Green tea (Camellia sinensis)

 
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Green tea
Green tea

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 5,000 years ago. Green tea, black tea, and oolong tea are all derived from the same plant.

 

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.

 

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®, flavonol, GTE, Green Tea Extract, Matsu-cha Tea, polyphenols, Polyphenon E,  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 evidence Grade*
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
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 benefits in people with asthma. Better research is needed in this area before a conclusion can be drawn.

C
Cancer prevention

Overall, the relationship of green tea consumption and human cancer remains inconclusive. Evidence from well-designed clinical trials is needed before a firm recommendation can be made in this area.

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
Diabetes

More studies are required to determine if green tea, and polyphenols, have any therapeutic benefit for diabetes prevention or treatment.

C
Fertility

Early research using a combination product called FertilityBlend has been associated with some success in helping women to conceive. Further well-designed research on green tea alone for this use is needed before a conclusion can be drawn.

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). Further well-designed clinical trials are needed before a recommendation can be made in this area.

C
High cholesterol or triglycerides

Laboratory, animal studies and limited human research suggest possible effects of green tea on cholesterol and triglyceride levels. Better human evidence is necessary in this area.

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
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
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
Prostate cancer (treatment)

One clinical trial showed minimal benefit using green tea extract capsules for the treatment of hormone refractory prostate cancer. Further research is needed before a recommendation can be made.

C
Sun protection/ skin damage

There is limited animal and human study of green tea as a protective agent of skin from ultraviolet light skin injury. Some study results conflict. Comparisons have not been made with well-established forms of sun protection such as ultraviolet protective sunscreen. The effects of green tea on skin damage caused by the sun remain unclear.

C
Weight loss (maintenance)

There are several small human studies addressing the use of green tea extract (GTE) capsules for weight loss or weight maintenance in overweight or average weight individuals. Study results are mixed. Better research is needed before a recommendation can be made in this area.

C
Anxiety

L-theanine is a predominant amino acid found in green tea. Preliminary research exists on the effects of this amino acid in comparison with the prescription drug alprazolam on experimentally induced anxiety. No benefit was found.

D

 

*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;
F: Strong scientific evidence against this use.

 

Grading rationale

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.

Adenocarcinoma, alcohol intoxication, antioxidant, artherosclerosis, astringent, autoimmune encephalomyelitis, bladder cancer, bleeding of gums or tooth sockets, bone density improvement, cataracts, cognitive performance enhancement, coronary heart disease, Crohn's disease, dementia, detoxification from alcohol or toxins, diarrhea, digestion, diuretic (increasing urine), exercise performance, fibrosarcoma, flatulence, fungal infections, gastritis, gingivitis, gum swelling, headache, heart disease,Helicobacter pyloriinfection, HIV/AIDS, improving blood flow, improving resistance to disease, , improving urine flow, inhibition of platelet aggregation, ischemia-reperfusion injury protection, joint pain, kidney stone prevention, liver cancer, longevity, lung cancer, lymphocytic leukemia, neuroprotection, oral leukoplakia, ovarian cancer, Parkinson's disease (prevention), protection against asbestos lung injury, regulation of body temperature, stimulant, stomach disorders, stroke prevention, tired eyes, vascular tumors, 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 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.

 

Studies have examined the effects of habitually drinking anywhere from 1 to 10 cups per day (or greater).

 

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. 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. Certain doses of caffeine 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. 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 is possible with high doses. Chronic use can result in tolerance, psychological dependence, and may be habit forming. Abrupt discontinuation may result in withdrawal symptoms.

 

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.

 

Caffeine is readily transferred into breast milk. Caffeine ingestion by infants can lead to sleep disturbances/insomnia.

 

Interactions

Most herbs and supplements have not been thoroughly tested for interactions with other herbs, supplements, drugs, or foods. The interactions listed below are based on reports in scientific publications, laboratory experiments, or traditional use. 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.

Interactions with Drugs
Studies of the interactions of green tea with drugs are limited. However, green tea is a source of caffeine, for which multiple interactions have been documented.

 

The combination of caffeine with ephedrine, an ephedra alkaloid, has been implicated in numerous severe or life-threatening cardiovascular events such as very high blood pressure, stroke, or heart attack. Stroke has also been reported after the nasal ingestion of caffeine with amphetamine.

 

Caffeine may add to the effects and side effects of other stimulants including nicotine, beta-agonists such as albuterol (Ventolin®), or other methylxanthines such as theophylline. Conversely, caffeine can counteract drowsy effects and mental slowness caused by benzodiazepines like lorazepam (Ativan®) or diazepam (Valium®). Phenylpropanolamine and caffeine should not be used together due to reports of numerous potentially serious adverse effects, although forms of phenylpropanolamine taken by mouth have been removed from the U.S. market due to reports of bleeding into the head.

 

When taken with caffeine, a number of drugs may increase caffeine blood levels or the length of time caffeine acts on the body, including disulfiram (Antabuse®), oral contraceptives (OCPs) or hormone replacement therapy (HRT), ciprofloxacin (Cipro®), norfloxacin, fluvoxamine (Luvox®), cimetidine (Tagamet®), verapamil, and mexiletine. Caffeine levels may be lowered by taking dexamethasone (Decadron®). The metabolism of caffeine by the liver may be affected by multiple drugs, although the effects in humans are not clear.

 

Caffeine may lengthen the effects of carbamazepine or increase the effects of clozapine (Clozaril®) and dipyridamole. Caffeine may affect serum lithium levels, and abrupt cessation of caffeine use by regular caffeine users taking lithium may result in high levels of lithium or lithium toxicity. Levels of aspirin or phenobarbital may be lowered in the body, although clinical effects in humans are not clear.

 

Although caffeine by itself does not appear to have pain-relieving properties, it is used in combination with ergotamine tartrate in the treatment of migraine or cluster headaches (for example, Cafergot®). It has been shown to increase the headache relieving effects of other pain relievers such as acetaminophen and aspirin (for example, Excedrin®). Caffeine may also increase the pain relieving effects of codeine or ibuprofen (Advil®, Motrin®).

 

As a diuretic, caffeine increases urine and sodium losses through the kidney, and may add to the effects of other diuretics such as furosemide (Lasix®).

 

Green tea may contain vitamin K, which when used in large quantities can reduce the blood thinning effects of warfarin (Coumadin®), a phenomenon that has been reported in a human case.

 

Based on preliminary data, theanine, a specific glutamate derivative in green tea, may reduce the adverse reactions caused to the heart and liver by the prescription cancer drug doxorubicin. Further research is needed to confirm these results.

 

Based on preliminary data, ingestion of green tea may lower LDL cholesterol, and thus may theoretically interact with other cholesterol-lowering drugs.

 

Other potential interactions may include drugs such as adenosine, alcohol, antidiabetics, antipsychotics, fluconazole, hydrocortisone, levodopa, MAOI antidepressants, phenytoin, proton pump inhibitors (PPIs), riluzole and timolol.

 

Interactions with Herbs and Dietary Supplements
Studies of green tea interactions with herbs and supplements are limited. However, green tea is a source of caffeine, for which multiple interactions have been documented.

 

Caffeine may add to the effects and side effects of other stimulants. The combination of caffeine with ephedrine, which is present in ephedra (ma huang), has been implicated in numerous severe or life-threatening cardiovascular events such as very high blood pressure, stroke, or heart attack.

 

Cola nut, guarana ( Paullina cupana ), and yerba mate ( Ilex paraguariensis ) are also sources of caffeine, and may add to the effects and side effects of caffeine in green tea. A combination product containing caffeine, yerbe mate ( Ilex paraguariensis ), and damiana ( Turnera difussa ) has been reported to cause weight loss, slowing of the gastrointestinal tract, and a feeling of stomach fullness.

 

As a diuretic, caffeine increases urine and sodium losses through the kidney, and may add to the effects of other diuretic agents.

 

Based on preliminary data, ingestion of green tea may lower LDL cholesterol, and thus may theoretically interact with other cholesterol-lowering herbs and supplements.

 

Bitter orange, calcium, iron, MAOIs, and tannin-containing herbs and supplements may also interact with green tea.

 

Interactions with Food
The bioavailability of catechins, constituents of green tea, may decrease when ingested with food. Green tea may also interact with grapefruit juice or milk.