Leaf.
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.
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 contains a catechin known as epigallocatechin gallate (ECGC) which is believed to be responsible for most of the health benefits linked to the tea. 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)
*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.
The most current available medical and scientific literature indicates that this dietary supplement should be standardized to 50-97% polyphenols, containing at least 50% (-)epigallocatechin-3-gallate (EGCG) per dose. Caffeine-free products are recommended, unless the supplement is being used in weight loss management. Then caffeine containing green tea is preferred.
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.
Antioxidant Green tea is reported to have antioxidant properties.(
18),(
19) and the ability to protect against oxidative damage of red blood cells.(
20),(
21) 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.(
22) Green tea’s antioxidant effects seem to be dependent upon the polyphenol (catechin) fraction.(
23),(
24) The antioxidative action of the green tea polyphenols includes trapping the initiating and/or propagating peroxyl radicals and reducing the alpha-tocopheroxyl radical to regenerate alpha-tocopherol.(
25) (-)-epigallocatechin gallate (EGCG), isolated from green tea, displays antioxidant properties
in vitro and is thought to act as an antioxidant in humans.(
26) However, the specific mechanisms of its antioxidant actions remain unclear.
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).(27) One study reported that the addition of milk to any tea may significantly lower the antioxidant potential.(28) However, other studies have reported that milk added to green tea does not effect the antioxidant capacity in humans.(29),(30) It is recommended to use fat-free milk when adding to tea beverages to preserve the antioxidant value.(31)
A study on the antioxidant capacity of green tea catechins was conducted.(32) 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 study investigated the antioxidant effect of green tea ingestion in 10 healthy individuals (5 women, 5 men, ages 23-25).(33) 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.(34) A study compared the chemopreventive effects of green tea and coffee in cigarette smokers.(35) 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.(36)
Positive benefits on the cardiovascular system, particularly blood lipid levels and improved endothelial function, have been reported with the use of green tea.(37),(38) Green tea was reported to lower cholesterol levels by blocking the lipid peroxidation of LDL.(39),(40),(41) 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.(42) Also, an increased resistance of LDL to in vivo oxidation has been reported.(43) 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.(44),(45)
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.(46) Green tea has also been reported to be an inhibitor of thromboxane formation and platelet aggregation, of importance in the prevention of atherosclerosis.(47),(48) Another study found green tea consumption to reduce cardiovascular disease mortality.(49) Researchers found green tea may reduce the risk of cardivascular disease.(50)
Anticarcinogenic Activity
Green tea polyphenols are powerful antioxidants and have been reported to protect in varying degrees against certain cancers, including colon, rectal, bladder,(51) breast,(52) stomach, pancreatic, lung, esophageal(53),(54) prostate.(55),(56),(57),(58) and hematologic malignancies.(59) Further research in the area of green tea consumption and 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.(60) Further, EGCG has been reported to inhibit the growth of cancer cells, lung metastasis in an animal model and urokinase activity.(61),(62) 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.(63),(64) 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.(65) Researchers found there was a 57 percent reduction in the risk of colorectal cancer in women who consumed tea on a regular basis.(66)
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.(67),(68) The exact mechanism(s) of the anticarcinogenic activity remains to be found, but green tea polyphenolics are reported to:(69)
- 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
Recent 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.(70) 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.(71),(72)
Chemotherapy Enhancement and Radiation Protection
The oral administration of green tea reportedly enhanced the inhibitory effects of doxorubicin on tumor growth.(73),(74) 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.(75) Green tea has also been reported to increase the tumor inhibiting effects of Adriamycin (doxorubicin).(76),(77)
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.(78),(79),(80),(81) In vitro studies on human skin have reported similar results.(82) 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.(83) 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.
Other Uses
Arthritis - 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.(84) 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.(85) 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.(86) 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.
Anticariogenic - Human and laboratory studies have supported the use of green tea as a preventative measure in dental caries.(87),(88),(89) Researchers found green tea promoted periodontal health.(90) 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%.(91) 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.(92)
An in vitro study reported that a green tea extract strongly inhibited Escherichia coli, Streptococcus salivarius and Streptococcus mutans.(93) The antibacterial effect of green and black tea extracts were comparable with those of amoxicillin, cephradine and eugenol. Green tea has been found to reduce tooth loss.(94)
Weight Control/ Thermogenic Activity - Recent literature has suggested that green tea may be beneficial in weight control. Recent 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.(95) 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.(96) 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 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 (ECGC) and caffeine with sympathetically released noradrenaline (NA).(97) Results from a study revealed that green tea consumption enhanced weight loss and exercise-induced changes in abdominal fat.(98) Researchers found that a supplement combining green tea and capsaicin suppressed hunger and increased satiety suggesting this supplement may be helpful in preventing weight gain and may also be effective in reducing weight.(99)
Depression - Researchers found that more frequent consumption of green tea was associated with a lower prevalence of depressive symptoms. They went on to indicate that green tea has a component, the amino acid theanine, which is thought to have a tranquilizing effect on the brain, may explain the potentially beneficial effect shown in this study.(100)