Green Tea Antioxidant Properties
- Publish Date: 2009/06/21 - (Rev. 2011/02/14)
- Author: Disabled World
Outline: Scientific studies indicate that green tea may be a helpful antioxidant for many health conditions.
Main DigestAn Italian study found that while green tea was six times more potent in inhibiting lipid peroxidation in vitro, when healthy human subjects ingested the same amount of either black or green tea, the plasma antioxidant capacity (expressed as TRAP, or total radical-trapping antioxidant parameter) was similar in both groups.
The Ingredients of a Green Tea Leaf
Tea leaves contain the following nutrients and substances:
the amino acid theanine
Vitamins A, B1, B2, B3, C, E, F, P, & U
The nature of these ingredients change based on how tea is processed.
More limited processing, such as steaming in the case of white and green tea, retains more of these nutrients and is the basis for the health claims made related to these teas. Roasting and fermenting black teas, and even some types of green teas, can damage the bioactive substances in the tea leaf.
Antioxidant Properties of Tea
An Italian study found that while green tea was six times more potent in inhibiting lipid peroxidation in vitro, when healthy human subjects ingested the same amount of either black or green tea, the plasma antioxidant capacity (expressed as TRAP, or total radical-trapping antioxidant parameter) was similar in both groups.
The increase in plasma antioxidant capacity was quite rapid, peaking at 30-50 minutes. This indicates that the most bioactive antioxidant compounds are quickly absorbed in the upper part of the gastrointestinal system.
The active ingredient in green tea, catechin, has also been found to outperform Vitamin C and beta-carotene ten times in scavenging the alkyl peroxyl radical. One study found green tea polyphenols to be more potent antioxidants than Vitamin C, Vitamin E, rosemary extract, and even curcumin in some systems.
According to the U.S. National Cancer Institute, in laboratory studies using animals, catechins scavenged oxidants before cell damage occurred, reduced the number and size of tumors, and inhibited the growth of cancer cells. White tea is said to be even more effective. However, human studies have proven more contradictory, perhaps due to such factors as variances in diet, environments, and populations.
Some Benefits from Green Tee
Scientific studies indicate that green tea may be helpful for the following health conditions:
Green Tea contains fluorine that helps prevent cavities and strengthens teeth. Green Tea is also said to be able to kill oral bacteria that may cause bad breath.
Studies Relating to Cancer and Green Tea
Breast cancer - A recent Japanese study explored in greater detail the epidemiological findings on green tea's protection against breast cancer.
In this case, women with stage I, II and III breast cancer were assessed in terms of their green tea consumption.
It was found that "pre menopausal women who consumed more green tea had a lower number of lymph node metastases. In postmenopausal women greater consumption of green tea correlated with increased expression of the estrogen and progesterone receptor, which implies more differentiated tumor cells and better prognosis."
Finally, in a seven-year follow it was found that "women with stage I or II cancer who consumed five or more cups of green tea a day had approximately half the recurrence rate of those women who consumed four cups or less."
Researchers at the Department of Surgery, Division of Oncology and. Center for Human Nutrition, University of California found that Inhibition of VEGF transcription appeared to be one of the molecular mechanism(s) involved in the anti-angiogenic effects of green tea, which may contribute to its potential use for breast cancer treatment and/or prevention.
Colorectal cancer - Department of Medicine, Case Western Reserve University researchers found that green tea constituent epigallocatechin-3-gallate inhibits topoisomerase I activity in human colon carcinoma cells.
DNA topoisomerases I and II are essential for cell survival and play critical roles in DNA metabolism and structure. Inhibitors of topoisomerase constitute a novel family of anti-tumor agents with demonstrated clinical activity in human malignancies.
The clinical use of these agents is limited due to severe toxic effects on normal cells. Therefore, there is a need to develop novel, nontoxic topoisomerase inhibitors that have the ability to spare normal cells.
Recent studies have shown that green tea and its major polyphenolic constituent, epigallocatechin-3-gallate (EGCG), impart growth inhibitory responses to cancer cells but not to normal cells.
Based on the knowledge that EGCG induces DNA damage, cell cycle arrest, and apoptosis, the researchers considered the possibility of the involvement of topoisomerase in the anti-proliferative response of EGCG.
Here, for the first time, we show that EGCG inhibits topoisomerase I, but not topoisomerase II in several human colon carcinoma cell lines. Based on this study it is tempting to suggest that combination of EGCG with other conventional topoisomerase inhibitors could be an improved strategy for treatment of colon cancer.
They concluded the role of EGCG as a chemotherapeutic agent needed to be investigated.
The Laboratory for Cancer Research at the College of Pharmacy of, Rutgers University studied the effects of green and black tea polyphenols on normal human colon mucosa and colon cancers were investigated. The results indicated that tea polyphenols can affect arachidonic acid metabolism in human colon mucosa and colon tumors, and this action may alter the risk for colon cancer in humans.
Esophageal cancer - A study done by the College of Pharmacy, Rutgers, The State University of New Jersey, suggest that EGCG was converted to EGC in the oral cavity, and both catechins were absorbed through the oral mucosa through drinking green tea rather than using extracts. Because of the possible application of tea in the prevention of oral and esophageal cancers, the salivary levels of tea catechins were determined in six human volunteers after drinking tea. Saliva samples were collected after thoroughly rinsing the mouth with water.
After drinking green tea preparations equivalent to two to three cups of tea, peak saliva levels of
epigallocatechin (EGC; 11.7-43.9 microg/ml)
EGC-3-gallate (EGCG; 4.8-22 microg/ml)
epicatechin (EC; 1.8-7.5 microg/ml)
were observed after a few minutes. These levels were 2 orders of magnitude higher than those in the plasma.
Taking tea solids in capsules resulted in no detectable salivary catechin level. Holding an EGCG solution in the mouth resulted in EGCG and EGC in the saliva and, subsequently, EGC in the urine. The present results suggest that slowly drinking tea is a very effective way of delivering rather high concentrations of catechins to the oral cavity and then the esophagus.
Leukemia - Another study found that green tea extract is a potent nucleoside transport inhibitor, interfering with tumor cells' repair of DNA after chemotherapy. Thus green tea extract "markedly potentiated" the effectiveness of chemotherapy. These findings suggest that epigallocatechin gallate and green tea extract could be used as a nontoxic adjuvant therapy for leukemia. It would also be interesting to examine how green tea polyphenols synergize with such established anti-leukemic alternative treatments as retinoic acid, Vitamin D3, DMSO, curcumin and esculetin.
Liver cancer - A more recent study, done at the Fels Institute for Cancer Research at Temple University in Philadelphia, found that the addition of .5% of instant green tea powder to the diet of rats changed the metabolism of aflatoxin toward the formation of non-toxic hydroxylated metabolites, and decreased the binding of aflatoxin to liver-cell DNA, significantly decreasing the resulting number of pre-cancerous cells. The authors conclude that green tea protects against aflatoxin-induced liver cancer. Green tea also inhibited liver damage caused by exposure to 2-nitropropane. Even more important, green tea also protected against liver injury caused by galactosamine, which happens to be an animal model of viral hepatitis.
Lung cancer - In a study done at the Karolinska Institute in Stockholm a team of researchers headed by Dr. Yihai Cao found that green tea can block angiogenesis-the development of new blood vessels that tumors need in order to grow and metastasize.
The authors gave mice the equivalent of two-to-three cups of green tea a day. When lung cancer was induced, the mice supplemented with green tea showed significantly less tumor growth. The scientists found that green tea suppressed the development of new blood vessels and prevented metastasis.
They hypothesize the epigallocatechin gallate is the compound responsible for the suppression of angiogenesis. An article in New Scientist magazine (20 March 2004) mentions that numerous studies suggest that green tea protects against a range of cancers, including lung, prostate and breast cancer.
The secret is the antioxidant epigallocatechin gallate (EGCG), according to Hirofumi Tachibana's team at Kyushu University in Japan. Their research showed that growth of human lung cancer cells that have a cell receptor called 67 LR is slowed significantly after drinking just two or three cups of green tea, which contains EGCG. The research also showed that 67 LR is involved in the propagation of prion diseases such as mad cow disease in humans. So knowledge of EGCG's effect on 67 LR might have implications in the treatment of these diseases too. (Full report in Nature Structural and Molecular Biology, DOI:10.1038/nsmb743).
Ovarian cancer - Green tea has also shown promise in other areas. For one, it enhances the effectiveness of chemotherapy in ovarian cancer.
A study done at the University of Shizuoka, Japan, discovered that oral administration of green tea or theanine, an amino acid found in the leaves of green tea, synergized with the chemotherapy drug Adriamycin in lowering tumor weight. Adriamycin alone was ineffective. Theanine nearly tripled the concentration of adriamycin in the tumor tissue, while decreasing adriamycin levels in healthy tissue. In a more recent study, the same authors showed that theanine also synergizes with Adriamycin to inhibit liver metastases of ovarian cancer. This adds to the growing evidence that natural agents such as green tea can greatly enhance the effectiveness of conventional therapies.
Pancreatic cancer- Green tea extract in water was shown to inhibit cancer in rodents in such organs as the stomach, duodenum, colon, liver, and pancreas.
Prostate cancer - In the first known study of the absorption and anti-tumor effects of green and black tea polyphenols in human tissue, researchers at the University of California at Los Angeles were able to detect tea polyphenols in prostate tissue after a very limited consumption of tea.
The study was reported at Experimental Biology 2004, in Washington, D.C., as part of the scientific program of the American Society of Nutritional Sciences, one of the six sponsoring scientific societies of this large multi-disciplinary meeting.
The scientists found that prostate cancer cells grew more slowly when placed in a medium containing blood serum of men who had consumed either green or black tea for five days compared to serum collected before the men began their tea-drinking regimen.
Serum from men who drank comparable amounts of diet or regular soda showed no such slowing in cancer cell proliferation.
Research by Curtin University in Perth Western Australia has shown Green tea drinking over a long period of time helps prevent prostate cancer. Professor Colin Binns studied long time drinkers in China. The big sippers who'd been imbibing for 20 years were 2/3 less likely to develop the cancer than the control group.
Skin cancer - Skin cancer, and the protective effects of catechins on the skin, have been studied extensively.
Ultraviolet radiation is known to cause inflammation and immune, making the skin more susceptible to cancer. High doses of epigallocatechin gallate and other catechins are particularly effective in preventing inflammation and skin cancer, especially if delivered in the topical form.
Topical epigallocatechin gallate was found to reduce the release of inflammatory prostaglandin's (the E2 series), which play a crucial role in generating free radicals and promoting tumor growth.
Due to its anti-mutagenic and anti-tumor activities, green tea is a promising candidate for use in topical formulations for skin cancer prevention.
Epigallocatechin gallate (EGCG) is a potent polyphenolic antioxidant extracted from green tea.
Cima Labs did a study to determine the influence of several factors on the stability of EGCG in solution to obtain information that would facilitate the subsequent development of topical formulations. A second objective was to determine the stability of EGCG in various solvents in the presence and absence of different antioxidants. It was concluded that glycerin-based vehicles are suitable for stabilizing EGCG as a topical formula.
Stomach cancer - Another type of cancer where high consumption of green tea seems to make a difference is stomach cancer.
Men who consumed 7 cups or more of green tea a day had a 31% lower risk of stomach cancer.
A Japanese in vitro study found that both green tea extract and epigallocatechin gallate caused a concentration- and time-dependent growth inhibition and apoptosis (programmed cell death) in a line of human stomach cancer cells.
A recent animal study done at the Alabama A&M University discovered that phytic acid (found in beans and grains) and green tea synergize to significantly reduce the number of pre-neoplastic lesions.
Again, this points to the general principle that two or more natural agents are more effective together.
Other Non-Cancer Conditions
Atherosclerosis Supplementation with antioxidants is important in part because by protecting cholesterol from oxidation, antioxidants help protect against atherosclerosis.
In an animal study comparing the effectiveness of various antioxidants in preventing the oxidation of VDL and LDL cholesterol, vitamin E, genistein (phytoestrogen found chiefly in soy products) and green tea were found to be effective antioxidants, with genistein being particularly effective (oxidation lag time of 49% on the high-genistein diet), but green tea also exerting considerable activity (lag time of 33%).
It would be interesting to see the results of combined genistein and green tea supplementation, particularly in humans. On the other hand, it could be argued that this is precisely the case of the Japanese diet. Japan enjoys the longest life expectancy in the world, and the lowest cardiovascular mortality for men, in spite of heavy smoking.
Brain Functioning - Green tea has been shown to protect the brain from oxidative stress, and lower monoamine oxidase (MAO) activity.
Neurodegenerative diseases have been linked both to free radical damage and to excessive breakdown of neurotransmitters caused by high monoamine oxidase activity.
Green tea in general, as well as its phenolic components catechin and epigallocatechin gallate, have been found to be effective at inhibiting MAO and lowering peroxide levels in glial cells in the brain.
Further evidence that green tea might be useful in preventing age-related brain degeneration comes from studies of the effects of catechins on nerve cell cultures. Thanks to their antioxidant properties, catechins were able to protect the cells from death induced by glucose oxidase. Catechins are also able to restrain the production of nitric oxide by the glial cells surrounding the neurons. Nitric oxide plays an important role as a neurotransmitter involved in memory formation, but excess levels lead to neural death and neurodegenerative disorders.
Flavonoids in general are particularly effective in regulating the levels of nitric oxide in the brain. Green tea is among a handful of substances that can reduce nitric oxide production at concentrations of less than 300 parts per million. The ability to lower lipid peroxidation and to chelate iron in the nervous system is also of tremendous importance.
Parkinson's disease involves the progressive destruction of the dopamine-releasing nigrostriatal dopaminergic system, and hence the ever-increasing dopamine deficiency. It is possible that sufficient green tea consumption might protect against Parkinson's disease.
Both green and black tea are also potent inhibitors of intestinal absorption of non-heme iron, lowering the amount of free iron reaching the brain in the first place.
Japan has a much lower rate of Alzheimer's disease than Western countries.
The Japanese living in Hawaii have 2.5 times the incidence of Alzheimer's disease than do native Japanese in Japan.
It would be interesting to see to what extent the Japanese custom of sipping green tea all day, as contrasted with much lower consumption of green tea by the American-Japanese, contributes to neural protection.
Researchers including Edward Okello of Newcastle University (in northeast England) biology school pitted green tea, black tea, and coffee. They found that tea stops the activity of chemicals in the brain associated with the development of Alzheimer's disease. Symptoms of Alzheimer's disease occur when brain nerve cells that process information and memory degenerate and die. Abnormalities such as plaque and tangles proteins form on nerve cells.
Diabetes - The ability to significantly lower blood glucose has been confirmed also in studies using diabetic rats.
Both green and black tea were shown to possess anti-diabetic activity, and to be effective both in the prevention and treatment of diabetes.
The fact that aged rats responded so dramatically to these polyphenols implies that it is possible to reverse the age-related rise in glucose intolerance and the resulting degenerative cascade of atherosclerosis and other degenerative disorders.
In what way are tea polyphenols able to lower serum glucose? The main mechanism seems to be the inhibition of the activity of starch digesting enzyme amylase. Tea inhibits both salivary and intestinal amylase, so that starch is broken down more slowly, and the rise in serum glucose is thus minimized. In addition, according to one recent study, tea may reduce the intestinal absorption of glucose.
A relatively little known compound found in onions and in tea, especially green tea, called diphenylamine, seems to have a strong sugar-lowering action. Again, the lesson here is that we are barely beginning to identify the significant phenolic compounds and their interactions; it's best not to rely on a single ingredient such as epigallocatechin gallate, but rather to ingest the whole complex set of bioactive compounds present in tea for best results.
Thanks to the serum glucose-lowering effect of tea, we thus obtain significant anti-aging benefits of calorie restriction, reduced glycation, and lower insulin secretion. If you drink tea with a carbohydrate-rich meal, you slow down the release of glucose and reduce its absorption (you also reduce the absorption of iron, another anti-aging benefit). Thus, you prevent the harmful spiking of insulin. Since insulin is our most fattening hormone and, with cortisol, our most pro-aging hormone, you also derive the substantial range of benefits that go with calorie restriction and insulin control.
Heart - Since blood sugar tends to increase with age, accelerating aging by cross-linking with proteins (glycation), the ability of green tea to lower serum glucose levels is extremely important as part of its anti-aging benefits.
Some would argue that tea's ability to lower blood sugar, and thus insulin levels and glycation, is its most important anti-aging property. A study comparing the effects of 75-day feeding of green tea and black tea to aged rats found that green tea lowered blood sugar only slightly better than black tea (23.9% vs 22.8%), but was markedly superior in reducing triglycerides (33.3% vs 25%; high triglycerides are strongly associated a high risk of cardiovascular disease).
A low ratio of triglycerides to HDL is an excellent marker of cardiovascular health. Black tea, however, was a better inducer of super-oxide dismutase (SOD; the activity of SOD was 117% higher in the black tea group vs. control, as compared to 90.8% higher in the green tea group), and a better blocker of the harmful malondialdehyde, a byproduct of lipid peroxidation (black tea reduced it by 34.6%; green tea by 25.4%).
The authors' conclusion that black tea is a more powerful antioxidant in vivo needs to be confirmed by other studies.
High cholesterol - Some very exciting results were found when rats were fed 2.5% green tea leaves in their diet.
The experimental group showed a drop in total cholesterol, low-density cholesterol, and triglycerides.
The body weight of green tea-fed rats was 10 to 18% lower than that of rats not consuming green tea. In addition, the activity of antioxidant enzymes super-oxide dismutase (SOD) and catalase, and of anti-carcinogenic phase-II enzyme glutathione S-transferase (GST), were significantly higher in the green tea group, as was the glutathione level in the liver. There was no liver or kidney toxicity. Thus, the study demonstrated combined cardiovascular and anticancer effects of green tea.
The cholesterol-lowering (hypocholesterolemic) effects of green tea (as well as black tea) have been confirmed by both animal and human epidemiological studies. In addition to lowering the atherogenic index as expressed by the HDL/total cholesterol ratio in rats, green tea and jasmine green tea also reduced the increase of liver weight that results from fat deposition.
High consumption of green tea by humans, especially more than 10 cups a day, was found to be associated with higher HDLs and lower LDL and VLDL cholesterol, as well as with various bio-markers indicating better liver health. Lower levels of lipid peroxides in the liver are one well-confirmed benefit of green tea supplementation, found in study after study.
The pancreas is another organ that is protected by green tea. In a double-blind, randomized, placebo-controlled trial done by Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, 240 adults were given either theaflavin-enriched green tea extract in form of 375mg capsule daily or a placebo. After 12 weeks, patients in the tea extract group have significantly less low-density lipoprotein cholesterol (LDL-C) and total cholesterol (16.4% and 11.3% lower than baseline, p<0.01) then the placebo group. The author concluded that theaflavin-enriched green tea extract can be used together other dietary approaches to reduce LDL-C.
Kidney Health - The kidneys are another area where green tea has shown to have protective effects.
Decreased kidney function due to aging and kidney failure are a frequent cause of death. The public is generally unaware that anything can be done to prevent the age-related decline in kidney function.
Making use of a wide-range of antioxidant protection appears crucial, and flavonoids, including green tea catechins, are very potent antioxidants.
Epigallocatechin gallate was shown to induce antioxidant enzymes in the kidneys, as well as to reduce uremic toxins in the blood, suggesting improved kidney function in an animal model of kidney failure.Kidney problems are often associated with high blood sugar and consequent glycosylation of various proteins (hence the strong link between kidney failure and diabetes).
Since green tea has the ability to lower serum glucose, this is another way in which it helps protect against kidney failure. Likewise, the antioxidant properties of green tea likely play a significant role in protecting the kidneys.
Since green tea has been shown to lower the concentrations of free radicals and lipid peroxides in organs such as the liver and the pancreas, this is likely to be true in the kidneys as well.
Hypertension - Green tea, as well as oolong tea, may also have beneficial effects on hypertension.
In a study done by Yang and other authors, examined the relationship between green and oolong tea and hypertension in 1507 subjects in the Chinese population. Six hundred of the subjects regularly drank green tea. After adjusting for several other variables that may affect the outcome of the results, the authors found that, compared to those who did not regularly drink green tea, those who drank between 120 ml/d and 599 ml/d of green tea for at least one year were 46% less likely to develop hypertension. Those who drank 600 or more ml/d for at least one year were 65% less likely to develop hypertension.
On Weight Loss, Cholesterol Levels and Metabolism
Weight loss studies claim that the polyphenol content of green tea has antioxidant properties that can help prevent cancer. There is also the suggestion that it can increase endurance in exercise by improving fat metabolism.
In a study (American Journal of Clinical Nutrition), researchers looked at the effects of catechins on body fat reduction and weight loss in a group of 35 Japanese men. The men had similar weights based on their BMI (body mass index, an indicator of body fat percentage) and waist sizes.
The men were divided into two groups. For three months, the first group drank a bottle of oolong tea fortified with green tea extract containing 690 milligrams of catechins, and the other group drank a bottle of oolong tea with 22 milligrams of catechins.
During this time, the men ate identical breakfasts and dinners and were instructed to control their calorie and fat intake at all times so that overall total diets were similar.
After three months, the study showed that the men who drank the green tea extract lost more weight (5.3 pounds vs. 2.9 pounds) and experienced a significantly greater decrease in BMI, waist size, and total body fat.
In another study, (Chih-Jen Chang Department of Family Medicine, National Cheng Kung University Hospital, Tainan, Taiwan) a cross-sectional survey of 1210 epidemiologically sampled adults (569 men and 641 women) were enrolled in our study. Tea consumption and other lifestyle characteristics were obtained by structured questionnaires. Percent body fat (BF%) was measured using bio-electrical impedance analysis. Body fat distribution was assessed using waist-to-hip ratio (WHR).
Among the 1103 analyzed subjects, 473 adults (42.9%) consumed tea once or more per week for at least 6 months.
The habitual tea drinkers were male-dominant, more frequently current smokers, and alcohol or coffee drinkers than the non-habitual tea drinkers.
Habitual tea drinkers for more than 10 years showed a 19.6% reduction in BF% and a 2.1% reduction in WHR compared with non-habitual tea drinkers.
The multiple stepwise regression models revealed that men, older age, higher BMI, and current smokers were positive factors for BF% and WHR.
In contrast, longer duration of habitual tea consumption and higher total physical activity were negative factors for BF%.
Longer duration of habitual tea consumption, higher socioeconomic status, and pre-menopausal status were negative factors for WHR.
In a study reported on in the American Journal of Clinical Nutrition, it was found that green tea extract resulted in a significant increase in energy expenditure (a measure of metabolism), plus also had a significant effect on fat oxidation. While some of the effects were originally theorized to be due to the caffeine content of green tea, the researchers discovered that the tea actually has properties that go beyond those that would be explained by the caffeine.
Green tea appears to speed up calorie burning, including fat calorie burning. The green tea extract may play a role in the control of body composition.
Researchers studied the effects of green tea on 10 healthy young men, average age 25, who ranged from lean to mildly overweight. For 6 weeks, the men took two capsules at each meal: green tea extract plus 50 milligrams of caffeine; 50 milligrams of caffeine; or a placebo (inactive capsule).
The study participants were on a weight maintenance diet of about 13% protein, 40% fat, and 47% carbohydrates, a "typical Western diet." Three times during the study, the men spent 24 hours in a special room where the investigators measured their respiration and energy expenditure. Energy expenditure, the number of calories used during a 24-hour period, was higher for men taking green tea extract than for those taking caffeine or placebo. They also found evidence that men taking the green tea extract used more fat calories than those taking the placebo.
Clinical trials conducted by the University of Geneva, in Switzerland indicate that green tea raises metabolic rates and speed up fat oxidation. In addition to caffeine, green tea contains catechin polyphenols that raise thermogenesis (the rate at which calories are burned) and hence increases energy expenditure.