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Seen a few posts with questions about Green Tea so I though I would post this.
Green tea
All true teas—as distinct from herbal and flower infusions, which afficiandos call tisanes—are made from the leaves of a magnolia-related evergreen tree with the botanical name of Camellia sinensis. Although reaching a height of 30 feet in the wild, on tea plantations (called gardens or estates), the plant is kept as a shrub, constantly pruned to a height of about 3 feet to encourage new growth and for convenient picking.
Tea plants grow only in warm climates but can flourish at altitudes ranging from sea level to 7,000 feet. The best teas, however, are produced by plants grown at higher altitudes where the leaves mature more slowly and yield a richer flavor. Depending upon the altitude, a new tea plant may take from 2 ½ to 5 years to be ready for commercial picking, but once productive, it can provide tea leaves for close to a century.
Tea plants produce abundant foliage, a camellia-like flower, and a berry, but only the smallest and youngest leaves are picked for tea—the two leaves and bud at the top of each young shoot. The growth of new shoots, called a flush, can occur every week at lower altitudes but takes several weeks at higher ones. The new leaves are picked by hand by "tea pluckers," the best of whom can harvest 40 pounds per day, enough to make 10 pounds of tea.
All tea plants belong to the same species—Camellia sinensis—, but local growing conditions (altitude, climate, soils, etc.) vary, resulting in a multitude of distinctive leaves. The way the leaves are processed, however, is even more important in developing the individual characteristics of the three predominant types of tea: green, black and oolong.
Green tea is the least processed and thus provides the most antioxidant polyphenols, notably a catechin called epigallocatechin-3-gallate (EGCG), which is believed to be responsible for most of the health benefits linked to green tea. Green tea is made by briefly steaming the just harvested leaves, rendering them soft and pliable and preventing them from fermenting or changing color. After steaming, the leaves are rolled, then spread out and "fired" (dried with hot air or pan-fried in a wok) until they are crisp. The resulting greenish-yellow tea has a green, slightly astringent flavor close to the taste of the fresh leaf.
In black tea production, the leaves are first spread on withering racks and air-blown, which removes about one-third of their moisture and renders them soft and pliable. Next, they are rolled to break their cell walls, releasing the juices essential to fermentation. Once again, they are spread out and kept under high humidity to promote fermentation, which turns the leaves a dark coppery color and develops black tea's authoritative flavor. Finally, the leaves are "fired," producing a brownish black tea whose immersion in hot water gives a reddish-brown brew with a stronger flavor than green or oolong teas.
Oolong tea, which is made from leaves that are partially fermented before being fired, falls midway between green and black teas. Oolong is a greenish-brown tea whose flavor, color and aroma are richer than that of green tea, but more delicate than that of black.
Green tea has always been, and remains today, the most popular type of tea from China where most historians and botanists believe the tea plant originated throughout all of Asia. Why is this so? Perhaps because green tea not only captures the taste, aroma and color of spring, but delivers this delightful bouquet along with the highest concentration of beneficial phytonutrients and the least caffeine of all the teas.
Health Benefits
Description
History
How to Select and Store
How to Enjoy
Safety
Nutritional Profile
References
Health Benefits
Green tea is particularly rich in health-promoting flavonoids (which account for 30% of the dry weight of a leaf), including catechins and their derivatives. The most abundant catechin in green tea is epigallocatechin-3-gallate (EGCG), which is thought to play a pivotal role in the green tea's anticancer and antioxidant effects. Catechins have been found to be more potent free radical scavengers than the well known antioxidants vitamins E and C.
Most of the research showing the health benefits of green tea is based on the amount of green tea typically consumed in Asian countries—about 3 cups per day (which would provide 240–320 mg of polyphenols). Just one cup of green tea supplies 20-35 mg of EGCG, which has the highest antioxidant activity of all the green tea catechins.
The health benefits of green tea have been extensively researched and, as the scientific community's awareness of its potential benefits has increased, so have the number of new studies. As of November 2004, the PubMed database contained more than 1,000 studies on green tea, with more than 400 published in 2004! Following is a brief summary of some of the high points of this most current research.
Green tea drinkers appear to have lower risk for a wide range of diseases, from simple bacterial or viral infections to chronic degenerative conditions including cardiovascular disease, cancer, stroke, periodontal disease, and osteoporosis. The latest studies provide a deeper understanding of the ways in which green tea:
Protects against Coronary Artery Disease
In Japanese studies, green tea consumption has been found to be an independent predictor for risk of coronary artery disease. In one study, those drinking 5 or more cups of green tea each day were found to be 16% less likely to suffer from coronary artery disease. The relationship was so significant researchers concluded, "The more green tea patients consume the less likely they are to have coronary artery disease."
An elevation in the amount of free radicals in the arteries is a key event in many forms of cardiovascular disease. The latest research shows that green tea catechins inhibit the enzymes involved in the production of free radicals in the endothelial lining of the arteries. The arterial endothelium is a one-cell thick lining that serves as the interface between the bloodstream and the wall of the artery where plaques can form. By protecting the endothelium from free radical damage, green tea catechins help prevent the development of cardiovascular disease.
Inhibits Atherosclerosis
Green tea has been shown to effectively lower risk of atherosclerosis by lowering LDL cholesterol, triglycerides, lipid peroxides (free radicals that damage LDL cholesterol and other lipids or fats) and fibrinogen (a protein in the blood involved in the formation of blood clots), while improving the ratio of LDL (bad) to HDL (good) cholesterol. In animal studies in which green tea was given in human equivalent doses to hamsters, atherosclerosis was inhibited 26-46% in those receiving the lower dose (equivalent in humans to 3-4 cups per day) , and 48-63% in those receiving the higher dose (10 cups a day in humans).
Special Benefits for Persons with High Triglycerides
Green tea may offer special heart-protective benefits for persons with high triglycerides, suggests a laboratory study, published in the February 2005 issue of the Journal of Nutrition.
A series of experiments revealed that the mix of catechins naturally found in green tea dose-dependently inhibit the activity of pancreatic lipase, the enzyme secreted by the pancreas that digests fat. As a result, the rate at which the body breaks down of fats into triglycerides, and the rise of triglyceride levels in the bloodstream that occurs after meals, is greatly slowed. Since a large rise in blood levels of triglycerides after a meal is a significant risk factor for coronary heart disease, drinking a cup of two green tea along with your meals is a good idea, especially if your triglyceride levels are higher than normal.
Thins the Blood and Helps Prevent Blood Clots
Green tea catechins help thin the blood and prevent the formation of blood clots by preventing the formation of pro-inflammatory compounds derived from omega-6 fatty acids, which are found in meats and polyunsaturated vegetable oils such as corn, safflower and soy oil. These pro-inflammatory compounds—specifically, arachidonic acid from which the inflammatory cytokines thromboxane A2 and prostaglandin D2 are derived—cause platelets to clump together.
Protects the Heart in Patients with Acute Cardiovascular Disease
The primary catechin in green tea, EGCG (epigallocatechin-3-gallate) confers such powerful protection that it can help prevent the death of heart muscle cells following ischemia/reperfusion injury. Ischemia is the medical term for a restriction in blood supply and therefore in oxygen and nutrients. When circulation is restored, oxidative damage occurs, and this is referred to as reperfusion injury. EGCG prevents heart muscle damage by blocking the activation of inflammation-related compounds (including NF-kappa-B and STAT-1) that play a critical role in promoting the oxidative damage that kills heart cells in reperfusion injury. Researchers believe EGCG can be used to help minimize damage in patients with acute coronary artery disease.
Minimizes Damage and Speeds Recovery after a Heart Attack
Research conducted over the last several years by Dr. Anastasis Stephanou and his team at the UK's Institute of Child Health and published in the FASEB Journal, the journal of the Federation of Experimental Biology and the Journal of Cellular and Molecular Medicine has focused on EGCG's ability to block the action of the protein, STAT-1. Normally activated in cells after a heart attack or stroke, STAT-1 plays a major role in inducing cell death.
Not only does green tea minimize heart cell death after a heart attack or stroke, ECGC also appears to speed up heart cells' recovery from damage, allowing the tissues to recover more quickly and alleviating damage to organs. Dr. Stephanou, a molecular biologist, noted: "We're extremely encouraged by these findings and hope to implement them in the clinical setting to minimize cell death activation in patients with acute coronary heart disease."
Minimizes Damage to the Brain after a Stroke
EGCG has also been shown to protect brain cells by these same mechanisms and thus may help minimize the brain damage that occurs after a stroke. In one animal study, green tea was so effective in reducing the formation of free radicals in brain tissue that the researchers concluded, "Daily intake of green tea catechins efficiently protects the brain from irreversible damage due to cerebral ischemia, and consequent neurologic deficits."
Lowers Blood Pressure and Helps Prevent Hypertension
A study published in the July 2004 issue of the Archives of Internal Medicine found that among persons consuming tea regularly for at least one year, the risk of developing high blood pressure was 46% lower among those who drank ½ cup to 2 ½ cups per day, and 65% less among those consuming more than 2 ½ cups per day.
In another study, this one of rats bred not only have high blood pressure but also to be prone to strokes, those rats given green tea had significantly lower systolic and diastolic blood pressure compared to controls, who received plain water. The animals in this study, which was published in the January 2004 issue of the Journal of Nutrition, consumed the human equivalent of 1 liter (1.1 quarts or a little more than 4 cups) of green tea per day.
Helps Prevent the Development of Atherosclerosis and Cancer
In both atherosclerosis and cancer, cell growth and proliferation is central to the disease process. In atherosclerosis, plaques form in the lining of the arteries, which grow thicker and less elastic, impeding blood flow. In cancer, normal brakes on cells turn off, and they multiply out of control. Green tea can help stop abnormal cell proliferation.
Catechins, among the main active compounds in green tea leaves, shut down the primary relay station through which growth factors central to both atherosclerosis and cancer send their messages for growth. These relay stations, called tyrosine kinase receptors, are essential for the transmission of messages sent by platelet derived growth factor, insulin-like growth factor, epidermal growth factor, fibroblast growth factor, and vascular endothelial growth factor. The result is the prevention of or halting of the disease processes that depend upon excessive cellular growth.
Two other damaging factors that cause the cells lining our vasculature to proliferate are AGEs (advanced glycation end products) and MAPK (mitogen-activated protein kinase). AGEs form when sugars inappropriately bind to and distort proteins. MAPK activity is normally enhanced in the presence of elevated levels of LDL cholesterol. In laboratory studies, green tea polyphenols were shown to dose-dependently inhibit AGE-stimulated proliferation of vascular smooth muscle cells and to prevent the increase in MAPK normally seen when LDL levels are high.
Protects against Cancer
In the last ten years, green tea's cancer-preventive effects have been widely supported by epidemiological, cell culture, animal and clinical studies. For cancer prevention, the evidence is so overwhelming that the Chemoprevention Branch of the National Cancer Institute has initiated a plan for developing tea compounds as cancer-chemopreventive agents in human trials.
When confronted with a cancerous cell, green tea becomes the plant kingdom's Arnold Schwarzenegger, helping to terminate cancer cells in a remarkable number of ways.
Laboratory cell culture studies show that green tea polyphenols are powerful triggers of apoptosis (cell suicide) and cell cycle arrest in cancerous but not in normal cells. (Cell cycling is the process cells go through to divide and replicate.)
These anticancer actions have been assumed to be due to the powerful antioxidant effects of green tea's catechins, especially epigallocatechin-3-gallate (EGCG). This is a reasonable assumption, given that a number of studies have shown that green tea possesses remarkable antioxidant properties. In one study published in the November 2004 issue of Mutation Research, EGCG's protective antioxidant effects against several carcinogens were found to be 120% stronger than those of vitamin C.
But while green tea's antioxidant prowess is impressive, recent studies show it is far from the only way in which this multi-talented beverage protects us against cancer.
One of these mechanisms is green tea's ability to inhibit angiogenesis, the development of new blood vessels. Cancer cells, which are constantly attempting to divide and spread, have an endless appetite that can only be temporarily quieted by increasing the number of blood vessels that supply them with nutrients. By inhibiting angiogenesis, green tea helps starve cancer.
Studies also show that green tea works at the genetic level, shutting off genes in cancerous cells that are involved in cell growth, while turning on those that instruct the cancer cells to self-destruct. EGCG has even been found to work as a pro-oxidant or free radical, but just inside cancer cells, where it causes so much damage that the cancer cells' self-destruct mechanisms are triggered.
A study of ECGC's effects on keratinocytes (the major type of epidermal or skin cell) found that this green tea compound has yet another means of correcting cancer—that of turning on the genes that direct the cancer cell to return to normal.
Green tea's anticancer effects include its ability to inhibit the overproduction of the enzyme cyclooxygenase (COX)-2, a protein whose overproduction has been implicated as a factor in many diseases, including arthritis and cancer. COX-2 has an enzyme counterpart, called COX-1, which may be helpful to leave untouched when preventing overproduction of COX-2. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin and ibuprofen (which inhibit both COX-1 as well as COX-2), and specific COX-2 inhibitors such as Vioxx and Celebrex (which inhibit only COX-2), have been considered as possible agents in the prevention of some forms of cancer, but their severe toxic side effects on normal cells limit their usefulness. In studies of prostate cancer cells, EGCG appears to block only COX-2 and to have no negative side effects.
Prostate Cancer
EGCG provides other benefits specific to prostate cancer prevention. A study published in the December 2004 issue of the International Journal of Cancer found that EGCG significantly inhibited, in a dose-dependent manner, the production of prostate-specific antigen (PSA), a marker for prostate cancer risk. Not only did EGCG lower PSA levels, but it also suppressed all the activities of PSA which were examined that promote prostate cancer.
Green tea polyphenols halt prostate cancer at multiple levels
The polyphenols in green tea help prevent the spread of prostate cancer by mobilizing several molecular pathways that shut down the proliferation and spread of tumor cells, while also inhibiting the growth of blood vessels that supply the cancer with nourishment, according to research published in the December 2004 issue of Cancer Research.
Green tea polyphenols:
decrease insulin-like growth factor-1 (IGF-1), while increasing levels of IGF binding protein-3, which binds IGF-1, further diminishing its activity. (Increased levels of IGF-1 are associated not only with prostate cancer, but cancers of the breast, lung and colon.)
inhibit key cell survival proteins, promoting apoptosis or programmed cell death in cancer cells.
reduce the expression of several compounds (urokinase plasminogen activator and matrix metalloproteinase 2 and 9) involved in the metastasis and spread of cancer cells.
reduce the amount of vascular endothelial growth factor (VEGF), which develops new blood vessels to carry nutrients to developing tumors.
All these effects were seen in this animal study within 6 months of continuous infusion. While obviously impractical for humans, the study suggests that daily consumption of green tea may be highly protective.
Ovarian Cancer
Green tea consumption has been shown to enhance survival in women with ovarian cancer. In a study published in the November 2004 issue of the International Journal of Cancer, women with ovarian cancer who drank at least 1 cup of green tea daily had a 56% lowered risk of death during the 3 years of the study compared to non-tea drinkers. A laboratory study of human ovarian cancer cells published in the September 2004 issue of Gynecologic Oncology explains why: EGCG not only suppresses the growth of ovarian cancer cells, but also induces apoptosis (cell suicide) in these cells by affecting a number of genes and proteins.
An epidemiological (population) study published in the December 2005 issue of the Archives of Internal Medicine, adds more evidence that enjoying a cup or two of tea each day may significantly lower a woman's risk of ovarian cancer.
Data from numerous other studies has suggested that both green and black tea may offer protection against various cancers, with tea polyphenols thought to be the most likely protective agents. In this research, Susanna Larsson and Alicja Wolk from the National Institute of Environmental Medicine, Stockholm, Sweden, decided to look specifically at the relationship between tea consumption and ovarian cancer.
Participants in their study were 61,057 Swedish women aged 40-76 years who were in the Swedish mammography cohort and had completed a validated 67 item food frequency questionnaire at baseline (between 1987-1990), after which the women were followed an average of 15.1 years.
Analysis of the data found that even women who averaged less than one cup of tea per day had an 18% lower risk of ovarian cancer than non-tea-drinkers.
Those who drank one cup per day had a 24% lower risk, and those who drank two or more cups of tea per day had a 46% lower risk of ovarian cancer than non-tea-drinkers.
Each additional cup of tea per day was associated with an 18% lower risk of ovarian cancer. Although higher tea consumption was generally associated with other health-promoting behaviors, including higher consumption of fruits and vegetables, when compared to the lifestyle behaviors of those who seldom or never drank tea, the large drop in ovarian cancer risk seen as tea consumption increased does suggest that tea is likely to offer significant protection.
Breast Cancer
Recent studies have also identified two mechanisms through which green tea works against breast cancer. Not only does EGCG inhibit the activity of telomerase, an enzyme that plays a key role in cell division, in breast cancer cells, but it also offers help to women with estrogen-negative breast cancer, a form of breast cancer that is very hard to treat successfully.
Estrogen-negative breast cancer cells express high amounts of the epidermal growth factor Her-2/neu, while in the more treatable estrogen-positive form of breast cancer, estrogen-receptor alpha (ERalpha) is expressed. According to a study published in the October 2004 issue of Molecular and Cellular Biology, EGCG induces the expression of ERalpha rather than Her-2/neu in breast cancer cells.
Brain Tumors in Children
Green tea's ability to inhibit telomerase may also translate into help for children with the most common malignant brain tumors of childhood, primitive neuroectodermal tumors. Telomerase's activity allows cancer cells to avoid the normal limits on the number of times a cell can replicate before it self-destructs. In a study published in the January 2004 issue of Neuro-oncology, investigators found that telomerase activity was at least five times higher in children with these brain tumors than in normal brain cells and that EGCG strongly inhibited telomerase activity in a dose-dependent manner.
Colon Cancer
Green tea may also reduce the increased risk for colon cancer caused by a high fat diet. An animal study published in the journal Nutrition and Cancer in 2003 found that when green tea was given along with a diet high in omega 6 fat (in the form of corn oil), the amount of pro-inflammatory compounds produced in the colon (5-lipoxygenase, leukotriene A4 hydrolase, and leukotriene B4) was significantly lower, as was the resulting number of precancerous colon cells (aberrant crypt foci). Green tea consumption even reduced the amount of abdominal fat produced in the animals that received it compared to controls.
Lung Cancer
While we certainly do not recommend smoking, if you or someone you love smokes, or if you must be around smokers and are exposed to second hand smoke, drinking green tea can offer some protection against lung cancer. A human pilot study recently confirmed the protective effects of green tea against lung cancer seen in cell culture and animal studies. The study, published in the November 2004 issue of Molecular Nutrition and Food Research evaluated the effect of green tea (5 cups per day) on 3 heavy smokers (>10 cigarettes a day) and 3 individuals who had never smoked. When the study subjects were drinking green tea, DNA damage caused by smoking was decreased, cell growth was inhibited, and cellular triggers for apoptosis (cell suicide) in abnormal cells increased.
Another larger four month study of heavy smokers involving 100 women and 33 men found that levels of urinary 8-hydroxydeoxyguanosine, a marker of free radical damage to DNA, dropped significantly in individuals drinking decaffeinated green but not black tea. Decaffeinated green tea was especially effective in reducing DNA damage in individuals who lack the genetic ability to produce normal amounts of an enzyme called glutathione S-transferase, which plays a key role in the liver's ability to detoxify many of the carcinogens found in cigarette smoke. Individuals whose genetic inheritance does not include the GSTM1 and GSTT1 variants of the genes that instruct the cell to produce glutathione S-transferase are more susceptible to developing many different cancers. For these individuals, green tea may be especially beneficial.
Bladder Cancer
Research by a multi-departmental team from UCLA has produced valuable insights into how green tea extract might be capable of acting against the invasive growth of bladder cancer tumors. Green tea extract has been shown, via a mechanism that affects cell movement, to target cancer cells while leaving healthy cells alone.
For cancer to grow and spread, the malignant cells must be able to move, and their movement depends on a process called actin remodeling, which itself is carefully regulated by complex signaling pathways, including the Rho pathway.
By inducing Rho signaling, green tea causes cancer cells to mature more rapidly and to bind together more closely, a process called cell adhesion. Both their increased maturity and cell adhesion inhibit cancer cells' mobility, according to Rao, senior author of the study, published in the February 2005 issue of Clinical Cancer Research, in which green tea's effects on Rho signaling were noted.
"Cancer cells are invasive and green tea extract interrupts the invasive process of the cancer…In effect, the green tea extract may keep the cancer cells confined and localized, where they are easier to treat and the prognosis is better," explained Rao.
About 56,000 new cases of bladder cancer are diagnosed each year, making it the fifth most common cancer in the United States. About half of all bladder cancers are believed to be related to cigarette smoking. Bladder cancer can be difficult to detect in the early, most treatable stages, yet, when not found early, the tumors can be aggressive, and more than half of patients with advanced cancers experience recurrences. In the next phase of his research, Rao and his team will analyze urine from bladder patients, looking particularly for biomarkers associated with actin remodelling and the activation of the Rho pathway, to determine which subset of patients might benefit most from green tea.
Improves the Efficacy of Cancer Drugs While Lessening Their Negative Side-Effects
In the fight against cancer, green tea polyphenols are team players, helping cancer-killing drugs do their job. In a study published in the October 2004 issue of the Journal of Pharmacy and Pharmacology, green tea polyphenols caused drug-resistant cancer cells, which were able to extrude or push out one of the most commonly used cancer drugs, doxorubicin, to retain the drug, which could then destroy them. According to a study published in the August 2004 issue of Cancer Letters, another compound in green tea, the amino acid theanine, reduces the negative side effects of doxorubicin by increasing the level of one of the body's most important internally produced antioxidants, glutathione, in normal tissues in the liver and heart—but not in tumors.
Understanding How Green Tea Fights Cancer
Spanish and British scientists have discovered at least one of the mechanisms through which green tea helps to prevent certain types of cancer, according to a study published in the March 2005 issue of Cancer Research.
ECGC, a catechin present in green tea in amounts about 5 times higher than in black tea, inhibits the enzyme dihydrofolate reductase (DHFR), which cancer cells need to be able to grow, and which is a well recognized target of anti-cancer drugs.
Scientists decided to look at ECGC after they realized the green tea catechin looks a lot like the cancer drug methotrexate, which prevents cancer cells from making DNA by inhibiting the DHFR enzyme. They discovered that ECGC kills cancer cells in the same way as the drug.
Although ECGC binds strongly to DHFR, which is essential in both healthy and cancerous cells, it does not bind as tightly as methotrexate, so its side effects on healthy cells are less severe than those of the drug.
ECGC's binding to DHFR may also explain why women who drink large amounts of green tea around the time they conceive and early in their pregnancy may have an increased risk of having a child with spina bifida or other neural tube disorders.
Women are advised to take supplements of folic acid when trying to conceive and during the first trimester (the first 3 months) of pregnancy because it is during this time period that the baby's neural tube is developing. Folic acid helps ensure normal development and protects against spina bifida by enabling the production of the enzyme DHFR. While a cup or two of green tea is unlikely to pose a problem, drinking large amounts of green tea could decrease the activity of DHFR, increasing risk of neural tube defects.
Improves Insulin Sensitivity in Type 2 Diabetes
Population studies suggest that green tea consumption may help prevent type 2 diabetes. A number of animal studies are beginning to explain why. New studies suggest that green tea may improve glucose tolerance and insulin sensitivity in individuals with diabetes. In one study, after receiving green tea for 12 weeks, diabetic rats had lower fasting blood levels of glucose, insulin, triglycerides and free fatty acids compared to controls, and the ability of their adiopcytes (fat cells) to respond to insulin and absorb blood sugar greatly increased.
In another study by the same research group, diabetic rats were separated into three groups and followed for 12 weeks. One group was given with standard rat chow and water (the control group), the second group received a high fructose diet and water (fructose group), and the third group got the same high fructose diet and green tea (green tea group). By the end of the study, the fructose group had high blood sugar, high insulin levels, and high blood pressure, while the animals receiving green tea along with a high fructose diet showed improvement in all three.
A study published in the August 2004 issue of BMC Pharmacology, in which oral glucose tolerance tests were given to healthy humans after they consumed green tea, showed that it increased the body's ability to utilize blood sugar.
Another interesting animal study compared the effects of a Western diet, a vegetarian diet and a Japanese diet, each with or without green tea. Blood sugar concentrations were highest in the animals on the Western diet followed by the Vegetarian diet with the Japanese diet producing the lowest blood sugars. When supplemented with green tea, blood sugar levels dropped in rats on all three diets, with those on the Japanese diet having not only the lowest blood sugars but also rating the best on other risk factors for type 2 diabetes. Rats on the Japanese diet that also were given green tea had the lowest triglycerides and cholesterol as well as the highest ratio of beneficial omega-3 fatty acids to potentially inflammatory omega-6 fatty acids. The researchers concluded that Japanese eating habits combined with drinking green tea might help prevent type 2 diabetes.
One of the mechanisms through which green tea improves insulin sensitivity has recently been identified in laboratory studies that show that epigallocatechin 3-gallate (EGCG) does a good deal more to prevent type 2 diabetes than lower the production of free radicals. EGCG also works on the genetic level, causing a reduction in the number of messenger RNAs that direct liver cells to produce the enzymes involved in the creation of glucose (sugar).
Protects against Kidney Disease
An animal study published in the January 2005 issue of Pharmacological Research suggests yet another beneficial effect of green tea consumption: the prevention of kidney dysfunction in persons who must take powerful immunosuppressant drugs, for example, after an organ transplant.
One such drug, cyclosporine A, while a very effective immunosuppressant, also markedly elevates the production of free radicals highly toxic to the kidneys. In this study, rats given green tea as their drinking water along with cyclosporine A produced far fewer damaging free radicals than rats given plain water. In addition, a number of other indicators of kidney function (serum creatinine, blood urea nitrogen, uric acid and urinary excretion of glucose) were significantly better in rats given green tea.
Another animal study published in May 2004 in the Annals of Nutrition & Metabolism explains why. Diabetic rats given green tea catechins and then exposed to a kidney-damaging drug, streptozotocin, produced less than half the amount of superoxide radicals (a particularly damaging type of free radical) compared to diabetic rats on a catechin-free diet. As a result, a cellular waste product formed by free radical damage to fats, lipofuscin, was almost 200% higher in the diabetic rats who did not receive green tea catechins compared to those who did.
Prevents Osteoporosis and Periodontal diseases
Excessive bone loss is a characteristic feature not only of osteoporosis but of periodontal disease. Green tea supports healthy bones and teeth both by protecting osteoblasts (the cells responsible for building bone) from destruction by free radicals, and by inhibiting the formation of osteoclasts (the cells that break down bone).
Another benefit of green tea consumption for those with periodontal disease: green tea short circuits the damaging effects of the bacteria most responsible for gum disease, Porphyromonas gingivalis. P. gingivalis causes gum damage by producing toxic byproducts such as phenylacetic acid and by stimulating the activity and production of enzymes called metalloproteinases (MMPs), which destroy both the mineral and organic constituents that make up the matrix of our bones. Epigallocatechin-3-gallate (EGCG) inhibits P. gingivalis' production of both phenylacetic acid and MMPs.
Protects the Liver from Alcohol and Other Harmful Chemicals
Alcohol metabolism results in the production of damaging free radicals that can overwhelm the liver's supply of antioxidants, resulting in liver injury. In a study published in the January 2004 issue of Alcohol in which rats were chronically intoxicated with alcohol for 4 weeks, green tea prevented damage to their livers.
Other animal research shows that epigallocatechin-3-gallate (EGCG) protects the liver against the free radicals generated when mice are exposed to carbon tetrachloride, a toxic chemical solvent. Without the protection afforded by EGCG, carbon tetrachloride exposure resulted in the production of numerous free radicals that destroyed a significant amount of the animals' liver cells. With EGCG, free radical production and liver injury was so greatly reduced that researchers suggested green tea should be used in the treatment of liver disease.
Unlike some herbs, green tea's protective effects do not appear to affect two of the liver enzymes most often responsible for detoxifying and eliminating drugs, cytochrome P-450 2D6 and 3A4. This suggests that green tea might be safely consumed when taking medications primarily dependent upon the CYP2D6 or CYP3A4 pathways of metabolism. Hopefully, future research studies will bear out this potential benefit.
On the other hand, one study found that Japanese green tea did increase the activity of the CYP1A1 enzyme. Researchers hypothesized that the increase in activity of this liver enzyme may be one of the ways in which green tea helps protect against cancers caused by various dietary carcinogens.
Promotes Fat Loss
Green tea not only promotes fat loss, but specifically, the loss of visceral fat—fat that accumulates in the tissues lining the abdominal cavity and surrounding the intestines (viscera) and internal organs. Unlike fat deposits on the hips and thighs (which result in the so-called "pear" body shape), visceral fat (which produces the "apple" body shape) is highly associated with increased risk for metabolic syndrome and type 2 diabetes. Green tea contains three major components that promote fat loss: catechins, caffeine and theanine. Studies suggest that green tea compounds promote fat loss by inhibiting both gastric and pancreatic lipase, the enzymes that digest triglycerides, and fatty acid synthetase, the enzyme responsible for synthesizing fatty acids into the form in which they can be stored in the body's adipose (fat) cells.
In a study published in the January 2004 issue of In Vivo in which mice were fed diets containing 2% green tea powder for 16 weeks, visceral fat decreased by 76.8% in those receiving green tea compared to the control group. Green tea also decreased blood levels of triglycerides (the chemical form in which most fats exist in the body).
A human study, published in the January 2005 issue of the American Journal of Clinical Nutrition, confirms green tea's ability to not only reduce body fat, but damage to LDL cholesterol as well. After 12 weeks of drinking just one bottle of green tea each day, 38 normal-to-overweight men in Tokyo had a significantly lower body weight, BMI, waist circumference, body fat mass and amount of subcutaneous fat compared to men given a bottle of oolong tea each day.
After a 2 week diet run-in period, the men were divided into two groups, one of which drank a bottle of green tea containing 690 mg of catechins, while the other group drank a bottle of oolong tea containing 22 mg catechins.
Not only did the men drinking green tea lose weight and fat, but the amount of their LDL cholesterol damaged by free radicals also dropped significantly. Since atherosclerotic plaques develop when cholesterol circulating in the bloodstream is damaged or oxidized, green tea's ability to prevent these oxidation reactions may explain some of its protective effects against cardiovascular diseases.
Increases Exercise Endurance
Green tea extract given to lab rats over a 10-week span increased the amount of time the animals could swim before becoming exhausted by as much as 24%.
Green tea's catechins appear to stimulate the use of fatty acids by liver and muscle cells. In muscle cells, the ability to burn more fat translates into a reduction in the rate at which glycogen, the form in which carbohydrates are stored for ready access in muscle, is used up, thus allowing for longer exercise times. Green tea's effect on muscle cells' ability to take in and burn fatty acids, speeding up fat breakdown, is also thought to be the reason why it helps weight loss.
The idea for the experiment came from the fact that skeletal muscles utilize carbohydrates, lipids (fats) and amino acids (protein) as energy sources, but the ratio in which they are used varies with the intensity and type of the exercise, and the level of the individual's fitness. During endurance exercise, the use of too much carbohydrate is undesirable because it triggers insulin secretion, which, in turn, both inhibits the burning of fatty acids and stimulates lactic acid production. (Lactic acid buildup is what causes that sore achy feeling in your muscles when you exercise.) Conversely, enhanced availability and utilization of free fatty acids reduces carbohydrate utilization, which in turn spares glycogen (the form in which carbohydrates are stored in muscle for quick use) and suppresses lactic acid production, resulting in an increase in endurance."
Drinking a single cup of green tea before exercise, however, will not be effective. One single, higher "dose" of green tea did nothing to improve lab rats' performance. The animals had to receive green tea daily, and endurance increased gradually over the 10 weeks of the study. To match the beneficial effect on test animals' endurance capacity seen in the experiments, the researchers estimate a 165-pound athlete would need to drink about 4 cups of green tea daily.
Protects against Cognitive Decline, Alzheimer's Disease and Parkinson's Disease
Damage to brain cells in Parkinson's, Alzheimer's and other neurodegenerative diseases seems to result from the combination of a number of damaging factors including excessive inflammation and increased levels of iron, both of which lead to increased free radical production, exhaust the brain's supply of protective antioxidants and trigger the production of certain proteins, such as amyloid-beta, which promote apoptosis (cell suicide).
Green tea catechins, until recently thought to work simply as antioxidants, are now known to invoke a wide spectrum of neuroprotective cellular mechanisms. These include iron chelation, scavenging of free radicals, activation of survival genes and cell signaling pathways, and regulation of mitochondrial function. (The mitochondria are the energy production factories inside our cells. When they are not working properly, they generate many free radicals and little energy.) The end result is a significant lessening of damage to brain cells.
Iron accumulation in specific brain areas and free radical damage to brain cells are considered the major damaging factors responsible for a wide range of neurodegenerative disorders including both Parkinson's and Alzheimer's disease.
In the brain, epigallocatechin-3-gallate (EGCG) has been shown to act as an iron chelator, binding to and removing iron, thus preventing it from contributing to the production of free radicals. In addition to removing iron, EGCG also increases the activity of two major antioxidant enzymes, superoxide dismutase (SOD) and catalase, further helping to decrease free radical damage.
Another active compound in green tea, epicatechin (EC), reduces the formation of a protein called amyloid-beta. Plaque-like deposits of amyloid-beta in the brain are a defining characteristic of Alzheimer's disease.
Green tea polyphenols have also demonstrated the ability to affect cell signaling pathways, in particular the MAPK pathways, which are triggered by oxidative stress (free radicals), and themselves set in motion a series of chemical reactions so damaging that they can result in brain cell death. MAPK signaling pathways inside brain cells are thought to play a critical role in neurodegenerative diseases. Another important cell signaling pathway beneficially affected by EGCG, the PKC pathway, is also thought to play an essential role in the regulation of cell survival and programmed cell death.
Although no human studies on Alzheimer's disease have yet reported benefit from tea consumption, recent population studies have shown that simply consuming 2 or more cups of green tea daily reduces risk of cognitive decline and Parkinson's disease.
Green Tea Keeps Elders Mentally Sharp: Research Showing Multiple Ways
Green tea helps slow the age-related decline in brain function seen as declining memory, cognitive impairment, dementia and Alzheimer's, shows a human study published in the February 2006 issue of the American Journal of Clinical Nutrition.
Researchers at Japan's Tohoku University studied 1003 subjects over age 70, comparing their green tea intake and mental sharpness, using a Mini-Mental State Examination, a well-accepted standardized test for measuring cognitive function.
Drinking more than 2 cups a day of green tea slashed odds of cognitive impairment in elderly Japanese men and women by 64%! And a Japanese cup of green tea is much smaller than its American counterpart—only about 3.2 fluid ounces.
And at every level of cognitive impairment—from minimal to severe—those drinking the most green tea experienced significantly less mental decline than those drinking the least:
Compared with elderly Japanese who drank less than 3 cups a week, those drinking more than 2 cups a day had a 54% lower risk of age-related declines in memory, orientation, ability to follow commands and attention.
Those drinking 4 to 6 cups of green tea a week (1 cup a day) had a 38 lower risk of declines in brain function.
Green tea's primary protective agent is thought to be its catechin phytonutrient epigallocatechingallate or EGCG. Research shows this highly potent antioxidant:
helps prevent the formation of B-amyloid, a protein whose accumulation is recognized as causing Alzheimer's (Basianetto S, Eur J Neurosci Jan 2006).
protects brain cells by chelating (removing) iron, which might otherwise produce destructive free radicals (Reznichenko L, J Neurochem, March 2006).
helps prevent oxidative stress-induced brain cell death by "talking" to brain cells' genes responsible for cell cycling and survival. Specifically, EGCG tells the genes in neurons to decrease production of caspase 3, an enzyme involved in initiating programmed cell death. (Park HJ, Life Sci Jan 2006; Levites Y. J Biol Chem, 2002)
promotes memory-related learning ability by protecting cells in the hippocampus, a part of the brain involved in spatial cognition and memory-related learning ability, from free radical damage (Haque AM, J Nutr April 2006).
Green Tea Fights the Flu
A cup of green tea may help prevent or lessen the duration of the flu. In a lab study, published in the November 2005 issue of Antiviral Research, EGCG dramatically inhibited influenza virus replication in cell culture in all the subtypes of influenza virus tested. EGCG appears to suppress viral RNA synthesis by altering the properties of the viral membrane.
Pepper increases EGCG availability
An animal study suggests that consuming the spice, black pepper, when drinking green tea can significantly increase the amount of epigallocatechin-3-gallate (EGCG) absorbed. In this study, rats and mice given green tea along with piperine (a bioactive component in black pepper) absorbed 130% more EGCG than control animals receiving EGCG alone.
In this study, piperine was found to inhibit the glucuronidation of EGCG in the intestines. Glucuronidation is a chemical pathway that serves as one of the major ways our bodies convert drugs, steroids, and many other substances into metabolites that can then be excreted into the urine or bile. By inhibiting EGCG's glucuronidation, piperine allowed more of this catechin to be absorbed and utilized. So, next time you have a cup of green tea along with a meal, be sure to spice up your soup, salad and/or entrée with a little freshly ground black pepper.
Description
An oriental evergreen tree that can reach a height of 30 feet in the wild, the tea plant is kept as a shrub on tea plantations, where it is pruned to a height of about 3 feet to encourage new growth. A relative of the camellia with the botanical name of Camellia sinesis, the tea plant produces abundant foliage, a camellialike flower and berries containing one to two seeds. Only the smallest, youngest parts of the plant&mdah;the two leaves and bud at the tip of each new shoot—are picked for tea.
History
The tea plant, source of the most popular beverage in the world, is believed to have originated in the landmass encompassing Tibet, western China, and northern India. According to ancient Chinese legend, tea was discovered by the Chinese emperor Shen-Nung in 2737 B.C., when leaves from a wild tea bush accidentally fell into a pot of water he was boiling. The first recorded mention of tea appears in a contract for slaves known as "Tan Yuch," written by Wang Pao, poet laureate to Emperor Husan, in 59 B.C. By 780 A.D., when Lu Yu's The Classic of Tea was published in China, the cultivation and consumption of tea, whose name derives from the Chinese Amoy dialect word "t'e," pronounced "tay," had developed into a fine art. Today, "cha" means tea in Chinese. As this word moved westward into Middle Eastern languages, it sometimes became altered to “chai.”
India attributes the discovery of tea to the Buddhist monk Siddhartha in the 6th century. Legend has it that the prince-turned-monk traveled north from India to China to preach Buddhism, vowing he would meditate without sleeping for nine years. Reaching Canton in 519 A.D., he stationed himself before a wall of meditation where, after a mere five years, he was overcome by drowsiness. Inspired by divine intervention, he picked and chewed the leaves of a nearby tree, discovering, to his delight, a great sense of alertness and well-being. The tree whose health-giving properties enabled him to keep his vow was, of course, Camellia sinesis, whose leaves and seeds he carried with him as he continued his journey into Japan. In Japan, Buddhist monks quickly embraced tea, using it to remain alert during their own meditations and creating a simple drinking ritual that several hundred years later, tea master Sen-no Rikyu (1521-1591) developed into the high art of chanoyu, the Japanese tea ceremony.
From Japan, where tea was widely cultivated and consumed by the 9th century A.D., tea culture spread to Java, the Dutch East Indies, and other tropical and subtropical areas. In the 16th century, traders from Europe sailing to and from the Far East introduced Europeans to the delicious Asian drink, and by the 18th century, tea had become the national beverage of England.
Thousands of Chinese bushes stealthily acquired by botanist Robert Fortune, a "spy" for Great Britain's East India Trading Company, were introduced into India in the 1840s, where they quickly became a popular and profitable crop for the Empire.
Tea crossed the Atlantic with the American colonists, among whom its popularity led to the British imposition in 1767 of a tea tax that so infuriated the colonists that they revolted, tossing tons of tea into the harbor in 1733 in what became known as the Boston Tea Party. Freedom from unfair British taxation, symbolized by the tax on tea, became a central contributing factor to the Revolutionary War. The type of tea tossed into Boston harbor? Probably green since it was likely "gunpowder tea," green tea rolled tightly into pellets that looked like gunpowder shot to preserve its freshness during long voyages.
Several new innovations in tea consumption originated in the United States. In 1904, when a New York City merchant, Thomas Sullivan, sent his customers samples of tea in small silk bags, they found the bags could be used to conveniently brew a single cup of tea, and the tea bag was born. Another American innovation in tea drinking, instant tea, was first marketed in 1948.
Today, not China but India ranks as the number one producer of tea, although Sri Lanka (formerly Ceylon) is the major tea supplier to the U.S. Worldwide, more than 2.5 million metric tons of tea are produced each year with India, China, Sri Lanka, Kenya, Indonesia, Turkey, U.S.S.R, Japan, Iran and Bangladesh being the leading tea growing countries.
How to Select and Store
Whenever possible, ask for a sample of prepared tea before buying. Most high-quality teas will produce a pale green to yellow-green cup.
Loose Tea
To test for freshness, tightly squeeze a small amount and smell the aroma. The freshest, most flavorful tea will smell sweet and grassy.
Tea Bags
To test tea bags for freshness, remove the tea from one bag, place the empty bag in a cup, pour hot water over it., and let it steep for 2-3 minutes. If the result takes like plain hot water, the tea itself is likely fresh. If the tea bag water tastes like tea, the tea is old, and the paper has absorbed its flavor.
Since a single ounce of tea should produce 15 to 30 cups, the best way to ensure your tea is fresh is to purchase it in small amounts—two to four ounces at most. To retain freshness and flavor in both loose and bagged tea, store it in a tightly constructed opaque container to protect it from light, moisture and food odors.
Dark glass or ceramic containers are best; tins often leak as their seams are soldered. Use a small container just large enough to accommodate the amount of tea; tea exposed to the air in a half-empty large container will continue to oxidize.
It's best to store tea in a dark, cool, dry cupboard. Tea stored in the refrigerator is vulnerable to moisture and odors from other foods, and the water condensation that occurs when frozen tea is defrosted can ruin it.
The following are just a few delicious green teas available in most serious tea shops, mail-order catalogues and on-line sources of fine green teas:
Chinese Green Teas
The best Chinese green teas are thought to be those picked in early spring at the time of the Qing Ming festival, which takes place on April 5th of the solar calendar. These include:
After the Snow Sprouting: among the first tender sprouts available after the winter snows, these leaves produce a delicate tea with a fresh green scent.
Ching Ca: grown in mainland China, these teas include the famous Pi Lo Chun and Tai Ping Hou Gui.
Chun Mei (Precious Eyebrows): a name reflecting the fact that these springtime leaves are twisted into small curved shapes like lovely eyebrows. This high-grown tea from Yunnan province should be brewed lightly to produce an amber liquid with a wonderful aftertaste reminiscent of plums.
Dragonwell: with a fresh green taste, this is the favorite green tea of mainland China. The highest grade of this tea, Qing Ming, is named for the opening spring festival when the finest teas are picked.
Green Pearls: each pearl unfurls into three or four leaves that yield a lovely golden aromatic brew.
Gunpowder: a combination of buds and young green leaves rolled into balls reminiscent of gunpowder shot (hence its name), these also unfurl when infused. To test the freshness of gunpowder tea, pinch or squeeze a pellet. If fresh, it will resist; if stale, it will crumble. Two excellent gunpowder teas with a sweet, grassy taste are Gunpowder Pinhead Temple of Heaven and Gunpowder Temple of Heaven.
Guzhang Maohan (Mao Jin): these tea leaves from the Yellow Mountains of Anhui province produce a darker brew with a sweet, smoky flavor.
Pan Long Yin Hao: from Zhejiang province, this tea, a repeat winner in tea competitions conducted by the Chinese Ministry of Agriculture, is described as "a complex brew of multiple flavor notes."
Po Lo Chun: which translates to "Astounding Fragrance," aptly describes this slightly sweet yellowish tea with a lovely aftertaste.
Snow Dragon: grown near the border between Fujian and Zhejiang province, this tea is roasted in a large wok to produce a nutty, sweet flavor. Yunnan Green Needle: a pleasantly astringent clean-tasting tea made from delicate green buds.
Organic Green Teas
The most stringent standards for organic produce are found in California, Japan and Germany. Any tea that meets these standards is a high quality organic product.
The two most respected organic tea farms are in India: the Oothu Tea Estate, the first organic tea farm in the world, and Makaibari Tea Estates, which follows Rudolph Steiner's principles of harmony with nature through organic, sustainable methods of agriculture.
Indian Green Teas
Although green teas are a very small part of overall tea production in India, the following are notable.
Bherjan Estate: an organic green tea grown in Assam, India's most plentiful tea district. Assam teas are renowned for their hearty taste and "strength" in aroma and body.
Ambootia Tea Estate: a Darjeeling district organic green tea that produces a light, fragrant cup.
Makaibari Tea Estates: a multiple award winning Darjeeling green tea, flavorful but light.
Craigmore Estate: grown at high altitutes in the spectacular range of the Nilgiris, India's Blue Mountains, these green teas are exceptionally fragrant and sweet.
Japanese Green Teas
The best quality green teas are grown in the prefectures of Shizuoka and Uji.
Ban-cha: an earthy brown tea with an astringent taste made from roasted green tea leaves, bancha should only steep two to three minutes or it will become bitter.
Houjica: a lightly roasted bancha tea with a nutty flavor. A good nighttime choice as it is very light and low in caffeine.
Sen-cha: about 75% of the green tea harvested in Japan is Sencha, making it the most commonly consumed green tea in Japan. Sencha is especially rich in vitamin C and provides a clear rich yellow-green liquor that is grassy sweet and cleanly astringent. Made from a higher quality leaf than bancha or houjica, sencha is often called "guest tea." The most delightful sencha is Sencha Sakuro, a spring green tea scented with cherry blossoms. Another cherry-scented sencha to try is Spiderleg Sakuro whose longer, more "spidery" leaves produce a rich flavorful bouquet.
Gyokuro: the highest quality Japanese green tea, gyokuro has been called "history, philosophy and art in a single cup." For three weeks before the spring harvest, gyokuro leaves are shaded from direct sunlight, leading to a slower maturation that enhances the leaves' content of flavenols, amino acids, sugars and other substances that provide green tea's health benefits, aroma and taste. Intensely green and sweeter than sencha, gyokuro leaves can serve as the base for matcha—the silky chartreuse tea powder used to make chanoyu, the tea of the Japanese tea ceremony.
Mat-cha: Matcha differs from gyokuro in that the leaves are not rolled. After steaming, they are immediately and thoroughly dried, after which they are called tencha. Tencha is then ground into the superfine powder known as matcha. Use about two level teaspoons of matcha to ½ cup water and whip into a thick, invigorating brew, wonderful as an energizing morning tea or before exercise.
Shin-cha: In Japanese, "shin" means new and "cha" means tea. Shincha is literally "new tea" as it consists of leaves very lightly steamed immediately after harvesting. Shincha, which is only sold from May through July, is a highly aromatic tea with the aroma of freshly picked leaves. Because it is quite perishable, only a very small percentage of the tea harvest is processed as shincha; most of the leaves are used for sencha.
Genmai cha: Made from sencha mixed with genmai (puffed brown rice), this tea may be made from lower quality second harvest sencha but can also be found made from premium first-leaf sencha. The rice supplies a slightly nutty taste. Some tea retailers also add a pinch of matcha to the blend, giving it a vibrant green color.
How to Enjoy
Tips for Preparing
Green tea should be handled tenderly, just as you would fresh green leafy vegetables.
Spring water is the ideal choice for brewing tea, followed by filtered water. Distilled water should never be used; the brew it produces will be flat since the minerals removed from it are essential to bringing out tea's flavor.
To prepare the best loose tea, we recommend using a small food scale. Use three grams of tea to five ounces of water if brewing tea in a small teapot; four grams of tea to eight ounces of water for other methods.
As the size and shape of tea pots and cups varies considerably, it's a good idea to fill a measuring cup with 8 ounces of water and pour it into your tea pot or cup to determine how much water it really holds.
In making loose tea, remember that a teaspoon of small, dense leaves will weigh substantially more than a teaspoon of larger leaves, and the resulting tea will reflect this. A teaspoon of small dense leaves may be sufficient to produce a satisfying strong cup, while several teaspoons of larger leaves would be needed for a comparable brew.
Although heartily boiling water is used to brew black and oolong teas, green tea needs much lower temperatures (160-170 degrees F; 79-85 degrees C) and should be brewed for less time.
Let the water barely reach the boiling point to liberate its oxygen, then allow it to cool slightly before pouring over your tea. Until you are familiar with your tea kettle and the time it takes and sounds it makes when the correct temperature (170-185 degrees) has been reached, it's a good idea to check using a simple, inexpensive candy thermometer, available at any grocery store.
Brewing for 30 seconds to one minute is usually ideal; however, Nilgiri and Darjeeling greens can take several minutes, and Chinese Dragonwell teas are often best after 6-7 minutes of infusion.
Although good quality tea leaves will sink to the bottom after they have infused, it's a good idea to pour the tea over a small strainer if one is not built in to your teapot.
Quick Serving Ideas
Brew green tea with thinly sliced ginger and lemon, or sprigs of spearmint. Add one teaspoon of honey per cup, stir and serve hot or use half the amount of hot water (or twice the amount of tea), allow the tea to brew and cool, then pour over ice cubes.
Make a green tea chai by brewing green tea in hot vanilla soy milk and topping with a dash each of cinnamon, black pepper, ginger and allspice.
Brew 1-2 teaspoons loose leaf green tea in 8 ounces cool water for 20-30 minutes to develop flavor without bitterness and add to stir-fries, marinades, dressings, soups and sauces.
Sprinkle gyokuro tea over a salad, stew or rice dish.
Add ½ teaspoon gyokuro tea to an almost set omelet or scrambled eggs.
Add crushed gunpowder tea and rice vinegar to sesame oil for a delicious vinaigrette.
Mix gyokuro tea with sesame seeds and sea salt and use to dredge shrimp or fish filets before lightly pan-frying them.
Cook Japanese udon noodles in green tea for about 5 minutes, then remove from heat and leave noodles in tea until cool. Drain and toss lightly with soy sauce and sesame oil. Add thinly sliced tofu, scallions, mushrooms, and chopped cilantro, and serve.
Poach Asian or Bosc pears in green tea with fresh thinly sliced gingerroot. Drizzle with honey and top with a sprig of fresh mint.
Combine cooled green tea half and half with a fruit juice, such as peach, pineapple or papaya. Sweeten with a teaspoon of honey per cup. Blend and pour over ice.
Safety
Green Tea and Caffeine
Green tea contains caffeine, although half that found in coffee. The amount of caffeine that ends up in your cup of green tea will vary according to the amount of tea used, the length of time the leaves are infused, and if you drink the first or second infusion. Most of the caffeine in green tea is extracted into the water the first time the tea is infused.The table below compares the average amount of caffeine found in tea, other caffeinated drinks and chocolate.
There is limited research in the published literature comparing the caffeine content of green vs black tea. A recent study1 measured the caffeine content in the dry matter of the tea leaves, an approach that allows for control of any confounding variables related to preparation techniques that may impact the caffeine content in the final tea product. This study found that the caffeine content of one gram of black tea ranged from 22-28 milligrams while the caffeine content of one gram of green tea ranged from 11-20 milligrams, reflecting a significant difference. (Please note that not all of the caffeine from the tea leaves is extracted into the tea beverage, so these numbers only provide a relative level of caffeine difference between black and green tea, and not a reflection on the absolute amount contained in each tea beverage.)
Caffeine-containing Product Type of Product Caffeine (mg/serving)
Tea Green, black, oolong 50mg/190ml serving2
Green (different varieties) 20-45mg/8oz serving3
Black 47mg/8oz serving4
Coffee Brewed (filter or percolated) 100-115mg/190ml serving2
Instant 75mg/190ml serving2
Cola drinks Standard and Sugar Free 11-70mg/330ml can5
'Energy drinks' All types 28-87mg/250ml serving5
Chocolate Bar 5.5-35.5mg/50g bar5
1. Khokhar S, Magnusdottir SG. Total phenol, catechin, and caffeine contents of teas commonly consumed in the United kingdom. J Agric Food Chem. 2002 Jan 30;50(3):565-70.
2.Gray J (1998). Caffeine, coffee and health. Nutrition and Food Science 6:314-319.
3. Unpublished data
4. USDA National Nutrient Database for Standard Reference, Release 17 (2004)
5. Ministry of Agriculture, Fisheries and Food (MAFF) (1998). Survey of caffeine and other methylxanthines in energy drinks and other caffeine containing products (updated). Food Surveillance Information Sheet No. 144 (No. 103 revised). London.
Source: Tea Council Fact Sheet, http://www.teacouncil.co.uk/
What is a safe intake of caffeine?
The safety of caffeine consumption remains a topic of major debate in the research literature. To our knowledge, no studies have shown problems with caffeine consumption of less than 75 milligrams per day. Most studies showing potentially problematic effects of caffeine consumption have focused on intakes above 200 milligrams. In addition, there appears to be a significant difference in people’s sensitivity to caffeine. People sensitive to caffeine may wish to drink a decaffeinated green tea or, since approximately 80% of the caffeine is released in the first infusion, simply infuse the tea for 45 seconds in hot water, then pour off the liquid. Add more hot water and steep again. This method removes most of the tea's caffeine but little of its flavor and aroma.
At least two beneficial components in green tea—its catechins and the amino acid L-theanine—lessen the impact of its caffeine. When green tea is brewed, its caffeine combines with catechins in the water, reducing the caffeine's activity compared to coffee or cocoa. In addition, L-theanine, which is only found in tea plants and some mushrooms, directly stimulates the production of alpha brain waves, calming the body while promoting a state of relaxed awareness.
Green Tea and Drug Interactions
The tannins in green tea may decrease the absorption and thus the activity of the following drugs: atropine, Cardec DM®, codeine, ephedrine and pseudoephedrine, Lomotil®, Lonox®, theoplylline, aminophylline, and warfarin.
The caffeine in green tea may interact with the following drugs heightening their effects to dangerous levels: ephedrine and pseudoephedrine, theophylline, aminophylline.
Green Tea and Iron Absorption
Due to their high tannin-content, teas, including green tea, have been shown to prevent iron absorption. While this effect is helpful in persons with too much iron, consuming several cups of green tea daily may not be a good idea for persons deficient in iron or susceptible to iron deficiency.
Limit Green Tea Consumption During the First Trimester of Pregnancy
According to a study published in the March 2005 issue of Cancer Research, ECGC, a catechin present in green tea in amounts about 5 times higher than in black tea, inhibits the enzyme dihydrofolate reductase (DHFR), which cancer cells need to be able to grow, and which is a well recognized target of anti-cancer drugs.
Scientists decided to look at ECGC after they realized the green tea catechin looks a lot like the cancer drug methotrexate, which prevents cancer cells from making DNA by inhibiting the DHFR enzyme. They discovered that ECGC kills cancer cells in the same way as the drug.
Although ECGC binds strongly to DHFR, which is essential in both healthy and cancerous cells, it does not bind as tightly as methotrexate, so its side effects on healthy cells are less severe than those of the drug.
ECGC's binding to DHFR may also explain why women who drink large amounts of green tea around the time they conceive and early in their pregnancy may have an increased risk of having a child with spina bifida or other neural tube disorders.
Women are advised to take supplements of folic acid when trying to conceive and during the first trimester (the first 3 months) of pregnancy because it is during this time period that the baby's neural tube is developing. Folic acid helps ensure normal development and protects against spina bifida by enabling the production of the enzyme DHFR. While a cup or two of green tea is unlikely to pose a problem, drinking large amounts of green tea could decrease the activity of DHFR, increasing risk of neural tube defects.
Nutritional Profile
Introduction to Food Rating System Chart
The following chart shows the nutrients for which this food is either an excellent, very good or good source. Next to the nutrient name you will find the following information: the amount of the nutrient that is included in the noted serving of this food; the %Daily Value (DV) that that amount represents (similar to other information presented in the website, this DV is calculated for 25-50 year old healthy woman); the nutrient density rating; and, the food's World's Healthiest Foods Rating. Underneath the chart is a table that summarizes how the ratings were devised. For more detailed information on our Food and Recipe Rating System, please click here.
Green tea
0.07 ounces
0.00 calories
Nutrient Amount DV
(%) Nutrient
Density World's Healthiest
Foods Rating
World's Healthiest
Foods Rating Rule
excellent DV>=75% OR Density>=7.6 AND DV>=10%
very good DV>=50% OR Density>=3.4 AND DV>=5%
good DV>=25% OR Density>=1.5 AND DV>=2.5%
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This page was updated on: 2006-05-07 15:00:18
© 2002 The George Mateljan Foundation
Green tea
All true teas—as distinct from herbal and flower infusions, which afficiandos call tisanes—are made from the leaves of a magnolia-related evergreen tree with the botanical name of Camellia sinensis. Although reaching a height of 30 feet in the wild, on tea plantations (called gardens or estates), the plant is kept as a shrub, constantly pruned to a height of about 3 feet to encourage new growth and for convenient picking.
Tea plants grow only in warm climates but can flourish at altitudes ranging from sea level to 7,000 feet. The best teas, however, are produced by plants grown at higher altitudes where the leaves mature more slowly and yield a richer flavor. Depending upon the altitude, a new tea plant may take from 2 ½ to 5 years to be ready for commercial picking, but once productive, it can provide tea leaves for close to a century.
Tea plants produce abundant foliage, a camellia-like flower, and a berry, but only the smallest and youngest leaves are picked for tea—the two leaves and bud at the top of each young shoot. The growth of new shoots, called a flush, can occur every week at lower altitudes but takes several weeks at higher ones. The new leaves are picked by hand by "tea pluckers," the best of whom can harvest 40 pounds per day, enough to make 10 pounds of tea.
All tea plants belong to the same species—Camellia sinensis—, but local growing conditions (altitude, climate, soils, etc.) vary, resulting in a multitude of distinctive leaves. The way the leaves are processed, however, is even more important in developing the individual characteristics of the three predominant types of tea: green, black and oolong.
Green tea is the least processed and thus provides the most antioxidant polyphenols, notably a catechin called epigallocatechin-3-gallate (EGCG), which is believed to be responsible for most of the health benefits linked to green tea. Green tea is made by briefly steaming the just harvested leaves, rendering them soft and pliable and preventing them from fermenting or changing color. After steaming, the leaves are rolled, then spread out and "fired" (dried with hot air or pan-fried in a wok) until they are crisp. The resulting greenish-yellow tea has a green, slightly astringent flavor close to the taste of the fresh leaf.
In black tea production, the leaves are first spread on withering racks and air-blown, which removes about one-third of their moisture and renders them soft and pliable. Next, they are rolled to break their cell walls, releasing the juices essential to fermentation. Once again, they are spread out and kept under high humidity to promote fermentation, which turns the leaves a dark coppery color and develops black tea's authoritative flavor. Finally, the leaves are "fired," producing a brownish black tea whose immersion in hot water gives a reddish-brown brew with a stronger flavor than green or oolong teas.
Oolong tea, which is made from leaves that are partially fermented before being fired, falls midway between green and black teas. Oolong is a greenish-brown tea whose flavor, color and aroma are richer than that of green tea, but more delicate than that of black.
Green tea has always been, and remains today, the most popular type of tea from China where most historians and botanists believe the tea plant originated throughout all of Asia. Why is this so? Perhaps because green tea not only captures the taste, aroma and color of spring, but delivers this delightful bouquet along with the highest concentration of beneficial phytonutrients and the least caffeine of all the teas.
Health Benefits
Description
History
How to Select and Store
How to Enjoy
Safety
Nutritional Profile
References
Health Benefits
Green tea is particularly rich in health-promoting flavonoids (which account for 30% of the dry weight of a leaf), including catechins and their derivatives. The most abundant catechin in green tea is epigallocatechin-3-gallate (EGCG), which is thought to play a pivotal role in the green tea's anticancer and antioxidant effects. Catechins have been found to be more potent free radical scavengers than the well known antioxidants vitamins E and C.
Most of the research showing the health benefits of green tea is based on the amount of green tea typically consumed in Asian countries—about 3 cups per day (which would provide 240–320 mg of polyphenols). Just one cup of green tea supplies 20-35 mg of EGCG, which has the highest antioxidant activity of all the green tea catechins.
The health benefits of green tea have been extensively researched and, as the scientific community's awareness of its potential benefits has increased, so have the number of new studies. As of November 2004, the PubMed database contained more than 1,000 studies on green tea, with more than 400 published in 2004! Following is a brief summary of some of the high points of this most current research.
Green tea drinkers appear to have lower risk for a wide range of diseases, from simple bacterial or viral infections to chronic degenerative conditions including cardiovascular disease, cancer, stroke, periodontal disease, and osteoporosis. The latest studies provide a deeper understanding of the ways in which green tea:
Protects against Coronary Artery Disease
In Japanese studies, green tea consumption has been found to be an independent predictor for risk of coronary artery disease. In one study, those drinking 5 or more cups of green tea each day were found to be 16% less likely to suffer from coronary artery disease. The relationship was so significant researchers concluded, "The more green tea patients consume the less likely they are to have coronary artery disease."
An elevation in the amount of free radicals in the arteries is a key event in many forms of cardiovascular disease. The latest research shows that green tea catechins inhibit the enzymes involved in the production of free radicals in the endothelial lining of the arteries. The arterial endothelium is a one-cell thick lining that serves as the interface between the bloodstream and the wall of the artery where plaques can form. By protecting the endothelium from free radical damage, green tea catechins help prevent the development of cardiovascular disease.
Inhibits Atherosclerosis
Green tea has been shown to effectively lower risk of atherosclerosis by lowering LDL cholesterol, triglycerides, lipid peroxides (free radicals that damage LDL cholesterol and other lipids or fats) and fibrinogen (a protein in the blood involved in the formation of blood clots), while improving the ratio of LDL (bad) to HDL (good) cholesterol. In animal studies in which green tea was given in human equivalent doses to hamsters, atherosclerosis was inhibited 26-46% in those receiving the lower dose (equivalent in humans to 3-4 cups per day) , and 48-63% in those receiving the higher dose (10 cups a day in humans).
Special Benefits for Persons with High Triglycerides
Green tea may offer special heart-protective benefits for persons with high triglycerides, suggests a laboratory study, published in the February 2005 issue of the Journal of Nutrition.
A series of experiments revealed that the mix of catechins naturally found in green tea dose-dependently inhibit the activity of pancreatic lipase, the enzyme secreted by the pancreas that digests fat. As a result, the rate at which the body breaks down of fats into triglycerides, and the rise of triglyceride levels in the bloodstream that occurs after meals, is greatly slowed. Since a large rise in blood levels of triglycerides after a meal is a significant risk factor for coronary heart disease, drinking a cup of two green tea along with your meals is a good idea, especially if your triglyceride levels are higher than normal.
Thins the Blood and Helps Prevent Blood Clots
Green tea catechins help thin the blood and prevent the formation of blood clots by preventing the formation of pro-inflammatory compounds derived from omega-6 fatty acids, which are found in meats and polyunsaturated vegetable oils such as corn, safflower and soy oil. These pro-inflammatory compounds—specifically, arachidonic acid from which the inflammatory cytokines thromboxane A2 and prostaglandin D2 are derived—cause platelets to clump together.
Protects the Heart in Patients with Acute Cardiovascular Disease
The primary catechin in green tea, EGCG (epigallocatechin-3-gallate) confers such powerful protection that it can help prevent the death of heart muscle cells following ischemia/reperfusion injury. Ischemia is the medical term for a restriction in blood supply and therefore in oxygen and nutrients. When circulation is restored, oxidative damage occurs, and this is referred to as reperfusion injury. EGCG prevents heart muscle damage by blocking the activation of inflammation-related compounds (including NF-kappa-B and STAT-1) that play a critical role in promoting the oxidative damage that kills heart cells in reperfusion injury. Researchers believe EGCG can be used to help minimize damage in patients with acute coronary artery disease.
Minimizes Damage and Speeds Recovery after a Heart Attack
Research conducted over the last several years by Dr. Anastasis Stephanou and his team at the UK's Institute of Child Health and published in the FASEB Journal, the journal of the Federation of Experimental Biology and the Journal of Cellular and Molecular Medicine has focused on EGCG's ability to block the action of the protein, STAT-1. Normally activated in cells after a heart attack or stroke, STAT-1 plays a major role in inducing cell death.
Not only does green tea minimize heart cell death after a heart attack or stroke, ECGC also appears to speed up heart cells' recovery from damage, allowing the tissues to recover more quickly and alleviating damage to organs. Dr. Stephanou, a molecular biologist, noted: "We're extremely encouraged by these findings and hope to implement them in the clinical setting to minimize cell death activation in patients with acute coronary heart disease."
Minimizes Damage to the Brain after a Stroke
EGCG has also been shown to protect brain cells by these same mechanisms and thus may help minimize the brain damage that occurs after a stroke. In one animal study, green tea was so effective in reducing the formation of free radicals in brain tissue that the researchers concluded, "Daily intake of green tea catechins efficiently protects the brain from irreversible damage due to cerebral ischemia, and consequent neurologic deficits."
Lowers Blood Pressure and Helps Prevent Hypertension
A study published in the July 2004 issue of the Archives of Internal Medicine found that among persons consuming tea regularly for at least one year, the risk of developing high blood pressure was 46% lower among those who drank ½ cup to 2 ½ cups per day, and 65% less among those consuming more than 2 ½ cups per day.
In another study, this one of rats bred not only have high blood pressure but also to be prone to strokes, those rats given green tea had significantly lower systolic and diastolic blood pressure compared to controls, who received plain water. The animals in this study, which was published in the January 2004 issue of the Journal of Nutrition, consumed the human equivalent of 1 liter (1.1 quarts or a little more than 4 cups) of green tea per day.
Helps Prevent the Development of Atherosclerosis and Cancer
In both atherosclerosis and cancer, cell growth and proliferation is central to the disease process. In atherosclerosis, plaques form in the lining of the arteries, which grow thicker and less elastic, impeding blood flow. In cancer, normal brakes on cells turn off, and they multiply out of control. Green tea can help stop abnormal cell proliferation.
Catechins, among the main active compounds in green tea leaves, shut down the primary relay station through which growth factors central to both atherosclerosis and cancer send their messages for growth. These relay stations, called tyrosine kinase receptors, are essential for the transmission of messages sent by platelet derived growth factor, insulin-like growth factor, epidermal growth factor, fibroblast growth factor, and vascular endothelial growth factor. The result is the prevention of or halting of the disease processes that depend upon excessive cellular growth.
Two other damaging factors that cause the cells lining our vasculature to proliferate are AGEs (advanced glycation end products) and MAPK (mitogen-activated protein kinase). AGEs form when sugars inappropriately bind to and distort proteins. MAPK activity is normally enhanced in the presence of elevated levels of LDL cholesterol. In laboratory studies, green tea polyphenols were shown to dose-dependently inhibit AGE-stimulated proliferation of vascular smooth muscle cells and to prevent the increase in MAPK normally seen when LDL levels are high.
Protects against Cancer
In the last ten years, green tea's cancer-preventive effects have been widely supported by epidemiological, cell culture, animal and clinical studies. For cancer prevention, the evidence is so overwhelming that the Chemoprevention Branch of the National Cancer Institute has initiated a plan for developing tea compounds as cancer-chemopreventive agents in human trials.
When confronted with a cancerous cell, green tea becomes the plant kingdom's Arnold Schwarzenegger, helping to terminate cancer cells in a remarkable number of ways.
Laboratory cell culture studies show that green tea polyphenols are powerful triggers of apoptosis (cell suicide) and cell cycle arrest in cancerous but not in normal cells. (Cell cycling is the process cells go through to divide and replicate.)
These anticancer actions have been assumed to be due to the powerful antioxidant effects of green tea's catechins, especially epigallocatechin-3-gallate (EGCG). This is a reasonable assumption, given that a number of studies have shown that green tea possesses remarkable antioxidant properties. In one study published in the November 2004 issue of Mutation Research, EGCG's protective antioxidant effects against several carcinogens were found to be 120% stronger than those of vitamin C.
But while green tea's antioxidant prowess is impressive, recent studies show it is far from the only way in which this multi-talented beverage protects us against cancer.
One of these mechanisms is green tea's ability to inhibit angiogenesis, the development of new blood vessels. Cancer cells, which are constantly attempting to divide and spread, have an endless appetite that can only be temporarily quieted by increasing the number of blood vessels that supply them with nutrients. By inhibiting angiogenesis, green tea helps starve cancer.
Studies also show that green tea works at the genetic level, shutting off genes in cancerous cells that are involved in cell growth, while turning on those that instruct the cancer cells to self-destruct. EGCG has even been found to work as a pro-oxidant or free radical, but just inside cancer cells, where it causes so much damage that the cancer cells' self-destruct mechanisms are triggered.
A study of ECGC's effects on keratinocytes (the major type of epidermal or skin cell) found that this green tea compound has yet another means of correcting cancer—that of turning on the genes that direct the cancer cell to return to normal.
Green tea's anticancer effects include its ability to inhibit the overproduction of the enzyme cyclooxygenase (COX)-2, a protein whose overproduction has been implicated as a factor in many diseases, including arthritis and cancer. COX-2 has an enzyme counterpart, called COX-1, which may be helpful to leave untouched when preventing overproduction of COX-2. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin and ibuprofen (which inhibit both COX-1 as well as COX-2), and specific COX-2 inhibitors such as Vioxx and Celebrex (which inhibit only COX-2), have been considered as possible agents in the prevention of some forms of cancer, but their severe toxic side effects on normal cells limit their usefulness. In studies of prostate cancer cells, EGCG appears to block only COX-2 and to have no negative side effects.
Prostate Cancer
EGCG provides other benefits specific to prostate cancer prevention. A study published in the December 2004 issue of the International Journal of Cancer found that EGCG significantly inhibited, in a dose-dependent manner, the production of prostate-specific antigen (PSA), a marker for prostate cancer risk. Not only did EGCG lower PSA levels, but it also suppressed all the activities of PSA which were examined that promote prostate cancer.
Green tea polyphenols halt prostate cancer at multiple levels
The polyphenols in green tea help prevent the spread of prostate cancer by mobilizing several molecular pathways that shut down the proliferation and spread of tumor cells, while also inhibiting the growth of blood vessels that supply the cancer with nourishment, according to research published in the December 2004 issue of Cancer Research.
Green tea polyphenols:
decrease insulin-like growth factor-1 (IGF-1), while increasing levels of IGF binding protein-3, which binds IGF-1, further diminishing its activity. (Increased levels of IGF-1 are associated not only with prostate cancer, but cancers of the breast, lung and colon.)
inhibit key cell survival proteins, promoting apoptosis or programmed cell death in cancer cells.
reduce the expression of several compounds (urokinase plasminogen activator and matrix metalloproteinase 2 and 9) involved in the metastasis and spread of cancer cells.
reduce the amount of vascular endothelial growth factor (VEGF), which develops new blood vessels to carry nutrients to developing tumors.
All these effects were seen in this animal study within 6 months of continuous infusion. While obviously impractical for humans, the study suggests that daily consumption of green tea may be highly protective.
Ovarian Cancer
Green tea consumption has been shown to enhance survival in women with ovarian cancer. In a study published in the November 2004 issue of the International Journal of Cancer, women with ovarian cancer who drank at least 1 cup of green tea daily had a 56% lowered risk of death during the 3 years of the study compared to non-tea drinkers. A laboratory study of human ovarian cancer cells published in the September 2004 issue of Gynecologic Oncology explains why: EGCG not only suppresses the growth of ovarian cancer cells, but also induces apoptosis (cell suicide) in these cells by affecting a number of genes and proteins.
An epidemiological (population) study published in the December 2005 issue of the Archives of Internal Medicine, adds more evidence that enjoying a cup or two of tea each day may significantly lower a woman's risk of ovarian cancer.
Data from numerous other studies has suggested that both green and black tea may offer protection against various cancers, with tea polyphenols thought to be the most likely protective agents. In this research, Susanna Larsson and Alicja Wolk from the National Institute of Environmental Medicine, Stockholm, Sweden, decided to look specifically at the relationship between tea consumption and ovarian cancer.
Participants in their study were 61,057 Swedish women aged 40-76 years who were in the Swedish mammography cohort and had completed a validated 67 item food frequency questionnaire at baseline (between 1987-1990), after which the women were followed an average of 15.1 years.
Analysis of the data found that even women who averaged less than one cup of tea per day had an 18% lower risk of ovarian cancer than non-tea-drinkers.
Those who drank one cup per day had a 24% lower risk, and those who drank two or more cups of tea per day had a 46% lower risk of ovarian cancer than non-tea-drinkers.
Each additional cup of tea per day was associated with an 18% lower risk of ovarian cancer. Although higher tea consumption was generally associated with other health-promoting behaviors, including higher consumption of fruits and vegetables, when compared to the lifestyle behaviors of those who seldom or never drank tea, the large drop in ovarian cancer risk seen as tea consumption increased does suggest that tea is likely to offer significant protection.
Breast Cancer
Recent studies have also identified two mechanisms through which green tea works against breast cancer. Not only does EGCG inhibit the activity of telomerase, an enzyme that plays a key role in cell division, in breast cancer cells, but it also offers help to women with estrogen-negative breast cancer, a form of breast cancer that is very hard to treat successfully.
Estrogen-negative breast cancer cells express high amounts of the epidermal growth factor Her-2/neu, while in the more treatable estrogen-positive form of breast cancer, estrogen-receptor alpha (ERalpha) is expressed. According to a study published in the October 2004 issue of Molecular and Cellular Biology, EGCG induces the expression of ERalpha rather than Her-2/neu in breast cancer cells.
Brain Tumors in Children
Green tea's ability to inhibit telomerase may also translate into help for children with the most common malignant brain tumors of childhood, primitive neuroectodermal tumors. Telomerase's activity allows cancer cells to avoid the normal limits on the number of times a cell can replicate before it self-destructs. In a study published in the January 2004 issue of Neuro-oncology, investigators found that telomerase activity was at least five times higher in children with these brain tumors than in normal brain cells and that EGCG strongly inhibited telomerase activity in a dose-dependent manner.
Colon Cancer
Green tea may also reduce the increased risk for colon cancer caused by a high fat diet. An animal study published in the journal Nutrition and Cancer in 2003 found that when green tea was given along with a diet high in omega 6 fat (in the form of corn oil), the amount of pro-inflammatory compounds produced in the colon (5-lipoxygenase, leukotriene A4 hydrolase, and leukotriene B4) was significantly lower, as was the resulting number of precancerous colon cells (aberrant crypt foci). Green tea consumption even reduced the amount of abdominal fat produced in the animals that received it compared to controls.
Lung Cancer
While we certainly do not recommend smoking, if you or someone you love smokes, or if you must be around smokers and are exposed to second hand smoke, drinking green tea can offer some protection against lung cancer. A human pilot study recently confirmed the protective effects of green tea against lung cancer seen in cell culture and animal studies. The study, published in the November 2004 issue of Molecular Nutrition and Food Research evaluated the effect of green tea (5 cups per day) on 3 heavy smokers (>10 cigarettes a day) and 3 individuals who had never smoked. When the study subjects were drinking green tea, DNA damage caused by smoking was decreased, cell growth was inhibited, and cellular triggers for apoptosis (cell suicide) in abnormal cells increased.
Another larger four month study of heavy smokers involving 100 women and 33 men found that levels of urinary 8-hydroxydeoxyguanosine, a marker of free radical damage to DNA, dropped significantly in individuals drinking decaffeinated green but not black tea. Decaffeinated green tea was especially effective in reducing DNA damage in individuals who lack the genetic ability to produce normal amounts of an enzyme called glutathione S-transferase, which plays a key role in the liver's ability to detoxify many of the carcinogens found in cigarette smoke. Individuals whose genetic inheritance does not include the GSTM1 and GSTT1 variants of the genes that instruct the cell to produce glutathione S-transferase are more susceptible to developing many different cancers. For these individuals, green tea may be especially beneficial.
Bladder Cancer
Research by a multi-departmental team from UCLA has produced valuable insights into how green tea extract might be capable of acting against the invasive growth of bladder cancer tumors. Green tea extract has been shown, via a mechanism that affects cell movement, to target cancer cells while leaving healthy cells alone.
For cancer to grow and spread, the malignant cells must be able to move, and their movement depends on a process called actin remodeling, which itself is carefully regulated by complex signaling pathways, including the Rho pathway.
By inducing Rho signaling, green tea causes cancer cells to mature more rapidly and to bind together more closely, a process called cell adhesion. Both their increased maturity and cell adhesion inhibit cancer cells' mobility, according to Rao, senior author of the study, published in the February 2005 issue of Clinical Cancer Research, in which green tea's effects on Rho signaling were noted.
"Cancer cells are invasive and green tea extract interrupts the invasive process of the cancer…In effect, the green tea extract may keep the cancer cells confined and localized, where they are easier to treat and the prognosis is better," explained Rao.
About 56,000 new cases of bladder cancer are diagnosed each year, making it the fifth most common cancer in the United States. About half of all bladder cancers are believed to be related to cigarette smoking. Bladder cancer can be difficult to detect in the early, most treatable stages, yet, when not found early, the tumors can be aggressive, and more than half of patients with advanced cancers experience recurrences. In the next phase of his research, Rao and his team will analyze urine from bladder patients, looking particularly for biomarkers associated with actin remodelling and the activation of the Rho pathway, to determine which subset of patients might benefit most from green tea.
Improves the Efficacy of Cancer Drugs While Lessening Their Negative Side-Effects
In the fight against cancer, green tea polyphenols are team players, helping cancer-killing drugs do their job. In a study published in the October 2004 issue of the Journal of Pharmacy and Pharmacology, green tea polyphenols caused drug-resistant cancer cells, which were able to extrude or push out one of the most commonly used cancer drugs, doxorubicin, to retain the drug, which could then destroy them. According to a study published in the August 2004 issue of Cancer Letters, another compound in green tea, the amino acid theanine, reduces the negative side effects of doxorubicin by increasing the level of one of the body's most important internally produced antioxidants, glutathione, in normal tissues in the liver and heart—but not in tumors.
Understanding How Green Tea Fights Cancer
Spanish and British scientists have discovered at least one of the mechanisms through which green tea helps to prevent certain types of cancer, according to a study published in the March 2005 issue of Cancer Research.
ECGC, a catechin present in green tea in amounts about 5 times higher than in black tea, inhibits the enzyme dihydrofolate reductase (DHFR), which cancer cells need to be able to grow, and which is a well recognized target of anti-cancer drugs.
Scientists decided to look at ECGC after they realized the green tea catechin looks a lot like the cancer drug methotrexate, which prevents cancer cells from making DNA by inhibiting the DHFR enzyme. They discovered that ECGC kills cancer cells in the same way as the drug.
Although ECGC binds strongly to DHFR, which is essential in both healthy and cancerous cells, it does not bind as tightly as methotrexate, so its side effects on healthy cells are less severe than those of the drug.
ECGC's binding to DHFR may also explain why women who drink large amounts of green tea around the time they conceive and early in their pregnancy may have an increased risk of having a child with spina bifida or other neural tube disorders.
Women are advised to take supplements of folic acid when trying to conceive and during the first trimester (the first 3 months) of pregnancy because it is during this time period that the baby's neural tube is developing. Folic acid helps ensure normal development and protects against spina bifida by enabling the production of the enzyme DHFR. While a cup or two of green tea is unlikely to pose a problem, drinking large amounts of green tea could decrease the activity of DHFR, increasing risk of neural tube defects.
Improves Insulin Sensitivity in Type 2 Diabetes
Population studies suggest that green tea consumption may help prevent type 2 diabetes. A number of animal studies are beginning to explain why. New studies suggest that green tea may improve glucose tolerance and insulin sensitivity in individuals with diabetes. In one study, after receiving green tea for 12 weeks, diabetic rats had lower fasting blood levels of glucose, insulin, triglycerides and free fatty acids compared to controls, and the ability of their adiopcytes (fat cells) to respond to insulin and absorb blood sugar greatly increased.
In another study by the same research group, diabetic rats were separated into three groups and followed for 12 weeks. One group was given with standard rat chow and water (the control group), the second group received a high fructose diet and water (fructose group), and the third group got the same high fructose diet and green tea (green tea group). By the end of the study, the fructose group had high blood sugar, high insulin levels, and high blood pressure, while the animals receiving green tea along with a high fructose diet showed improvement in all three.
A study published in the August 2004 issue of BMC Pharmacology, in which oral glucose tolerance tests were given to healthy humans after they consumed green tea, showed that it increased the body's ability to utilize blood sugar.
Another interesting animal study compared the effects of a Western diet, a vegetarian diet and a Japanese diet, each with or without green tea. Blood sugar concentrations were highest in the animals on the Western diet followed by the Vegetarian diet with the Japanese diet producing the lowest blood sugars. When supplemented with green tea, blood sugar levels dropped in rats on all three diets, with those on the Japanese diet having not only the lowest blood sugars but also rating the best on other risk factors for type 2 diabetes. Rats on the Japanese diet that also were given green tea had the lowest triglycerides and cholesterol as well as the highest ratio of beneficial omega-3 fatty acids to potentially inflammatory omega-6 fatty acids. The researchers concluded that Japanese eating habits combined with drinking green tea might help prevent type 2 diabetes.
One of the mechanisms through which green tea improves insulin sensitivity has recently been identified in laboratory studies that show that epigallocatechin 3-gallate (EGCG) does a good deal more to prevent type 2 diabetes than lower the production of free radicals. EGCG also works on the genetic level, causing a reduction in the number of messenger RNAs that direct liver cells to produce the enzymes involved in the creation of glucose (sugar).
Protects against Kidney Disease
An animal study published in the January 2005 issue of Pharmacological Research suggests yet another beneficial effect of green tea consumption: the prevention of kidney dysfunction in persons who must take powerful immunosuppressant drugs, for example, after an organ transplant.
One such drug, cyclosporine A, while a very effective immunosuppressant, also markedly elevates the production of free radicals highly toxic to the kidneys. In this study, rats given green tea as their drinking water along with cyclosporine A produced far fewer damaging free radicals than rats given plain water. In addition, a number of other indicators of kidney function (serum creatinine, blood urea nitrogen, uric acid and urinary excretion of glucose) were significantly better in rats given green tea.
Another animal study published in May 2004 in the Annals of Nutrition & Metabolism explains why. Diabetic rats given green tea catechins and then exposed to a kidney-damaging drug, streptozotocin, produced less than half the amount of superoxide radicals (a particularly damaging type of free radical) compared to diabetic rats on a catechin-free diet. As a result, a cellular waste product formed by free radical damage to fats, lipofuscin, was almost 200% higher in the diabetic rats who did not receive green tea catechins compared to those who did.
Prevents Osteoporosis and Periodontal diseases
Excessive bone loss is a characteristic feature not only of osteoporosis but of periodontal disease. Green tea supports healthy bones and teeth both by protecting osteoblasts (the cells responsible for building bone) from destruction by free radicals, and by inhibiting the formation of osteoclasts (the cells that break down bone).
Another benefit of green tea consumption for those with periodontal disease: green tea short circuits the damaging effects of the bacteria most responsible for gum disease, Porphyromonas gingivalis. P. gingivalis causes gum damage by producing toxic byproducts such as phenylacetic acid and by stimulating the activity and production of enzymes called metalloproteinases (MMPs), which destroy both the mineral and organic constituents that make up the matrix of our bones. Epigallocatechin-3-gallate (EGCG) inhibits P. gingivalis' production of both phenylacetic acid and MMPs.
Protects the Liver from Alcohol and Other Harmful Chemicals
Alcohol metabolism results in the production of damaging free radicals that can overwhelm the liver's supply of antioxidants, resulting in liver injury. In a study published in the January 2004 issue of Alcohol in which rats were chronically intoxicated with alcohol for 4 weeks, green tea prevented damage to their livers.
Other animal research shows that epigallocatechin-3-gallate (EGCG) protects the liver against the free radicals generated when mice are exposed to carbon tetrachloride, a toxic chemical solvent. Without the protection afforded by EGCG, carbon tetrachloride exposure resulted in the production of numerous free radicals that destroyed a significant amount of the animals' liver cells. With EGCG, free radical production and liver injury was so greatly reduced that researchers suggested green tea should be used in the treatment of liver disease.
Unlike some herbs, green tea's protective effects do not appear to affect two of the liver enzymes most often responsible for detoxifying and eliminating drugs, cytochrome P-450 2D6 and 3A4. This suggests that green tea might be safely consumed when taking medications primarily dependent upon the CYP2D6 or CYP3A4 pathways of metabolism. Hopefully, future research studies will bear out this potential benefit.
On the other hand, one study found that Japanese green tea did increase the activity of the CYP1A1 enzyme. Researchers hypothesized that the increase in activity of this liver enzyme may be one of the ways in which green tea helps protect against cancers caused by various dietary carcinogens.
Promotes Fat Loss
Green tea not only promotes fat loss, but specifically, the loss of visceral fat—fat that accumulates in the tissues lining the abdominal cavity and surrounding the intestines (viscera) and internal organs. Unlike fat deposits on the hips and thighs (which result in the so-called "pear" body shape), visceral fat (which produces the "apple" body shape) is highly associated with increased risk for metabolic syndrome and type 2 diabetes. Green tea contains three major components that promote fat loss: catechins, caffeine and theanine. Studies suggest that green tea compounds promote fat loss by inhibiting both gastric and pancreatic lipase, the enzymes that digest triglycerides, and fatty acid synthetase, the enzyme responsible for synthesizing fatty acids into the form in which they can be stored in the body's adipose (fat) cells.
In a study published in the January 2004 issue of In Vivo in which mice were fed diets containing 2% green tea powder for 16 weeks, visceral fat decreased by 76.8% in those receiving green tea compared to the control group. Green tea also decreased blood levels of triglycerides (the chemical form in which most fats exist in the body).
A human study, published in the January 2005 issue of the American Journal of Clinical Nutrition, confirms green tea's ability to not only reduce body fat, but damage to LDL cholesterol as well. After 12 weeks of drinking just one bottle of green tea each day, 38 normal-to-overweight men in Tokyo had a significantly lower body weight, BMI, waist circumference, body fat mass and amount of subcutaneous fat compared to men given a bottle of oolong tea each day.
After a 2 week diet run-in period, the men were divided into two groups, one of which drank a bottle of green tea containing 690 mg of catechins, while the other group drank a bottle of oolong tea containing 22 mg catechins.
Not only did the men drinking green tea lose weight and fat, but the amount of their LDL cholesterol damaged by free radicals also dropped significantly. Since atherosclerotic plaques develop when cholesterol circulating in the bloodstream is damaged or oxidized, green tea's ability to prevent these oxidation reactions may explain some of its protective effects against cardiovascular diseases.
Increases Exercise Endurance
Green tea extract given to lab rats over a 10-week span increased the amount of time the animals could swim before becoming exhausted by as much as 24%.
Green tea's catechins appear to stimulate the use of fatty acids by liver and muscle cells. In muscle cells, the ability to burn more fat translates into a reduction in the rate at which glycogen, the form in which carbohydrates are stored for ready access in muscle, is used up, thus allowing for longer exercise times. Green tea's effect on muscle cells' ability to take in and burn fatty acids, speeding up fat breakdown, is also thought to be the reason why it helps weight loss.
The idea for the experiment came from the fact that skeletal muscles utilize carbohydrates, lipids (fats) and amino acids (protein) as energy sources, but the ratio in which they are used varies with the intensity and type of the exercise, and the level of the individual's fitness. During endurance exercise, the use of too much carbohydrate is undesirable because it triggers insulin secretion, which, in turn, both inhibits the burning of fatty acids and stimulates lactic acid production. (Lactic acid buildup is what causes that sore achy feeling in your muscles when you exercise.) Conversely, enhanced availability and utilization of free fatty acids reduces carbohydrate utilization, which in turn spares glycogen (the form in which carbohydrates are stored in muscle for quick use) and suppresses lactic acid production, resulting in an increase in endurance."
Drinking a single cup of green tea before exercise, however, will not be effective. One single, higher "dose" of green tea did nothing to improve lab rats' performance. The animals had to receive green tea daily, and endurance increased gradually over the 10 weeks of the study. To match the beneficial effect on test animals' endurance capacity seen in the experiments, the researchers estimate a 165-pound athlete would need to drink about 4 cups of green tea daily.
Protects against Cognitive Decline, Alzheimer's Disease and Parkinson's Disease
Damage to brain cells in Parkinson's, Alzheimer's and other neurodegenerative diseases seems to result from the combination of a number of damaging factors including excessive inflammation and increased levels of iron, both of which lead to increased free radical production, exhaust the brain's supply of protective antioxidants and trigger the production of certain proteins, such as amyloid-beta, which promote apoptosis (cell suicide).
Green tea catechins, until recently thought to work simply as antioxidants, are now known to invoke a wide spectrum of neuroprotective cellular mechanisms. These include iron chelation, scavenging of free radicals, activation of survival genes and cell signaling pathways, and regulation of mitochondrial function. (The mitochondria are the energy production factories inside our cells. When they are not working properly, they generate many free radicals and little energy.) The end result is a significant lessening of damage to brain cells.
Iron accumulation in specific brain areas and free radical damage to brain cells are considered the major damaging factors responsible for a wide range of neurodegenerative disorders including both Parkinson's and Alzheimer's disease.
In the brain, epigallocatechin-3-gallate (EGCG) has been shown to act as an iron chelator, binding to and removing iron, thus preventing it from contributing to the production of free radicals. In addition to removing iron, EGCG also increases the activity of two major antioxidant enzymes, superoxide dismutase (SOD) and catalase, further helping to decrease free radical damage.
Another active compound in green tea, epicatechin (EC), reduces the formation of a protein called amyloid-beta. Plaque-like deposits of amyloid-beta in the brain are a defining characteristic of Alzheimer's disease.
Green tea polyphenols have also demonstrated the ability to affect cell signaling pathways, in particular the MAPK pathways, which are triggered by oxidative stress (free radicals), and themselves set in motion a series of chemical reactions so damaging that they can result in brain cell death. MAPK signaling pathways inside brain cells are thought to play a critical role in neurodegenerative diseases. Another important cell signaling pathway beneficially affected by EGCG, the PKC pathway, is also thought to play an essential role in the regulation of cell survival and programmed cell death.
Although no human studies on Alzheimer's disease have yet reported benefit from tea consumption, recent population studies have shown that simply consuming 2 or more cups of green tea daily reduces risk of cognitive decline and Parkinson's disease.
Green Tea Keeps Elders Mentally Sharp: Research Showing Multiple Ways
Green tea helps slow the age-related decline in brain function seen as declining memory, cognitive impairment, dementia and Alzheimer's, shows a human study published in the February 2006 issue of the American Journal of Clinical Nutrition.
Researchers at Japan's Tohoku University studied 1003 subjects over age 70, comparing their green tea intake and mental sharpness, using a Mini-Mental State Examination, a well-accepted standardized test for measuring cognitive function.
Drinking more than 2 cups a day of green tea slashed odds of cognitive impairment in elderly Japanese men and women by 64%! And a Japanese cup of green tea is much smaller than its American counterpart—only about 3.2 fluid ounces.
And at every level of cognitive impairment—from minimal to severe—those drinking the most green tea experienced significantly less mental decline than those drinking the least:
Compared with elderly Japanese who drank less than 3 cups a week, those drinking more than 2 cups a day had a 54% lower risk of age-related declines in memory, orientation, ability to follow commands and attention.
Those drinking 4 to 6 cups of green tea a week (1 cup a day) had a 38 lower risk of declines in brain function.
Green tea's primary protective agent is thought to be its catechin phytonutrient epigallocatechingallate or EGCG. Research shows this highly potent antioxidant:
helps prevent the formation of B-amyloid, a protein whose accumulation is recognized as causing Alzheimer's (Basianetto S, Eur J Neurosci Jan 2006).
protects brain cells by chelating (removing) iron, which might otherwise produce destructive free radicals (Reznichenko L, J Neurochem, March 2006).
helps prevent oxidative stress-induced brain cell death by "talking" to brain cells' genes responsible for cell cycling and survival. Specifically, EGCG tells the genes in neurons to decrease production of caspase 3, an enzyme involved in initiating programmed cell death. (Park HJ, Life Sci Jan 2006; Levites Y. J Biol Chem, 2002)
promotes memory-related learning ability by protecting cells in the hippocampus, a part of the brain involved in spatial cognition and memory-related learning ability, from free radical damage (Haque AM, J Nutr April 2006).
Green Tea Fights the Flu
A cup of green tea may help prevent or lessen the duration of the flu. In a lab study, published in the November 2005 issue of Antiviral Research, EGCG dramatically inhibited influenza virus replication in cell culture in all the subtypes of influenza virus tested. EGCG appears to suppress viral RNA synthesis by altering the properties of the viral membrane.
Pepper increases EGCG availability
An animal study suggests that consuming the spice, black pepper, when drinking green tea can significantly increase the amount of epigallocatechin-3-gallate (EGCG) absorbed. In this study, rats and mice given green tea along with piperine (a bioactive component in black pepper) absorbed 130% more EGCG than control animals receiving EGCG alone.
In this study, piperine was found to inhibit the glucuronidation of EGCG in the intestines. Glucuronidation is a chemical pathway that serves as one of the major ways our bodies convert drugs, steroids, and many other substances into metabolites that can then be excreted into the urine or bile. By inhibiting EGCG's glucuronidation, piperine allowed more of this catechin to be absorbed and utilized. So, next time you have a cup of green tea along with a meal, be sure to spice up your soup, salad and/or entrée with a little freshly ground black pepper.
Description
An oriental evergreen tree that can reach a height of 30 feet in the wild, the tea plant is kept as a shrub on tea plantations, where it is pruned to a height of about 3 feet to encourage new growth. A relative of the camellia with the botanical name of Camellia sinesis, the tea plant produces abundant foliage, a camellialike flower and berries containing one to two seeds. Only the smallest, youngest parts of the plant&mdah;the two leaves and bud at the tip of each new shoot—are picked for tea.
History
The tea plant, source of the most popular beverage in the world, is believed to have originated in the landmass encompassing Tibet, western China, and northern India. According to ancient Chinese legend, tea was discovered by the Chinese emperor Shen-Nung in 2737 B.C., when leaves from a wild tea bush accidentally fell into a pot of water he was boiling. The first recorded mention of tea appears in a contract for slaves known as "Tan Yuch," written by Wang Pao, poet laureate to Emperor Husan, in 59 B.C. By 780 A.D., when Lu Yu's The Classic of Tea was published in China, the cultivation and consumption of tea, whose name derives from the Chinese Amoy dialect word "t'e," pronounced "tay," had developed into a fine art. Today, "cha" means tea in Chinese. As this word moved westward into Middle Eastern languages, it sometimes became altered to “chai.”
India attributes the discovery of tea to the Buddhist monk Siddhartha in the 6th century. Legend has it that the prince-turned-monk traveled north from India to China to preach Buddhism, vowing he would meditate without sleeping for nine years. Reaching Canton in 519 A.D., he stationed himself before a wall of meditation where, after a mere five years, he was overcome by drowsiness. Inspired by divine intervention, he picked and chewed the leaves of a nearby tree, discovering, to his delight, a great sense of alertness and well-being. The tree whose health-giving properties enabled him to keep his vow was, of course, Camellia sinesis, whose leaves and seeds he carried with him as he continued his journey into Japan. In Japan, Buddhist monks quickly embraced tea, using it to remain alert during their own meditations and creating a simple drinking ritual that several hundred years later, tea master Sen-no Rikyu (1521-1591) developed into the high art of chanoyu, the Japanese tea ceremony.
From Japan, where tea was widely cultivated and consumed by the 9th century A.D., tea culture spread to Java, the Dutch East Indies, and other tropical and subtropical areas. In the 16th century, traders from Europe sailing to and from the Far East introduced Europeans to the delicious Asian drink, and by the 18th century, tea had become the national beverage of England.
Thousands of Chinese bushes stealthily acquired by botanist Robert Fortune, a "spy" for Great Britain's East India Trading Company, were introduced into India in the 1840s, where they quickly became a popular and profitable crop for the Empire.
Tea crossed the Atlantic with the American colonists, among whom its popularity led to the British imposition in 1767 of a tea tax that so infuriated the colonists that they revolted, tossing tons of tea into the harbor in 1733 in what became known as the Boston Tea Party. Freedom from unfair British taxation, symbolized by the tax on tea, became a central contributing factor to the Revolutionary War. The type of tea tossed into Boston harbor? Probably green since it was likely "gunpowder tea," green tea rolled tightly into pellets that looked like gunpowder shot to preserve its freshness during long voyages.
Several new innovations in tea consumption originated in the United States. In 1904, when a New York City merchant, Thomas Sullivan, sent his customers samples of tea in small silk bags, they found the bags could be used to conveniently brew a single cup of tea, and the tea bag was born. Another American innovation in tea drinking, instant tea, was first marketed in 1948.
Today, not China but India ranks as the number one producer of tea, although Sri Lanka (formerly Ceylon) is the major tea supplier to the U.S. Worldwide, more than 2.5 million metric tons of tea are produced each year with India, China, Sri Lanka, Kenya, Indonesia, Turkey, U.S.S.R, Japan, Iran and Bangladesh being the leading tea growing countries.
How to Select and Store
Whenever possible, ask for a sample of prepared tea before buying. Most high-quality teas will produce a pale green to yellow-green cup.
Loose Tea
To test for freshness, tightly squeeze a small amount and smell the aroma. The freshest, most flavorful tea will smell sweet and grassy.
Tea Bags
To test tea bags for freshness, remove the tea from one bag, place the empty bag in a cup, pour hot water over it., and let it steep for 2-3 minutes. If the result takes like plain hot water, the tea itself is likely fresh. If the tea bag water tastes like tea, the tea is old, and the paper has absorbed its flavor.
Since a single ounce of tea should produce 15 to 30 cups, the best way to ensure your tea is fresh is to purchase it in small amounts—two to four ounces at most. To retain freshness and flavor in both loose and bagged tea, store it in a tightly constructed opaque container to protect it from light, moisture and food odors.
Dark glass or ceramic containers are best; tins often leak as their seams are soldered. Use a small container just large enough to accommodate the amount of tea; tea exposed to the air in a half-empty large container will continue to oxidize.
It's best to store tea in a dark, cool, dry cupboard. Tea stored in the refrigerator is vulnerable to moisture and odors from other foods, and the water condensation that occurs when frozen tea is defrosted can ruin it.
The following are just a few delicious green teas available in most serious tea shops, mail-order catalogues and on-line sources of fine green teas:
Chinese Green Teas
The best Chinese green teas are thought to be those picked in early spring at the time of the Qing Ming festival, which takes place on April 5th of the solar calendar. These include:
After the Snow Sprouting: among the first tender sprouts available after the winter snows, these leaves produce a delicate tea with a fresh green scent.
Ching Ca: grown in mainland China, these teas include the famous Pi Lo Chun and Tai Ping Hou Gui.
Chun Mei (Precious Eyebrows): a name reflecting the fact that these springtime leaves are twisted into small curved shapes like lovely eyebrows. This high-grown tea from Yunnan province should be brewed lightly to produce an amber liquid with a wonderful aftertaste reminiscent of plums.
Dragonwell: with a fresh green taste, this is the favorite green tea of mainland China. The highest grade of this tea, Qing Ming, is named for the opening spring festival when the finest teas are picked.
Green Pearls: each pearl unfurls into three or four leaves that yield a lovely golden aromatic brew.
Gunpowder: a combination of buds and young green leaves rolled into balls reminiscent of gunpowder shot (hence its name), these also unfurl when infused. To test the freshness of gunpowder tea, pinch or squeeze a pellet. If fresh, it will resist; if stale, it will crumble. Two excellent gunpowder teas with a sweet, grassy taste are Gunpowder Pinhead Temple of Heaven and Gunpowder Temple of Heaven.
Guzhang Maohan (Mao Jin): these tea leaves from the Yellow Mountains of Anhui province produce a darker brew with a sweet, smoky flavor.
Pan Long Yin Hao: from Zhejiang province, this tea, a repeat winner in tea competitions conducted by the Chinese Ministry of Agriculture, is described as "a complex brew of multiple flavor notes."
Po Lo Chun: which translates to "Astounding Fragrance," aptly describes this slightly sweet yellowish tea with a lovely aftertaste.
Snow Dragon: grown near the border between Fujian and Zhejiang province, this tea is roasted in a large wok to produce a nutty, sweet flavor. Yunnan Green Needle: a pleasantly astringent clean-tasting tea made from delicate green buds.
Organic Green Teas
The most stringent standards for organic produce are found in California, Japan and Germany. Any tea that meets these standards is a high quality organic product.
The two most respected organic tea farms are in India: the Oothu Tea Estate, the first organic tea farm in the world, and Makaibari Tea Estates, which follows Rudolph Steiner's principles of harmony with nature through organic, sustainable methods of agriculture.
Indian Green Teas
Although green teas are a very small part of overall tea production in India, the following are notable.
Bherjan Estate: an organic green tea grown in Assam, India's most plentiful tea district. Assam teas are renowned for their hearty taste and "strength" in aroma and body.
Ambootia Tea Estate: a Darjeeling district organic green tea that produces a light, fragrant cup.
Makaibari Tea Estates: a multiple award winning Darjeeling green tea, flavorful but light.
Craigmore Estate: grown at high altitutes in the spectacular range of the Nilgiris, India's Blue Mountains, these green teas are exceptionally fragrant and sweet.
Japanese Green Teas
The best quality green teas are grown in the prefectures of Shizuoka and Uji.
Ban-cha: an earthy brown tea with an astringent taste made from roasted green tea leaves, bancha should only steep two to three minutes or it will become bitter.
Houjica: a lightly roasted bancha tea with a nutty flavor. A good nighttime choice as it is very light and low in caffeine.
Sen-cha: about 75% of the green tea harvested in Japan is Sencha, making it the most commonly consumed green tea in Japan. Sencha is especially rich in vitamin C and provides a clear rich yellow-green liquor that is grassy sweet and cleanly astringent. Made from a higher quality leaf than bancha or houjica, sencha is often called "guest tea." The most delightful sencha is Sencha Sakuro, a spring green tea scented with cherry blossoms. Another cherry-scented sencha to try is Spiderleg Sakuro whose longer, more "spidery" leaves produce a rich flavorful bouquet.
Gyokuro: the highest quality Japanese green tea, gyokuro has been called "history, philosophy and art in a single cup." For three weeks before the spring harvest, gyokuro leaves are shaded from direct sunlight, leading to a slower maturation that enhances the leaves' content of flavenols, amino acids, sugars and other substances that provide green tea's health benefits, aroma and taste. Intensely green and sweeter than sencha, gyokuro leaves can serve as the base for matcha—the silky chartreuse tea powder used to make chanoyu, the tea of the Japanese tea ceremony.
Mat-cha: Matcha differs from gyokuro in that the leaves are not rolled. After steaming, they are immediately and thoroughly dried, after which they are called tencha. Tencha is then ground into the superfine powder known as matcha. Use about two level teaspoons of matcha to ½ cup water and whip into a thick, invigorating brew, wonderful as an energizing morning tea or before exercise.
Shin-cha: In Japanese, "shin" means new and "cha" means tea. Shincha is literally "new tea" as it consists of leaves very lightly steamed immediately after harvesting. Shincha, which is only sold from May through July, is a highly aromatic tea with the aroma of freshly picked leaves. Because it is quite perishable, only a very small percentage of the tea harvest is processed as shincha; most of the leaves are used for sencha.
Genmai cha: Made from sencha mixed with genmai (puffed brown rice), this tea may be made from lower quality second harvest sencha but can also be found made from premium first-leaf sencha. The rice supplies a slightly nutty taste. Some tea retailers also add a pinch of matcha to the blend, giving it a vibrant green color.
How to Enjoy
Tips for Preparing
Green tea should be handled tenderly, just as you would fresh green leafy vegetables.
Spring water is the ideal choice for brewing tea, followed by filtered water. Distilled water should never be used; the brew it produces will be flat since the minerals removed from it are essential to bringing out tea's flavor.
To prepare the best loose tea, we recommend using a small food scale. Use three grams of tea to five ounces of water if brewing tea in a small teapot; four grams of tea to eight ounces of water for other methods.
As the size and shape of tea pots and cups varies considerably, it's a good idea to fill a measuring cup with 8 ounces of water and pour it into your tea pot or cup to determine how much water it really holds.
In making loose tea, remember that a teaspoon of small, dense leaves will weigh substantially more than a teaspoon of larger leaves, and the resulting tea will reflect this. A teaspoon of small dense leaves may be sufficient to produce a satisfying strong cup, while several teaspoons of larger leaves would be needed for a comparable brew.
Although heartily boiling water is used to brew black and oolong teas, green tea needs much lower temperatures (160-170 degrees F; 79-85 degrees C) and should be brewed for less time.
Let the water barely reach the boiling point to liberate its oxygen, then allow it to cool slightly before pouring over your tea. Until you are familiar with your tea kettle and the time it takes and sounds it makes when the correct temperature (170-185 degrees) has been reached, it's a good idea to check using a simple, inexpensive candy thermometer, available at any grocery store.
Brewing for 30 seconds to one minute is usually ideal; however, Nilgiri and Darjeeling greens can take several minutes, and Chinese Dragonwell teas are often best after 6-7 minutes of infusion.
Although good quality tea leaves will sink to the bottom after they have infused, it's a good idea to pour the tea over a small strainer if one is not built in to your teapot.
Quick Serving Ideas
Brew green tea with thinly sliced ginger and lemon, or sprigs of spearmint. Add one teaspoon of honey per cup, stir and serve hot or use half the amount of hot water (or twice the amount of tea), allow the tea to brew and cool, then pour over ice cubes.
Make a green tea chai by brewing green tea in hot vanilla soy milk and topping with a dash each of cinnamon, black pepper, ginger and allspice.
Brew 1-2 teaspoons loose leaf green tea in 8 ounces cool water for 20-30 minutes to develop flavor without bitterness and add to stir-fries, marinades, dressings, soups and sauces.
Sprinkle gyokuro tea over a salad, stew or rice dish.
Add ½ teaspoon gyokuro tea to an almost set omelet or scrambled eggs.
Add crushed gunpowder tea and rice vinegar to sesame oil for a delicious vinaigrette.
Mix gyokuro tea with sesame seeds and sea salt and use to dredge shrimp or fish filets before lightly pan-frying them.
Cook Japanese udon noodles in green tea for about 5 minutes, then remove from heat and leave noodles in tea until cool. Drain and toss lightly with soy sauce and sesame oil. Add thinly sliced tofu, scallions, mushrooms, and chopped cilantro, and serve.
Poach Asian or Bosc pears in green tea with fresh thinly sliced gingerroot. Drizzle with honey and top with a sprig of fresh mint.
Combine cooled green tea half and half with a fruit juice, such as peach, pineapple or papaya. Sweeten with a teaspoon of honey per cup. Blend and pour over ice.
Safety
Green Tea and Caffeine
Green tea contains caffeine, although half that found in coffee. The amount of caffeine that ends up in your cup of green tea will vary according to the amount of tea used, the length of time the leaves are infused, and if you drink the first or second infusion. Most of the caffeine in green tea is extracted into the water the first time the tea is infused.The table below compares the average amount of caffeine found in tea, other caffeinated drinks and chocolate.
There is limited research in the published literature comparing the caffeine content of green vs black tea. A recent study1 measured the caffeine content in the dry matter of the tea leaves, an approach that allows for control of any confounding variables related to preparation techniques that may impact the caffeine content in the final tea product. This study found that the caffeine content of one gram of black tea ranged from 22-28 milligrams while the caffeine content of one gram of green tea ranged from 11-20 milligrams, reflecting a significant difference. (Please note that not all of the caffeine from the tea leaves is extracted into the tea beverage, so these numbers only provide a relative level of caffeine difference between black and green tea, and not a reflection on the absolute amount contained in each tea beverage.)
Caffeine-containing Product Type of Product Caffeine (mg/serving)
Tea Green, black, oolong 50mg/190ml serving2
Green (different varieties) 20-45mg/8oz serving3
Black 47mg/8oz serving4
Coffee Brewed (filter or percolated) 100-115mg/190ml serving2
Instant 75mg/190ml serving2
Cola drinks Standard and Sugar Free 11-70mg/330ml can5
'Energy drinks' All types 28-87mg/250ml serving5
Chocolate Bar 5.5-35.5mg/50g bar5
1. Khokhar S, Magnusdottir SG. Total phenol, catechin, and caffeine contents of teas commonly consumed in the United kingdom. J Agric Food Chem. 2002 Jan 30;50(3):565-70.
2.Gray J (1998). Caffeine, coffee and health. Nutrition and Food Science 6:314-319.
3. Unpublished data
4. USDA National Nutrient Database for Standard Reference, Release 17 (2004)
5. Ministry of Agriculture, Fisheries and Food (MAFF) (1998). Survey of caffeine and other methylxanthines in energy drinks and other caffeine containing products (updated). Food Surveillance Information Sheet No. 144 (No. 103 revised). London.
Source: Tea Council Fact Sheet, http://www.teacouncil.co.uk/
What is a safe intake of caffeine?
The safety of caffeine consumption remains a topic of major debate in the research literature. To our knowledge, no studies have shown problems with caffeine consumption of less than 75 milligrams per day. Most studies showing potentially problematic effects of caffeine consumption have focused on intakes above 200 milligrams. In addition, there appears to be a significant difference in people’s sensitivity to caffeine. People sensitive to caffeine may wish to drink a decaffeinated green tea or, since approximately 80% of the caffeine is released in the first infusion, simply infuse the tea for 45 seconds in hot water, then pour off the liquid. Add more hot water and steep again. This method removes most of the tea's caffeine but little of its flavor and aroma.
At least two beneficial components in green tea—its catechins and the amino acid L-theanine—lessen the impact of its caffeine. When green tea is brewed, its caffeine combines with catechins in the water, reducing the caffeine's activity compared to coffee or cocoa. In addition, L-theanine, which is only found in tea plants and some mushrooms, directly stimulates the production of alpha brain waves, calming the body while promoting a state of relaxed awareness.
Green Tea and Drug Interactions
The tannins in green tea may decrease the absorption and thus the activity of the following drugs: atropine, Cardec DM®, codeine, ephedrine and pseudoephedrine, Lomotil®, Lonox®, theoplylline, aminophylline, and warfarin.
The caffeine in green tea may interact with the following drugs heightening their effects to dangerous levels: ephedrine and pseudoephedrine, theophylline, aminophylline.
Green Tea and Iron Absorption
Due to their high tannin-content, teas, including green tea, have been shown to prevent iron absorption. While this effect is helpful in persons with too much iron, consuming several cups of green tea daily may not be a good idea for persons deficient in iron or susceptible to iron deficiency.
Limit Green Tea Consumption During the First Trimester of Pregnancy
According to a study published in the March 2005 issue of Cancer Research, ECGC, a catechin present in green tea in amounts about 5 times higher than in black tea, inhibits the enzyme dihydrofolate reductase (DHFR), which cancer cells need to be able to grow, and which is a well recognized target of anti-cancer drugs.
Scientists decided to look at ECGC after they realized the green tea catechin looks a lot like the cancer drug methotrexate, which prevents cancer cells from making DNA by inhibiting the DHFR enzyme. They discovered that ECGC kills cancer cells in the same way as the drug.
Although ECGC binds strongly to DHFR, which is essential in both healthy and cancerous cells, it does not bind as tightly as methotrexate, so its side effects on healthy cells are less severe than those of the drug.
ECGC's binding to DHFR may also explain why women who drink large amounts of green tea around the time they conceive and early in their pregnancy may have an increased risk of having a child with spina bifida or other neural tube disorders.
Women are advised to take supplements of folic acid when trying to conceive and during the first trimester (the first 3 months) of pregnancy because it is during this time period that the baby's neural tube is developing. Folic acid helps ensure normal development and protects against spina bifida by enabling the production of the enzyme DHFR. While a cup or two of green tea is unlikely to pose a problem, drinking large amounts of green tea could decrease the activity of DHFR, increasing risk of neural tube defects.
Nutritional Profile
Introduction to Food Rating System Chart
The following chart shows the nutrients for which this food is either an excellent, very good or good source. Next to the nutrient name you will find the following information: the amount of the nutrient that is included in the noted serving of this food; the %Daily Value (DV) that that amount represents (similar to other information presented in the website, this DV is calculated for 25-50 year old healthy woman); the nutrient density rating; and, the food's World's Healthiest Foods Rating. Underneath the chart is a table that summarizes how the ratings were devised. For more detailed information on our Food and Recipe Rating System, please click here.
Green tea
0.07 ounces
0.00 calories
Nutrient Amount DV
(%) Nutrient
Density World's Healthiest
Foods Rating
World's Healthiest
Foods Rating Rule
excellent DV>=75% OR Density>=7.6 AND DV>=10%
very good DV>=50% OR Density>=3.4 AND DV>=5%
good DV>=25% OR Density>=1.5 AND DV>=2.5%
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This page was updated on: 2006-05-07 15:00:18
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