Green Tea

Plant Part Used

Leaf.

Active Constituents

Flavonoid derivatives (polyphenols) including (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG); also contains the alkaloids caffeine (3,810 - 93,000 ppm in leaf), theophylline, theobromine.(1)

[span class=alert]This section is a list of chemical entities identified in this dietary supplement to possess pharmacological activity. This list does not imply that other, yet unidentified, constituents do not influence the pharmacological activity of this dietary supplement nor does it imply that any one constituent possesses greater influence on the overall pharmacological effect of this dietary supplement.[/span]

Introduction

Green tea is an evergreen shrub that has long been used in much of the world as a popular beverage and a respected medicinal agent.(2) An early Chinese Materia Medica lists green tea as an agent to promote digestion, improve mental faculties, decrease flatulence and regulate body temperature. The earliest known record of consumption is around 2700 B.C. Ceremonies, celebrations, relaxation time and ordinary meals usually consist of tea in most parts of the world, except the United States, where coffee has become the most popular beverage. Unlike black tea (also Camellia sinensis) which is produced by oxidizing the young tea leaves, green tea is produced from steaming fresh leaves at high temperatures, thereby inactivating the oxidizing enzymes and leaving the polyphenol content intact.

Green tea is an antioxidant and is used in promoting cardiovascular health(3),(4) and reducing serum cholesterol levels in laboratory animals and humans.(5),(6),(7) Studies suggest that green tea contains dietary factors that help decrease the development of some infectious diseases and dental caries.(8),(9),(10) Green tea has diuretic, stimulant, astringent, antibacterial, antifungal, anticarcinogenic, thermogenic and anti-inflammatory properties.(11) Green tea has also been reported to enhance immunity.(12)

Interactions and Depletions

Interactions

If using a green tea supplement that contains caffeine, there may be interactions with several medications including:

Dosage Info

Dosage Range

250-500mg (standardized extract) daily.

Tea: 1 to 6 cups daily using 5gm (one teaspoonful) of dried leaf per cup.(13)

Most Common Dosage

500mg (standardized extract) daily.

Tea: 3 cups daily using 5gm (one teaspoonful) of dried leaf per cup.

Standardization

[span class=doc]Standardization represents the complete body of information and controls that serve to enhance the batch to batch consistency of a botanical product, including but not limited to the presence of a marker compound at a defined level or within a defined range.[/span]

The most current available medical and scientific literature indicates that this dietary supplement should be standardized to 90% polyphenols, containing at least 40-75% (-) epigallocatechin-3-gallate (EGCG). Caffeine-free products are recommended, unless the supplement is being used in weight loss management. The caffeine containing green tea is preferred.

Uses

Frequently Reported Uses

  • Antioxidant
  • Anti-Aging
  • Cancer Prevention And Support
  • Atherosclerosis/Cholesterol Health
  • Metabolic syndrome
  • Cardiovascular Health
  • Immune Enhancement
  • Thermogenesis/Weight Loss

Other Reported Uses

  • Anti-inflammatory
  • Insulin regulation
  • Antibacterial
  • Antifungal
  • Chemotherapy Enhancing Effects
  • Decreases Platelet Aggregation, Improves Blood Flow
  • Chemotherapy And Radiation Protection
  • Dental Caries
  • Immune Enhancement
  • Mild Diuretic
  • Bone health

Toxicities & Precautions

General

Green tea is reported safe in recommended dosages. No known toxicity or adverse effects even under high doses.(11)

As tea contains caffeine, use with coffee or other caffeinated beverage is not recommended; caffeine-free products are available. Consumption of caffeinated green tea has been reported to increase blood pressure, although not in a clinically significant amount.(14)

Health Conditions

If the product is not decaffeinated, use with caution in individuals with peptic ulcer and cardiovascular disease.

Based on pharmacology, use with caution in individuals with bleeding disorders.

Use green tea extracts with caution in individuals with impaired liver function. Hepatotoxicity has been reported in 7 case reports where green tea was a probable cause.(82),(83) However, a placebo-controlled study using high polyphenol green tea extract showed no impairment of liver function.(84)

Side Effects

If the product is not decaffeinated, it may cause insomnia, decreased appetite, tachycardia or nervousness in sensitive individuals. Consumption of caffeinated green tea has also been reported to increase blood pressure, although not in a clinically significant amount.(14)

Pregnancy/ Breast Feeding

To date, the medical literature has not reported any adverse effects related to fetal development during pregnancy or to infants who are breast-fed. Yet little is known about the use of this dietary supplement while pregnant or breast-feeding. Use with caution.

Age Limitations

To date, the medical literature has not reported any adverse effects specifically related to the use of this dietary supplement in children. Since young children may have undiagnosed allergies or medical conditions, this dietary supplement should be used with caution following proper evaluation.

Pharmacology

Antioxidant

Green tea is reported to have antioxidant properties.(15),(16) and the ability to protect against oxidative damage of red blood cells.(17),(18) Most of green tea’s therapeutic uses in humans are associated with its antioxidant activity. Antioxidants protect cells and tissues against free radical oxidative damage and injury.(19) Green tea’s antioxidant effects seem to be dependent upon the polyphenol (catechin) fraction.(20),(21) The antioxidative action of the green tea polyphenols includes inhibiting lipid peroxidation, iNOS and the production of inflammatory cytokines along with reducing the alpha-tocopheroxyl radical to regenerate alpha-tocopherol.(22),(85) (-)-epigallocatechin gallate (EGCG), isolated from green tea, displays antioxidant properties in vitro and is thought to act as an antioxidant in humans and be responsible for much of green tea’s therapeutic effects.(23),(86)

One cup of green tea of usual strength (1-2%) can provide the same potential for improving antioxidant status as around 150 mg of pure ascorbic acid (vitamin C).(24) One study reported that the addition of milk to any tea may significantly lower the antioxidant potential.(25) However, other studies have reported that milk added to green tea does not effect the antioxidant capacity in humans.(26),(27) It is recommended to use fat-free milk when adding to tea beverages to preserve the antioxidant value.(28)

A clinical study on the antioxidant capacity of green tea catechins was conducted.(29) Eighteen healthy male volunteers were administered an oral green tea extract (254 mg of total catechins per individual). One hour after administration, plasma was drawn and tested for its antioxidant capacity. The individuals that ingested the green tea had significantly lower phosphatidylcholine hydroperoxide levels correlating inversely with an increase in plasma green tea constituent (ECGC) levels - indicating a rise in the antioxidant capacity of these treated subjects.

Another clinical study investigated the antioxidant effect of green tea ingestion in 10 healthy individuals (5 women, 5 men, ages 23-25).(30) The results were that 150ml of green tea did not significantly increase the antioxidant capacity of plasma, but after ingesting 300ml, the total antioxidant capacity of plasma had increased significantly, having an antioxidant capacity of 7.0% after 60 min and 6.2% after 120 min. Also, after ingesting the 450ml of tea, the antioxidant capacity of the plasma increased 12.0% after 60 min and 12.7% after 120 min over the baseline value.

Cigarette smoking is one of the major causes of death in the United States.(31) A study compared the chemopreventive effects of green tea and coffee in cigarette smokers.(32) Results showed that the frequencies of sister-chromatid exchange (SCE) in mitogen-stimulated peripheral lymphocytes from smokers was elevated (9.46 +/- 0.46) vs. non-smokers (7.03 +/- 0.33); however, the frequency of SCE in smokers who consumed green tea (7.94 +/- 0.31) was comparable to that of non-smokers, with the authors concluding that green tea can block the cigarette-induced increase in SCE frequency. Coffee did not exhibit a significant inhibitory effect on smoking-induced SCE. Another human study confirms the decrease in oxidative DNA damage caused by cigarette smoking when green tea is consumed.(33) Green tea topically in sunscreens have also been reported to : have potential photoprotective effects on UVR-induced photoaging and photoimmunosuppression based on the antioxidant properties.(87)  Another 2 year, double-blind, randomized placebo-controlled trial found that use of green tea polyphenols topically did not improve histological photoaging parameters in human subjects.(88)

Cardiovascular Protection

Positive benefits on the cardiovascular system, particularly blood lipid levels, have been reported with the use of green tea in human subjects.(3),(89) Green tea was reported to lower cholesterol levels by blocking the lipid peroxidation of LDL.(34),(35) Consumption of green tea has been associated with decreased serum concentrations of total lipids and triglycerides, an increase in HDL cholesterol, together with a decreased proportion of LDL and VLDL.(36) Also, an increased resistance of LDL to in vivo oxidation has been reported.(37) In two studies, consumption of green tea as a beverage did not show any benefit in reducing serum cholesterol, but the positive effects are reported from other studies.(38),(39) Mechanisms of green tea’s lipid lowering activity also include fatty acid synthase gene suppression by tea polyphenols (EGCG, theaflavins) which leads to down-regulation of EGFR/PI3K/Akt/Sp-1 signal transduction pathways.(90)

Use of a standardized green tea product may significantly increase the benefits of decreasing LDL oxidation. One in vitro study reported the addition of catechins from green tea had a gradual regenerative effect on alpha-tocopherol in human LDL.(40) Green tea has also been reported to be an inhibitor of thromboxane formation and platelet aggregation, of importance in the prevention of atherosclerosis.(41),(42)

A randomized, double-blind, placebo-controlled, parallel study using green tea in 111 healthy adult volunteers 21-70 y old was performed. After 3 weeks, the green tea was effective for decreasing systolic and diastolic blood pressure, blood pressure, LDL cholesterol, oxidative stress, and markers of chronic inflammation, all independent cardiovascular risk factors.(91)

 

Anticarcinogenic Activity

Green tea may have a preventative effect against cancer.(92) Green tea polyphenols are powerful antioxidants and have been reported to protect in varying degrees to be effective against certain cancers, including colon, endometrial, rectal, bladder,(43) breast,(44) stomach, pancreatic, lung, esophageal and prostate.(45),(46),(47),(48),(93) Further research in the area of green tea consumption and use of standardized extracts in cancer is warranted.

The inhibitory effects of green tea on Carcinogenesis have been investigated in laboratory studies using (-)epigallocatechin gallate (EGCG) or crude green tea extract.(49) Further, EGCG has been reported to inhibit the growth of cancer cells, lung metastasis in an animal model and urokinase activity.(50),(51) Investigators have reported that increased consumption of green tea was associated with decreased numbers of axillary lymph node metastases among pre-menopausal women with stage I and II breast cancer and with increased expression of progesterone and estrogen receptors among postmenopausal women.(52),(53) Claims have been made that increased consumption of green tea prior to clinical cancer onset may be associated with improved prognosis of stage I and II breast cancer. This association may be related to a modifying effect of green tea on the clinical characteristics of the cancer.(54)

As stated, green tea and its major polyphenolics have been studied to determine if they prevent chemically induced tumors in a variety of experimental animal models.(55),(56) The exact mechanism(s) of the anticarcinogenic activity remains to be found, but green tea polyphenolics are reported to:(10)

  • Enhance antioxidant (glutathione peroxidase, catalase and quinone reductase) and phase II (glutathione-S-transferase) enzyme activities
  • Inhibit chemically induced lipid peroxidation
  • Inhibit irradiation- and TPA-induced epidermal ornithine decarboxylase (ODC) and cyclo-oxygenase activities
  • Inhibit protein kinase C and cellular proliferation
  • Have anti-inflammatory activity
  • Enhance gap junction intercellular communication

A review of studies from 1996-2008 found that consuming 2 cups/day of green tea was associated with an 18% decrease risk of developing lung cancer.(94) A 2006 meta-analysis of epidemiological studies found green tea consumption was correlated with a decreased risk for breast cancer.(95)  A 2009 meta-analysis found that green tea consumption (2 cups/day) decreases the risk of endometrial cancer.(96)  A Cochrane Database System Review in 2009 found that evidence of green tea consumption and decreased cancer risks is limited and more studies need to be performed, especially using standardized extracts.(97)

Literature suggests that carcinogenic substances, termed heterocyclic amines, can be found in cooked foods such as meats (especially when broiled or grilled), greatly increasing the risks of colon cancer.(57) In vitro and laboratory animal experiments have reported that the polyphenols in green tea may inhibit the formation and destructive capabilities of these heterocyclic amines.(58),(59)

Chemotherapy Enhancement and Radiation Protection

The oral administration of green tea reportedly enhanced the inhibitory effects of doxorubicin on tumor growth.(60),(61) The doxorubicin concentration in the tumor was increased by the combination of green tea with doxorubicin. In contrast, the increase in doxorubicin concentration was not observed in normal tissues after green tea combination.(62) Green tea has also been reported to increase the tumor inhibiting effects of Adriamycin (doxorubicin).(63),(64)

There have also been several animal studies that support the use of green tea in the prevention of UVR-induced skin Carcinogenesis and as a topical skin protectant against UV radiation.(65),(66),(67),(68) In vitro studies on human skin have reported similar results.(69) A recent human study reported that a topical application of EGCG from green tea prior to exposure to UV radiation had preventative effects on damage to the skin.(70) A single UV exposure of 4x MED to human skin was found to increase catalase activity (109-145%) and decrease glutathione peroxidase (GPx) activity (36-54%) and total glutathione (GSH) level (13-36%) at different time points studied. Pretreatment of the skin with EGCG from green tea was found to restore the UV-induced decrease in GSH level and protection of the skin to the antioxidant enzyme GPx. Further studies are warranted to elucidate the preventive effects of EGCG against multiple exposures to UV light on human skin.

Arthritis/Anti-inflammatory

An antioxidant-rich polyphenolic fraction isolated from green tea has been reported to possess anti-inflammatory properties in laboratory animals. One laboratory animal study reported positive benefits on collagen-induced arthritis in mice.(71) The mice exhibited a significant reduction in the incidence of arthritis (33% to 50%) as compared with mice not given green tea polyphenols. Analysis showed a marked reduction in the expression of inflammatory mediators such as cyclooxygenase 2, IFN-gamma, and tumor necrosis factor alpha in arthritic joints of green tea polyphenol fed mice. Additionally, total IgG and type II collagen-specific IgG levels were lower in serum and arthritic joints of the treated mice. The authors concluded that a polyphenolic fraction from green tea may be useful in the prevention of onset and severity of arthritis.

An interesting study of 1256 women in the UK aged 65-76 (1134 tea drinkers and 122 non-tea drinkers) reported that the tea drinkers had significantly greater mean bone mineral density measurements (approximately 5%, adjusted for age and body mass index), independent of smoking status, the use of hormone replacement therapy, coffee drinking, and whether milk was added to tea.(72) The authors concluded that older women who drank tea had higher bone mineral density measurements than did those who did not drink tea, and drinking tea may help in the fight for protection against osteoporosis in older women. However, an animal study has reported that tannins contained in teas (black and green) may decrease the absorption of calcium and iron to some extent.(72) In the study, green tea also decreased the absorption rate of zinc while black tea reportedly increased the rate. Both teas promoted the absorption of manganese and copper.

Clinical studies suggest green tea consumption may decrease the risk of fracture by improving bone mineral density and supporting osteoblastic activities while suppressing osteoclastic activities.(98)

Anticariogenic

Human and laboratory studies have supported the use of green tea as a preventative measure in dental caries.(74),(75),(76) Salivary amylase hydrolyzes food starch to low molecular weight carbohydrates (maltose) that are easily fermentable. A recent study reported that consumption of tea (black or green) inhibit the release of maltose up to 70%.(77) Black tea was more potent of an inhibitor than green tea. Another study reported that a green tea extract was effective in reducing the gingival inflammation caused by periodontal structures such as dentures.(78)

A Phase II randomized, placebo-controlled trial found green tea extract to be useful in suppressing oral premalignant lesions in patients at high risk, in part through reducing angiogenic stimulus (stromal VEGF).(99)

Metabolic Health

An increasing number of human studies have found that consumption of green tea catechins has a positive effect on the major Metabolic Syndrome conditions such as obesity, type-2 diabetes and cardiovascular risk factors.(100),(101)

A double-blind controlled study found that using green tea extract in patients with type 2 diabetes who were not on insulin resulted in a more significant decrease in waist circumference along with increasing adiponectin levels.(102) The authors concluded that green tea in the prevention of obesity aids in the recovery of Ins-secretory ability and helps maintain low hemoglobin A(1c) levels in type 2 diabetic patients who do not yet require insulin therapy. A small counter-balanced crossover study in healthy male subjects found that acute green tea extract ingestion can increase fat oxidation during moderate-intensity exercise and can improve insulin sensitivity and glucose tolerance.(103) Another small clinical study found that green tea consumption lowered hemoglobin A1c levels in individuals with borderline type 2 diabetes.(104) Another clinical study found no change in glycemic control after 3 months of supplementation with green tea extract in adults with type 2 diabetes.(105)

Weight Control/ Thermogenic Activity

Literature suggests that green tea and combinations including tyrosine, caffeine and other supplements may be beneficial in weight control,(106) although there are negative reports.(107) Studies on green tea's thermogenic properties have demonstrated a synergistic interaction between caffeine and catechin polyphenols that appears to prolong sympathetic stimulation of thermogenesis.(108) Laboratory studies with adipocyte cell lines and animal models have demonstrated that EGCG inhibits extracellular signal-related kinases (ERK), activates AMP-activated protein kinase (AMPK), modulates adipocyte marker proteins, and down-regulates lipogenic enzymes as well as other potential targets in obesity and weight loss.(109)

A randomized, placebo-controlled study of 10 individuals was conducted to investigate whether a green tea extract could increase the 24-h energy expenditure and fat oxidation in humans.(80) Compared to the placebo, the green tea extract resulted in a significant increase in 24-h energy expenditure (4%; P < 0.01) and a significant decrease in 24-h respiratory quotient without a change in urinary nitrogen. Twenty-four-hour urinary excretion of norepinephrine was higher during treatment with the green tea extract than with the placebo. Treatment with caffeine alone in amounts equivalent to those found in the green tea extract had no effect on energy expenditure and respiratory quotient nor on urinary nitrogen or catecholamine excretion. The authors concluded that green tea has thermogenic properties and promotes fat oxidation beyond that explained by its caffeine content, with the green tea extract having a role in the control of body composition via sympathetic activation of thermogenesis, fat oxidation, or both. Another clinical study reported similar results, that green tea extract may stimulate brown adipose tissue thermogenesis to an extent which is much greater than can be attributed to its caffeine content, with thermogenic properties residing primarily in an interaction between its high content in catechin-polyphenols and caffeine with sympathetically released noradrenaline (NA).(81)

A randomized, placebo-controlled, double-blind parallel trial was conducted in 80 overweight and moderately obese subjects to compare weight loss using green tea + caffeine or placebo, both in addition to an adequate protein (AP) diet (50-60 g protein/d) or an HP diet (100-120 g protein/d).(110)  The green tea-caffeine mixture, as well as the HP diet, improved weight loss independently through thermogenesis, fat oxidation, sparing FFM, and, for the HP diet, satiety; a possible synergistic effect failed to appear. Another double-blind parallel multicenter study found that green tea polyphenols given to 240 patients led to a reduction in body fat, systolic blood pressure, and LDL cholesterol.(111)

Other Uses

Green tea consumption may be beneficial in reducing the effects of environmental intoxicants. A clinical study in Egypt found that green tea consumption decreased the oxidative stress induced by benzene exposure in pump workers by improving glutathione levels in the liver.(112) Also, green tea’s iron chelating ability has been found to be beneficial in treating neurodegenerative disorders in laboratory studies.(113)

An in vitro study reported that a green tea extract strongly inhibited Escherichia coli, Streptococcus salivarius and Streptococcus mutans.(79) The antibacterial effect of green and black tea extracts were comparable with those of amoxicillin, cephradine and eugenol.

Of interest is a laboratory study that suggests EGCG application on hair follicles stimulates human hair growth through dual proliferative and anti-apoptotic effects on human dermal papilla cells (DPCs), suggesting a potential application in restoring hair growth.(114)

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