Green Tea Health Benefits

by MedlinePlus

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 sinensis 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®, FertilityBlend (containing chasteberry, green tea extracts, L-arginine, vitamins (including folate) and minerals), 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 evidence

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.

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.

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.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). Preliminary data shows that drinking 4 cups/day of decaffeinated green or black tea may decrease the amount of DNA damage in heavy smokers. 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.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.Overall, the relationship of green tea consumption and human cancer remains inconclusive. Evidence from a controlled trial of sufficient size and duration is needed before a recommendation can be made in this area.

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.

Fertility

Early research using a product called FertilityBlend (containing chasteberry, green tea extracts, L-arginine, vitamins (including folate) and minerals) 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.

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.

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.

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.

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.

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.

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.

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. 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.

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, astringent, autoimmune encephalomyelitis, bone density improvement, bladder cancer, cataracts, cognitive performance enhancement, Crohn's disease, detoxification from alcohol or toxins, dementia, diabetes, diarrhea, diuretic (increasing urine), fibrosarcoma, flatulence, fungal infections, gastritis, gingivitis, gum swelling, headache, heart disease,Helicobacter pyloriinfection, 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, lymphocytic leukemia, liver cancer, longevity, neuroprotection, oral leukoplakia, ovarian cancer, Parkinson's disease prevention, promotion of digestion, prostate cancer, protection against asbestos lung injury, regulation of body temperature, stimulant, stomach disorders, bleeding of gums or tooth sockets, stroke prevention, sunburn, tired eyes, vascular tumors, vomiting.

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