Green tea (Camellia sinensis)
  
Green tea (Camellia sinensis)
Background
Green tea is made from the dried leaves of Camellia sinensis , a perennial evergreen shrub. Green tea has a long history of use, dating back to China approximately 5000 years ago. Green tea, black tea, and oolong tea are all derived from the same plant.
Green tea is a source of caffeine, a methylxanthine which stimulates the central nervous system, relaxes smooth muscle in the airways to the lungs (bronchioles), stimulates the heart, and acts on the kidney as a diuretic (increasing urine). One cup of tea contains approximately 50 milligrams of caffeine, depending on the strength and size of cup (as compared to coffee which contains 65 to 175 milligrams of caffeine per cup). Tea also contains polyphenols (catechins, anthocyanins, phenolic acids), tannin, trace elements, and vitamins.
The tea plant is native to Southeast Asia that can grow up to a height of 40 feet, but is usually maintained at a height of two to three feet by regular pruning. The first spring leaf buds, called the first flush , are considered the highest-quality leaves. When the first flush leaf bud is picked, another one grows, which is called the second flush , and this continues until an autumn flush . The older leaves picked farther down the stems are considered to be of poorer quality.
Tea varieties reflect the growing region (for example, Ceylon or Assam), the district (for example, Darjeeling), the form (for example, pekoe is cut, gunpowder is rolled), and the processing method (for example, black, green, or oolong). India and Sri Lanka are the major producers of Green tea.
Green tea is produced by lightly steaming the freshly cut leaf, thus not allowing oxidation of the enzymes within the leaf to take place. Green tea is produced and consumed primarily in China, Japan, and countries in North Africa and the Middle East. In contrast, allowing the leaves of Camellia sinesis to oxidize produces black tea (a fermentation process which alters flavor as well as enzymes present in the tea). Oolong tea is a partially oxidized tea and accounts for less than 5% of all the tea produced.
Historically, tea has been served as a part of various ceremonies, and has been used to stay alert during long meditations. A legend in India describes the story of Prince Siddhartha Gautama, the founder of Buddhism, who tore off his eyelids in frustration at his inability to stay awake during meditation while journeying through China. A tea plant is said to have sprouted from the spot where his eyelids fell, providing him with the ability to stay awake, meditate, and reach enlightenment. Turkish traders reportedly introduced tea to Western cultures in the 6th century.
Synonyms
AR25®, Camellia, Camellia assamica , Camellia sinensis , Camellia sinensis (L.) Kuntze, Camellia tea, Catechins, Chinese Tea, EGCG, Epigallocatechin-3-gallate, Exolise®, GTE, Green Tea Extract, Matsu-cha Tea, Thea sinensis , Thea bohea , Thea viridis , Theanine, Theifers.
Evidence
These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Uses based on scientific evidenceGrade*Cancer prevention
Several large population-based studies have been undertaken to examine the possible association between green tea consumption and cancer incidence. Cancers of the digestive system (stomach, colon, rectum, pancreas, and esophagus) have primarily been tracked. The risk of prostate cancer, cervical cancer and breast cancer in women has also been studied. Although much of this research suggests cancer-protective properties of habitual green tea consumption, some studies have not observed significant benefits. In studies that have shown benefits, it is not clear if other lifestyle choices of people who drink tea may actually be the beneficial factors. If there is a benefit, it may be small and require large amounts of daily consumption (several cups per day). At this time, the scientific evidence remains indeterminate in this area. Laboratory and animal studies report that components of tea, such as polyphenols, have antioxidant/free radical scavenging properties and may possess various effects against tumor cells (such as angiogenesis inhibition, hydrogen peroxide generation or induction of apoptosis). Limited human study reports lower estrogen levels in women drinking green tea, proposed as possibly beneficial in estrogen-receptor positive breast cancers. However, other animal and laboratory research suggests that components of green tea may actually be carcinogenic, although effects in humans are not clear. Overall, the relationship of green tea consumption and human cancer remains unclear. Evidence from a controlled trial of sufficient size and duration is needed before a recommendation can be made in this area.
C
Heart attack prevention
There is early suggestive evidence that regular intake of green tea may reduce the risk of heart attack or atherosclerosis (clogged arteries). Tea may cause a decrease in platelet aggregation or endothelial dysfunction, proposed to be beneficial against blockage of arteries in the heart. Evidence from controlled trials of sufficient size and duration are needed before a recommendation can be made in this area.
C
High cholesterol
Laboratory, animal studies and limited human research suggest possible effects of green tea on cholesterol levels. Recent research using a theaflavin-enriched green tea extract is promising. Better human evidence is necessary in this area.
C
Mental performance/alertness
Limited, low-quality research reports that the use of green tea may improve cognition and sense of alertness. Green tea contains caffeine, which is a stimulant.
C
Memory enhancement
Several preliminary studies have examined the effects of caffeine, tea, or coffee use on short and long-term memory. It remains unclear if tea is beneficial for this use.
C
Dental cavity prevention
There is limited study of tea as a gargle (mouthwash) for the prevention of dental cavities (caries). It is not clear if this is a beneficial therapy.
C
Sun protection
There is limited animal and human study of green tea as a protective agent of skin from ultraviolet light skin injury. Well-designed research is needed before a recommendation can be made in this area. Comparisons have not been made with well-established forms of sun protection such as ultraviolet protective sunscreen.
C
Asthma
Research has shown caffeine to cause improvements in airflow to the lungs (bronchodilation). However, it is not clear if caffeine or tea use has significant clinical benefits in people with asthma. Better research is needed in this area before a conclusion can be drawn.
C
Weight loss
There are several small human studies addressing the use of green tea extract (GTE) capsules for weight loss in overweight or average weight individuals. Better research is needed before a recommendation can be made in this area.
C
Arthritis
Research indicates that green tea may benefit arthritis by reducing inflammation and slowing cartilage breakdown. Further studies are required before a recommendation can be made.
C
Menopausal Symptoms
A study conducted in healthy postmenopausal women showed that a morning/evening menopausal formula containing green tea was effective in relieving menopausal symptoms including hot flashes and sleep disturbance. Further studies are needed to confirm these results.
C
* Key to grades
A: Strong scientific evidence for this use;
B: Good scientific evidence for this use;
C: Unclear scientific evidence for this use;
D: Fair scientific evidence against this use (it may not work);
F: Strong scientific evidence against this use (it likely does not work).
Uses based on tradition or theory
The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Alcohol intoxication, antioxidant, astringent, bone density improvement, cataracts, cognitive performance enhancement, Crohn's disease, detoxification from alcohol or toxins, diabetes, diarrhea, diuretic (increasing urine), fibrosarcoma, flatulence, fungal infections, gastritis, gum swelling, headache, heart disease, infection, HIV/AIDS, improving blood flow, improving urine flow, improving resistance to disease, inhibition of platelet aggregation, ischemia-reperfusion injury protection, joint pain, kidney stone prevention, liver cancer, longevity, lung cancer, neuroprotection, oral leukoplakia, ovarian cancer, Parkinson's disease prevention, promotion of digestion, protection against asbestos lung injury, regulation of body temperature, stimulant, stomach disorders, bleeding of gums or tooth sockets, stroke prevention, sunburn, tired eyes, vomiting.
Dosing
The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.
Adult oral dosing (18 years and older):
Benefits of specific doses of green tea are not established. Most studies have examined green tea in the form of a brewed beverage, rather than in capsule form. One cup of tea contains approximately 50 milligrams of caffeine and 80 to 100 milligrams of polyphenol content, depending on the strength and size of cup. For cancer prevention, studies have examined the effects of habitually drinking anywhere from 1 to 10 cups per day (or greater). For heart disease prevention, one study reports benefits of drinking greater than 375 milliliters of tea per day, although evidence in this area remains unclear.
In capsule form, there is considerable variation in the amount of green tea extract (GTE) per capsule, anywhere from 100 to 750 milligrams per capsule. Extracts of green tea may be standardized to contain anywhere from 60 to 97 percent polyphenols. A 2001 phase I study by Pisters et al. reported that the maximum-tolerated dose of oral green tea extract (GTE) is 4.2 grams per meter squared daily taken daily once or in three divided doses (equivalent to 7 or 8 Japanese cups), or 120 milliliters of green tea three times daily. Currently, there is no established recommended dose for GTE capsules.
Safety
The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.
Allergies
People with known allergy/hypersensitivity to caffeine or tannin should avoid green tea. Skin rash and hives have been reported with caffeine ingestion.
Side Effects and Warnings
Studies of the side effects of green tea specifically are limited. However, green tea is a source of caffeine, for which multiple reactions are reported.
Caffeine is a stimulant of the central nervous system, and may cause insomnia in adults, children, and infants (including nursing infants of mothers taking caffeine). Caffeine acts on the kidneys as a diuretic (increasing urine and urine sodium/potassium levels, and potentially decreasing blood sodium/potassium levels), and may worsen urge incontinence. Caffeine-containing beverages may increase the production of stomach acid, and may worsen ulcer symptoms. Tannin in tea can cause constipation. Caffeine in doses of 250 to 350 milligrams can increase heart rate and blood pressure, although people who consume caffeine regularly do not seem to experience these effects in the long-term.
An increase in blood sugar levels may occur after drinking green tea containing the equivalent of 200 milligrams of caffeine (4 to 5 cups, depending on tea strength and cup size). Caffeine-containing beverages such as green tea should be used cautiously in patients with diabetes. In contrast, lowering of blood sugar levels from drinking green tea has also been reported in preliminary research. Additional study is needed in this area.
People with severe liver disease should use caffeine cautiously, as levels of caffeine in the blood may build up and last longer. Skin rashes have been associated with caffeine ingestion. In laboratory and animal studies, caffeine has been found to affect blood clotting, although effects in humans are not known.
Caffeine toxicity/high doses : When the equivalent or more than 500 milligrams of caffeine are consumed (usually more than 8 to 10 cups per day, depending on strength and size of cups), symptoms of anxiety, delirium, agitation, psychosis, or detrussor instability (unstable bladder) may occur. Conception may be delayed in women who consume large amounts of caffeine. Seizure, muscle spasm, life-threatening muscle breakdown (rhabdomyolysis), and life-threatening abnormal heart rhythms have been reported with caffeine overdose. Doses greater than 1000 milligrams may be fatal.
Caffeine withdrawal : Chronic use can result in tolerance, psychological dependence, and may be habit forming. Abrupt discontinuation may result in withdrawal symptoms such as headache, irritation, nervousness, anxiety, tremor, or dizziness. In people with psychiatric disorders such as affective disorder or schizoaffective disorder, caffeine withdrawal may worsen symptoms or cause confusion, disorientation, excitement, restlessness, violent behavior, or mania.
Chronic effects : Several population studies initially suggested a possible association between caffeine use and fibrocystic breast disease, although more recent research has not found this connection. Limited research reports a possible relationship between caffeine use and multiple sclerosis, although evidence is not definitive in this area. Animal study reports that tannin fractions from tea plants may increase the risk of cancer, although it is not clear that the tannin present in green tea has significant carcinogenic effects in humans.
Drinking tannin-containing beverages such as tea may contribute to iron deficiency, and in infants, tea has been associated with impaired iron metabolism and microcytic anemia.
In preliminary research, green tea has been associated with decreased levels of estrogens in the body. It is not clear if significant side effects such as hot flashes may occur.
Pregnancy and Breastfeeding
Large amounts of green tea should be used cautiously in pregnant women, as caffeine crosses the placenta and has been associated with spontaneous abortion, intrauterine growth retardation, and low birth weight. Heavy caffeine intake (400 milligrams per day or greater) during pregnancy may increase the risk of later developing SIDS (sudden infant death syndrome). Very high doses of caffeine (greater than or equal to 1100 milligrams daily) have been associated with birth defects, including limb and palate malformations.
Caffeine is readily transferred into breast milk. Caffeine ingestion by infants can lead to sleep disturbances/insomnia. Infants nursing from mothers consuming greater than 500 milligrams of caffeine daily have been reported to experience tremors and heart rhythm abnormalities. Components present in breast milk may reduce infants' ability to metabolize caffeine, resulting in higher than expected blood levels. Tea consumption by infants has been associated with anemia, reductions in iron metabolism, and irritability.
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