998). Earlier studies reported that adding milk results in complexation of tea polyphenols by milk proteins, completely inhibiting their antioxidant effects (Serafini et al., 1996).

Duration of Administration

Internal

Most human studies conclude that the regular, long-term, daily use of tea is safe and contributes significantly to prevention (or at least some reduction of incidence) of some serious diseases.

Chemistry

Green Tea

Green tea leaf contains 1–5% xanthine alkaloids (caffeine, theobromine, theophylline, xanthine) (Huang, 1999); 20–30% flavonols; 3–4% flavonols and flavone-glycosides; about 5% phenolic acids; 2–3% proanthocyanidins, 0.59–3.97% free amino acids; and minerals including significant amounts of aluminum, manganese, fluoride, and potassium (Meyer-Buchtela, 1999; Scholz and Bertram, 1995). Tea leaf polyphenols such as catechins, include (+)-catechin (C), (+)-gallocatechin (GC), (–)-epicatechin (EC), (–)-epigallocatechin (EGC), (–)-epicatechin gallate (ECG), and (–)-epigallocatechin gallate (EGCG) (Miketova et al., 1998). Components of prepared green tea infusion, measured in weight percentage of extracted solids include 30–42% catechins, 5–10% flavonols, 2–4% other flavonoids, 7–9% xanthine alkaloids, 6–8% minerals, 4–6% amino acids, 4–6% organic acids, and 1–2% ascorbic acid (Graham, 1992).

Black Tea

Black tea leaf contains polyphenols, such as catechins EGC, EC, EGCG, ECG (Bronner and Beecher, 1998); xanthine alkaloids (2.6–3.5% caffeine, 0.16–0.2% theobromine, 0.02–0.04% theophylline); 1–3% flavanols; 2–3% flavonols and flavone-glycosides; 2–4% phenolic acids; about 2% theaflavine; 6–30% thearubigins; 0.66–2.82% free amino acids; and minerals including significant amounts of aluminum, manganese, fluoride, and potassium (Meyer-Buchtela, 1999; Scholz and Bertram, 1995). After fermentation from green tea to black tea, about 15% of the catechins remain unchanged and the rest convert into theaflavines and thearubigins. The components of prepared black tea infusion measured in weight % of extracted solids include 3–10% catechins, 12–18% thearubigins, 3–6% theaflavines, 6–8% flavonols, 10–12% phenolic acids and depsides, 8–11% xanthine alkaloids, 13–15% amino acids, and about 10% minerals (Graham, 1992).

Pharmacological Actions

Human

Crude Preparations

Black tea: Protects against ischemic heart disease (Geleijnse et al., 1999).

Green tea: Increases plasma antioxidant capacity (Nakagawa et al., 1999); decreases serum concentrations of total cholesterol, triglycerides, and atherogenic index (Imai and Nakachi, 1995); inhibits endogenous formation of nitrosoproline (Xu et al., 1993).

Black and green tea: Increase plasma antioxidant capacity (Leenen et al., 2000); inhibit endogenous formation of nitrosoproline (Wang and Wu, 1991).

Unspecified: Inhibits alpha-amylase activity and lowers pH in digestive tract (Hara, 1997); inhibits endogenous formation of nitrosoproline (Stich, 1992).

Standardized Preparations

Green tea: Activates thermogenesis and fat oxidation (Dulloo et al., 1999).

Unspecified: Reduces fecal moisture, pH, ammonia, and sulfide, and potentially reduces oxidation (Goto et al., 1999).

Animal

Green tea: Inhibits angiogenesis (Cao and Cao, 1999); hypolipidemic (Chan et al., 1999); inhibits unwanted fecal microbes (Isogai et al., 1998); inhibits activity of nitrosamines, polycyclic aromatic hydrocarbons, and heterocyclic amines (Bu-Abbas et al., 1994, 1995); inhibits the formation and growth of solid tumors (Hirose et al., 1994; Mukhtar et al., 1994; Yin et al., 1994); increases the activity of antioxidant and detoxifying enzymes (glutathione reductase, glutathione peroxidase, glutathione S-transferase (GST), catalase, and quinone reductase) in lungs, liver, and small intestine (Khan et al., 1992); has an antimutagenic effect on compounds that induce gastrointestinal epithelial cancers (Yamane et al., 1991); lowers cholesterol (Muramatsu et al., 1986; Yamaguchi et al. 1991).

Black and green tea: Extracts of both green and black tea exhibit cancer chemopreventive action (Heber et al., 1999); are anti-mutagenic and inhibit colon carcinogenesis (Hernaez et al., 1998); inhibit activity of nitrosamines, polycyclic aromatic hydrocarbons, and heterocyclic amines (Weisburger et al., 1994); inhibit formation and growth of solid tumors (Wang et al., 1994).

Unspecified: Inhibits unwanted fecal microbes (Toda et al., 1991). Green tea, but not its isolated catechins, has growth-promoting effects on mammary gland development (Sayama et al., 1996); lowers cholesterol (Chisaka et al., 1988).

In vitro

Green tea: Inhibits enzyme urokinase (Jankun et al., 1997); is antioxidant (Frankel, 1997); inhibits low density lipoprotein (LDL) cholesterol oxidation (Luo et al., 1997); has inhibitory effect on growth of mammary cancer cell lines by inhibiting interaction of estrogen with its receptors (Komori et al., 1993).

Unspecified: Exhibits radical-scavenging activity (Nanjo et al., 1999); inhibits growth of human lung cancer cell line (Fujiki et al., 1998); is antioxidant (Plumb et al., 1999); inhibits enzyme catechol-O-methyl-transferase (COMT) (Borchardt and Huber, 1975).

Mechanism of Action

Anti-carcinogenesis

Tea catechins are absorbed through the oral mucosa, which may assist in preventing oral and esophageal cancers. Levels of EGCG are higher in saliva than in blood after ingestion of a single cup of tea. Drinking tea slowly delivers high concentrations of catechins to the oral cavity and then the esophagus, whereas tea extract in solid dosage forms results in no detectable salivary catechin level (Yang et al., 1999).

Evidence (in vitro) suggests that the synergy of total catechins in whole green tea leaf infusion is more effective as a cancer preventive than isolated EGCG (Suganuma et al., 1999).

The mechanism of green tea’s anti-carcinogenic effects against digestive tract cancers is unclear (Cao and Cao, 1999; Ji et al., 1997).

Green and black teas inhibit human carcinogens possibly due to antioxidative and antiproliferative effects of poly-phenolic fraction (Katiyar, 1992; Yang and Wang, 1993).

Polyphenols may inhibit carcinogenesis by blocking endogenous formation of nitrosamines, polycyclic aromatic hydrocarbons, and heterocyclic amines (Bu-Abbas et al., 1994, 1995; Weisburger et al., 1994).

Green and black tea have comparable antioxidant effects that may diminish the formation of oxidized metabolites of DNA, with an associated lower risk of cancers (Weisburger, 1999).

Green tea may alter gut flora. Its effects on reduction of dysbiosis suggest a mechanism for prevention of colon cancer (Yarnell, 1999).

Tea catechins inhibit alpha-amylase activity in the small intestine, and some are absorbed into the portal vein. By lowering the pH in the digestive tract, tea catechins decrease putrefactive products and increase organic acids (Hara, 1997).

Antioxidant

Green and black tea have comparable antioxidant effects that may play a role in lowering the oxidation of LDL cholesterol, with a consequent decreased risk of heart disease (Weisburger, 1999).

Flavonoids in green or black tea may reduce the risk of myocardial infarction by inhibiting the oxidation of LDL cholesterol (Rimm et al., 1996; van het Hof et al., 1999), reducing platelet aggregation (Ho et al., 1992), or reducing ischemic damage (Laughton et al., 1991).

Green tea contributes to the prevention of cardiovascular disease by increasing the antioxidant capacity of plasma (Nakagawa et al., 1999).

Proposed mechanisms of tea flavonoid antioxidant activity include its hydrogen-donating ability, delocalization of electrons, and metal ion chelation. Tea beverage has greater in vitro antioxidant capacity than most fruits and vegetables per serving and is more potent than vitamins C and E and the carotenoids. Tea and its flavonoids protect LDL cholesterol from oxidation following co-incubation in vitro (Najemnik et al., 1999).

Central nervous system stimulant

Tea contains water-soluble xanthine alkaloids such as caffeine, which stimulate the central nervous system and adrenal glands, increasing synthesis and release of specific neurotransmitters and hormones. Caffeine increases secretion of the neurotransmitter norepinephrine and the adrenal hormone epinephrine, while blocking central adenosine receptors (Gawin, 1988; Gilman et al., 1985).

Thermogenesis

By inhibiting catechol O-methyltransferase (COMT), the enzyme that degrades norepinephrine, tea catechins prolong the life of norepinephrine in the synaptic cleft, while tea alkaloids inhibit phosphodiesterases, which prolongs the life of cAMP in the cell, resulting in an increased, and more sustained effect, of norepinephrine on thermogenesis (Dulloo et al., 1999).

Epigallocatechin gallate (EGCG) can attenuate peroxide production in glial cells by either inhibiting the deamination of monoamines or acting as a free radical scavenger, thereby reducing oxidative neuronal damage associated with various neurodegenerative diseases (Mazzio, 1998).

Contraindications

None known (Meyer-Buchtela, 1999). Persons with weakened cardiovascular systems, renal diseases, thyroid hyperfunction, elevated susceptibility to spasm, and certain psychic disorders (e.g., panicky states of anxiety) should use tea with caution (Fleming et al., 2000).

Pregnancy and Lactation: No known restrictions during pregnancy or lactation (McGuffin et al., 1997), though pregnant women should typically not ingest more than five cups daily (about 300 mg caffeine daily) and ingestion of tea while nursing may cause sleep disorders in some infants (Fleming et al., 2000).

Adverse Effects

Side effects of nervous system stimulants may include nervousness, anxiety, heart irregularities, headaches, tremors, hypertension, restlessness, insomnia, daytime irritability, irritation of the gastric mucosa, and diuresis (McGuffin et al., 1997). These effects are generally for high dosages of caffeine-containing herbs and are not associated with the ingestion of reasonable amounts of tea (e.g., 1–10 cups per day).

Drug Interactions

Xanthine (e.g., caffeine, theophylline) derivatives from black tea can diminish effects of coronary vasodilator drugs such as dipyridamole and should not be taken concurrently (Morant and Ruppanner, 2001). Green tea has a possible synergistic effect when taken with sulindac and/or tamoxifen and may reduce their adverse effects (Suganuma et al., 1999). Green tea is a source of vitamin K; one case report suggests that green tea is a probable antagonist of warfarin (Taylor and Wilt, 1999). Herbs high in tannins may impair absorption of theophylline, a bronchodilator drug used to treat asthmatics (Austin, 1999; Brinker, 2001). Tea tannins can also interfere with intestinal absorption of nutrients and vitamins (Huang, 1999). In infants, tannins can bind iron and reduce its absorption, contributing to the development of microcytic anemia (Merhav, 1985). Resorption of alkaline medications can be delayed due to chemical bonding with tea tannins (Fleming et al., 2000). In vitro, black tea constituents can cause precipitation of amitriptyline, fluphenazine, haloperidol, and Imipramine (Lasswell et al., 1984; Kulhanek, 1981). Large amounts of caffeine may increase activity and side effects of theophylline. Limiting intake of caffeine-containing beverages to small amounts will avoid this potential interaction (Austin, 1999; Threlkeld, 1991), and those associated with numerous other drugs affected by caffeine consumption (Brinker, 2001).

American Herbal Products Association (AHPA) Safety Rating

Class 2d: Black teas are not recommended for excessive or long-term use (McGuffin et al., 1997). (Editors’ note: It is unclear why AHPA has given a Class 2d safety rating to black tea and not to green tea. Both black and green tea are, in fact, recommended for long-term use for health benefits.)

Regulatory Status

Belgium: Permitted as a traditional herbal diuretic (De Smet et al., 1993).

Canada: Food (Health Canada, 1997). Substantiated health claims will be permitted with premarket authorization after Natural Health Product (NHP) regulations become final in 2001 or 2002.

France: Traditional Herbal Medicine listed in Annex I of the 1998 French Explanatory Note with four approved oral use indications and two topical use indications. Green and black tea are official in the French Pharmacopoeia, Ph.Fr. X (Bruneton, 1999).

Germany: Food. Not reviewed by the German Commission E. No monograph in the German Pharmacopoeia.

Italy: Food.

Sweden: Classified as a foodstuff and natural product (De Smet et al., 1993). No products containing tea leaf are presently registered in the Medical Products Agency’s (MPA) “Authorized Natural Remedies,” “Homeopathic Remedies” or “Drugs” listings (MPA, 2001).

Switzerland: One multiple-ingredient digestive aid instant tea (Drosana^® Verdauungs und Magentee) containing tea leaf dry extract is listed in the Swiss Codex 2000/01 (Ruppanner and Schaefer, 2000). No monograph in the Swiss Pharmacopoeia.

U.K.: Food. Not entered in the General Sale List (GSL). No monograph in the British Pharmacopoeia.

U.S.: Generally Recognized as Safe (GRAS) (US FDA, 1998). Dietary supplement or food depending on label claim statement (USC, 1994). No monograph in the USP-NF.

Clinical Review

Twenty-nine studies are outlined in the following table, “Clinical Studies on Tea Leaf,” including a total of 68,242 subjects. All but three of these studies (Princen et al., 1998; Nakachi et al., 1998; Hartman et al., 1998) demonstrated positive effects for indications in the areas of cardiovascular health, cancer, osteoporosis, obesity, and bowel conditions. Most of the studies are large-population epidemiological studies on the influence of black and/or green tea consumption on disease prevention. The table includes 15 cardiovascular studies investigating a range of potential applications, including two cross-over studies on plasma antioxidant activity (Leenen et al., 2000; van het Hof et al., 1999); a randomized, placebo-controlled (R, PC) study on energy expenditure and fat oxidation (Dulloo et al., 1999); a PC study on tea’s protective effect against ischemic heart disease (Geleijnse et al., 1999); a multi-center, case-controlled (MC, CC) study on tea’s protective effect against myocardial infarction (Sesso et al., 1999); and tea’s effects on serum lipid concentrations and resistance of LDL cholesterol to oxidation (Ishikawa et al., 1997; Kono et al., 1992, 1996; van het Hof et al., 1997). At least 13 large-population, CC cancer studies have been published. Five recent CC cancer studies listed in the table evaluated the consumption of tea and its protective effect against development of pancreatic and colorectal cancers (Ji et al., 1997); various cancers (Imai et al., 1997); stomach cancer (Yu et al., 1995); lung cancer (Ohno et al., 1995); and esophageal cancer (Gao et al., 1994). Other studies investigated tea’s use in protecting older women against osteoporosis (Hegerty et al., 2000), and tea’s effect on fecal flora in nursing home residents (Goto et al., 1998, 1999). One DB, PC study investigated tea’s use in the treatment of severe obesity and found significant weight loss after 30 days (Lecomte, 1985). A recent meta-analysis examined the effect of tea on stroke, myocardial infarction, and all coronary heart disease. The estimated effects of tea on stroke and coronary heart disease were too heterogeneous to assess. The study found an estimated 11% decrease in the incidence rate of myocardial infarction (fixed-effects relative risk estimate = 0.89, 95% confidence interval: 0.79, 1.01).

Branded Products

Arkocaps/Phytotrim^®: Arkopharma Laboratories / BP 28-06511 / Carros Cedex / France / Tel: +33-49-32-91-128 / Email: info@arkopharma.com. Capsules contain 250 mg powdered green tea leaf.

Exolise^®: Arkopharma Laboratories. Capsules contain 250 mg alcoholic green tea leaf dry extract standardized to 25% (250 mg/g) total catechins and 10% (100 mg/g) caffeine.

Lipton “Brisk” Tea^® (black tea): Unilever Bestfoods North America / 800 Sylvan Ave. / Englewood Cliffs, NJ 07632 / U.S.A. / Tel: (800) 697-7887 / (888) LIPTON-T / Email: letters.liptontusa@unilever.com / www.liptont.com. 2.21 g tea leaf per single serve bag providing 46.9 mg total catechins (8.6 mg epicatechin, 14.2 mg epicatechin gallate, 7.0 mg epigallocatechin, 17.1 mg epigallocatechin gallate), 11.9 mg total theafavines, 10.7 mg flavonols, 151.2 mg thearubigins and 220.7 mg total polyphenols.

Lipton^® Green Tea: Unilever Bestfoods North America. 2.27 g tea leaf per single serve bag providing 186.3 mg total catechins (26.7 mg epicatechin, 30.3 mg epicatechin gallate, 50.6 mg epigallocatechin, 78.7 mg epigallocatechin gallate), 0.2 mg total theafavines, 12.0 mg flavonols, and 198.5 mg total polyphenols.

Twinings^®Darjeeling Tea (black): Twinings London / 216 The Strand / London / U.K. / www.twinings.com. Each dose of 2.2 g leaf provides 7.6 mg epicatechin, 20.2 mg epigallocatechin, 43 mg epigallocatechin gallate, 2.2 mg theaflavin, 1.4 mg theaflavin monogallate, and 0.8 mg theaflavin digallate.

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