green tea

n.
Tea made from leaves that are not fermented before being dried.

Background

In 1992, global production of all tea was almost 2.5 million tons. The majority of tea production occurs in the subtropical areas of Asia, including China, India, Sri Lanka, Japan, and Indonesia. More than 35 countries now produce tea, with India, China, and Sri Lanka the leaders. Black tea is the most produced, followed by oolong and jasmine tea. Besides the distinction between varieties of tea, the major difference between the type of teas is the processing method. Green tea leaves are picked and immediately sent to be dried or steamed to prevent fermentation, whereas black tea and other types are left to ferment after they are picked.

Green tea originated in China for medicinal purposes, and its first recorded use was 4,000 years ago. By the third century, it became a daily drink and cultivation and processing began. Today, China has hundreds of different types of green teas. Other producers of green tea include India, Indonesia, Korea, Nepal, Sri Lanka, Taiwan, and Vietnam.

Green tea was first introduced in Japan during the Nara period (710-794), when numerous Japanese Buddhist monks visited China and brought tea seeds back to Japan. The Japanese tea industry is said to have begun in 1191, when the monk Eisai planted tea seeds from China on temple land. He then encouraged the cultivation of tea in other areas of Japan by extolling the health benefits of tea drinking.

The making and serving tea as an art form (sado, the way of tea) was introduced in Japan during the eleventh century. The origins go back to China's Tang dynasty (618-907), when a ritual was performed in Buddhist temples. A brick of tea was ground to a powder, mixed in a kettle with hot water, and ladled into ceramic bowls.

One of the first Japanese uses of the tea ceremony in public was when Toyotomi Hideyoshi, then the most powerful warlord in Japan, held a tea party in his camp the evening before a large battle in order to calm his warriors and inspire morale. Hideyoshi's own sado teacher, Senno Rikyo, is also credited with elevating tea from a simple beverage to a highly respected method of self-realization. Today, there are tea schools in Japan to learn the proper methods of the tea ceremony or chanoyu. The Urasenke School is the most active and has the largest following.

The form of chanoyu that is practiced today was established in the second half of the sixteenth century by Rikyu. Chanoyu involves more than merely enjoying a cup of tea in a stylized manner. The ceremony developed under the influence of Zen Buddhism aims to purify the soul by becoming one with nature. The true spirit of the tea ceremony has been described by such terms as calmness, rusticity, and gracefulness. The rules of etiquette are carefully calculated to achieve the highest possible economy of movement.

For some 500 years after tea was introduced to Japan, it was used in its powdered form only. It was not until the mid-sixteenth century that the processing method for conventional green tea was invented. Prior to the Edo period (1600-1868), the consumption of tea was limited to the ruling class. Only after the beginning of the twentieth century, with the introduction of mass production techniques, did tea achieve widespread popularity among the general population.

Today, tea leaves for green tea are grown in the warmer southern regions of Japan, with about half produced in Shizuoka Prefecture. Uji, a district near the ancient city of Kyoto (and the district from which the finest Japanese tea comes from to this day) became the first tea-growing region in Japan. Later, tea plantations were planted in Shizuoka Prefecture and, finally to surrounding regions. A total of about 100,000 tons of green tea is produced per year from 60,000 hectares of tea fields. Only green tea is produced in Japan.

Though traditionally green tea was produced manually, the process has been fully mechanized in Japan. The various types of tea now produced differ according to cultivation practices and processing methods. Sencha is a tea with three quality levels: high, medium, and low. It is manufactured from the tender top two leaves and the shoots for the high and medium grades and from the third from the top leaf for the low grade.

Sencha, which comprises 80% of all green tea production, consists of tiny dark green needle-shaped pieces. Almost immediately after picking, the leaves are steamed for about 30 seconds to seal in the flavor, followed by drying, pressing, and rolling steps.

Gyokura is the highest grade of tea and is made from the most tender leaves that are grown under 90% shade using bamboo blinds. Matcha is made from similar leaves and is processed into a powder form for exclusive use in the tea ceremony. Bancha is a low-grade coarse tea made from older leaves picked after Sencha leaves are picked or picked in the summer. It is generally composed of lower grade tea leaves, which are divided into two kinds: large leaf, and small leaf.

Houjicha is a wedge-shaped tea made from Bancha that is roasted at 302° F (150° C) to prevent fermentation and produces a light golden color when made. Kamairicha comes from northern Kyushu and is first roasted at 392-572°F (200-300°C) followed by cooling at 212°F (100°C). Green tea is traditionally served without sugar, milk, or lemon since these would destroy the true flavor and aroma of the tea.

Raw Materials

Green tea is made from the top two leaves and buds of a shrub, Camellia sinensis, of the family Theaceace and the order Theales. This order consists of 40 genera of trees or shrubs that have evergreen leaves, flowers with five sepal or leaf-like structures and petals. The genus Camellia consists of 80 species of East Asian evergreen shrubs and trees. Besides the leaves, other ingredients may be added to create special scents or flavors during the drying process, such as jasmine, flowers, or fruits.

The tea plant originates in an area between India and China. There are three main varieties of this plant—China, Assam, and Cambodia—and a number of hybrids in between. The China variety grows as high as 9 ft (2.7 m) and has an economic life of at least 100 years. The Assam variety is a tree that grows as high as 60 ft (18.3 m), with an economic life of 40 years dependent upon regular pruning and plucking. The 16 ft (4.9 m) high Cambodia variety is naturally crossed with other varieties.

The Manufacturing
Process

Cultivation and harvesting

• A suitable climate for cultivation has a minimum annual rainfall of 45-50 in (114.3-127 cm). Tea soils must be acid since tea plants will not grow in alkaline soils. A desirable pH value is 5.8-5.4 or less. Tea can be cultivated up to 7,218.2 ft (2,200 m) above sea level and can grow between the equator and the forty-fifth latitude. The plants are reproduced through tile-laying or through seeds from trees that have grown freely.
• A crop of 1,500 lb (681 kg) of tea per acre requires up to two workers per acre to pluck the tea shoots by hand and maintain the field. The tea plant is generally plucked every five to 10 days, depending on where it grows. The length of time needed for the plucked shoot to redevelop a new shoot ready for plucking varies according to the plucking system and the climatic conditions. Intervals of between 70-90 days are common.
• In Japan, the tea harvesting begins around the end of April, with the leaves picked by hand or machine. A bud and several leaves are picked from each plant. The first crop is harvested in April and May, the second crop in June, the third crop in July and the final crop in September. For gyokuro or matcha tea, the plants are shaded for two weeks after the first bud comes out in spring before picking. The leaves are then shipped to the factory for processing. Since not all can be processed at once, the leaves are stored in a large bin that is kept at the proper temperature by blowing cool air into the bottom.

Drying

• After the tea leaves are plucked, they must be dried to prevent fermentation, which stops any enzyme activity that causes oxidation. In China, green teas are often pan-fired in very large woks, over a flame or using an electric wok. The tea leaves must be stirred constantly for even drying. Withering is also used, which spreads the tea leaves on racks of bamboo or woven straw to dry in the sun or using warm air. Again, the leaves must be moved around to ensure uniform drying.
• In Japan, steaming is normally used. Before the steaming process begins, the tea leaves are sorted and cleaned. The steaming time determines the type of tea that is produced. Sencha tea is normally steamed for 30-90 seconds. Another type of sencha called fukamushi is steamed for 90-150 seconds to produce a flaky light yellowish green tea. Steaming is conducted in a bamboo tray over water or by a revolving or belt-conveyor type machine. After mechanical steaming, the leaves go into a cooling machine that blows the water from the leaves.

Shaping

• In most countries, rolling or shaping green tea leaves is done by machinery. In China, high-end leaves are hand-rolled into various shapes, including curly, twisted, pointed, round, and more. Rolling the tea creates a distinctive look, as well as regulates the release of natural substances and flavor when it is steeped in the cup.
• In Japan, a number of rolling and drying steps take place. A special machine is used to accomplish the first rolling and drying steps simultaneously and takes about 48 minutes. The tea leaves are dried to improve their strength so they can be pressed during the next drying process. Moisture from both the surface and from the inside of the tea leaves is removed using this machine.
• This machine consists of a spindle with finger-shaped extensions that stir the leaves while heated air (at 93.2-96.8° F [34-36° C]) is blown into the machine. Though the rolling temperature is automatically controlled by the computer, it is still important for the operator to touch the tea by hand to make sure it feels right.
• Since the moisture level still varies for different parts of a leaf or from one leaf to another at the end of the first step, another rolling process takes place to uniformly distribute the remaining moisture in the leaves. This process rolls the leaves by pressing under a rotating disk to bring the moisture from the center of the leaves to the surface. The process is conducted at room temperature for 24 minutes.
• Next, the leaves go to another rolling/drying machine, which uses a spinning pedal inside of a revolving drum to convert the leaves into a round shape. This process takes about 40 minutes. It is very important to take out the leaves at the same moisture level every time.
• The tea leaves are removed from the previous machine, separated into small portions and placed in pots. They are gradually rolled into tiny round or needle shapes using a weight. This step takes 40 minutes and removes most of the moisture. The total process thus far takes about three hours compared to hand rolling and heating which can take up to 10 hours.

Final drying

• In Japan, green tea must be dried for about 30 minutes after the final rolling step for storage. The tea is spread on a caterpillar-type device and dried slowly to about 5% moisture content or less. At this stage the half-processed tea, called aracha, is shipped to tea merchants or wholesalers for final processing. Aracha is not uniform in size and still contains stems and dust.

Post-processing

• After the tea is shipped to the wholesalers in Japan, it undergoes several other steps to produce the final product. A special machine grades and cuts the tea by particle size, shape, and cleanliness, depending on the final qualities desired. The machine uses mechanical sieves or sifters fitted with meshes of appropriate size, as well as cutting devices to achieve a quality tea. Another drying step follows to produce the aromatic flavor, followed by blending per customer's specifications, packing and finally shipping to retail shops. In other countries, similar sorting, weighing, and packaging steps occur after the shaping process.

Quality Control

The quality of green tea depends first on using good tea leaves. The natural quality of the leaf, including color and aroma, must then be preserved during the manufacturing process to produce a good green tea. In Japan, this involves controlling the temperature to 93.2-96.8° F (34-36° C) during rolling, drying, and storage. Since tea leaves can generate their own heat, cool air is blown into the bottom of the container to keep the leaves at the proper temperature during storage.

The Japanese government also subjects all exported tea to a strict inspection. Standard samples, which are established at the beginning of the tea season each year, are used to compare various properties of the finished product with the samples. Leaves, stems, moisture, content, flavor, taste, and color are all rigidly examined. There is also a stringent chemical analysis to determine tannin, caffeine, vitamin, and mineral contents. Tea is exported only after passing these tests.

The Future

Though the health benefits of green tea have been known for centuries, recent research is providing concrete evidence of these benefits. Studies have shown that green tea can prevent cancer since it contains catechin, the major component of tea. A study in Japan showed that residents in areas devoted to green tea production in the central and western regions of Shizuoka Prefecture, who drink the tea daily, have a significantly lower death rate for all types of cancer compared to other regions.

These findings were supported by animal experiments that showed green tea reduced the growth of tumors. Other research has shown that green tea consumption may inhibit nitrosamine formation—known carcinogens or cancer-causing chemicals.

Green tea catechin has also been shown to limit the excessive rise in blood cholesterol in both animals and humans, as well as prevent high blood pressure. Other benefits of catechin include killing bacteria and influenza viruses, preventing halitosis, inhibiting increase of blood sugar, and fighting cariogenic bacteria. Green tea (especially matcha) also contains important vitamins (C, B complex, and E), fluoride (for preventing cavities), amino acids (for lowering blood pressure), and polysaccharides (lowers blood sugar). Green tea is a strong antioxidant as well and is even more powerful than vitamin E or vitamin C due to the presence of polyphenols, such as epigallocatechin gallate (EGCG).

Extracts of green tea may also make strains of drug-resistant bacteria that cause skin infections more sensitive to penicillin, British researchers report. The investigators also found that diluted tea extract acted synergistically with antibiotics, making them more potent against particular strains of this type of bacteria.

In addition to preventing or curing these more common diseases, preliminary research indicates the antiviral capability of green tea catechin may have some beneficial effect in fighting AIDS. Laboratory tests have verified that catechin can inhibit the activity of the AIDS virus. Instead of simply being known as a popular Japanese beverage, green tea may thus become an important "new" medicine of the twenty-first century for the entire world.

Where to Learn More

Books

Mitscher, Lester A. and Victoria Dolby. The Green Tea Book: China's Fountain of Youth. Avery Publishing Group, 1997.

Oguni, Dr. Itaro. Green Tea and Human Health. University of Shizuoka, Japan Tea Exporters' Association.

Okakura, Kakuzo. The Book of Tea. Dover Publications Inc., 1964.

Rosen, Diana. The Book of Green Tea. Storey Books Inc., 1998.

Other

Japan Tea Exporter's Association. 17 Kitabancho, Shizuoka, Japan 420-0005. +81-54-271-3428. Fax: +81-54-271-2177.

Maruichi Green Tea Farm. http://www.maruichi-jp.com (February 2, 1999).

The Teaman's Tea Talk. http://www.teatalk.com (June 30, 1998).

The Teapot Salon. http://www.iris.orjp/-hamadaen/ (1996).

[Article by: Laurel Sheppard]

Chemical formula:

Green Tea oral dosage forms

What is Green Tea?

GREEN TEA is a dietary supplement (herbal remedy). Proposed health uses for green tea include protective effects against cancer and heart disease. Some promote green tea for weight loss. Green tea is not FDA-approved. Green tea usually contains caffeine, but some green tea products are decaffeinated. Seek the advice of their health care professional prior to taking green tea regularly for health purposes.

What should I tell my health care provider before I take this medicine?

It is important for you to tell your prescriber or other health care professional that you are using green tea. Some herbs exert potent effects and may interact with other drugs you are taking.

You should discuss green tea with your health care professional BEFORE taking it if you have any of these conditions:
• abnormal bleeding or a history of bleeding
• anemia
• diabetes mellitus
• heart disease or irregular heartbeat
• high blood pressure
• kidney disease
• liver disease
• low blood sugar
• seizure disorder
• stomach disorders such as ulcers or heartburn
• taking blood-thinning medications
• thyroid disease
• trouble sleeping
• an unusual reaction to Green Tea, caffeine, other medicines, foods, dyes, or preservatives
• pregnant or trying to get pregnant
• breast-feeding

How should this medicine be used?

Green tea is usually taken by mouth (i.e., swallowed), either as a beverage or in capsule or tablet form. Follow the directions on the package label or talk to your health care provider.

Contact your pediatrician or health care professional regarding the use of this medicine in children. Special care may be needed.

What if I miss a dose?

If you miss a dose, simply resume taking it on your previous schedule. Do not take double or extra doses to catch up, however.

What drug(s) may interact with Green Tea?

• aspirin
• cilostazol
• cimetidine
• ciprofloxacin
• clarithromycin
• clopidogrel
• clozapine
• creatine
• danshen
• dipyridamole
• disulfiram
• enoxaparin or other injectable blood thinners
• ephedra, Ma huang
• epinephrine
• erythromycin
• female hormones, like estrogen or birth control pills
• feverfew
• fluconazole
• fluvoxamine
• garlic
• ginger
• ginkgo biloba
• guarana
• iron
• isoproterenol
• ketoconazole
• lithium
• medicines for colds and breathing difficulties
• medicines for high blood sugar or diabetes
• medicines for sleep
• medicines for weight loss
• medicines called MAO inhibitors-phenelzine, tranylcypromine, isocarboxazid, selegiline
• methyldopa
• mexiletine
• phenobarbital
• phenytoin
• rifampin
• stimulants like amphetamine, dextroamphetamine, methylphenidate
• tacrine
• terbinafine
• theophylline
• ticlopidine
• warfarin

For many herbs, interactions with other medications are unknown. That is why you should always be careful when mixing herbal remedies with traditional medications. If you take any other medications, consult with your health care professional prior to taking green tea.

Tell your prescriber or health care professional about all other medicines you are taking, including non-prescription medicines, nutritional supplements, or herbal products. Also tell your prescriber or health care professional if you are a frequent user of drinks with caffeine or alcohol, if you smoke, or if you use illegal drugs. These may affect the way your medicine works. Check with your health care professional before stopping or starting any of your medicines.

What should I watch for while taking Green Tea?

Since green tea is derived from a plant, allergic reactions are possible. Stop using this herb if you develop a rash. You may want to see your health care professional, or inform them that this occurred.

Because green tea usually contains caffeine, do not take green tea close to bedtime. It may prevent you from sleeping.If you have been a regular caffeine user, you can get withdrawal symptoms if you stop taking caffeine. Symptoms include tiredness, dizziness, headache, anxiety, or nervousness. If you are taking a green tea product that contains caffeine, be aware of other products that contain caffeine, like coffee, black or oolong tea, colas, chocolate and some medications.

If you are scheduled to have surgery, let your health care provider know you are using green tea.

What side effects may I notice from receiving Green Tea?

Side effects that you should report to your prescriber or health care professional as soon as possible:
• anxiety or panic reactions
• bleeding (gums, nose, skin, stool, urine)
• confusion
• dizziness, lightheadedness, or fainting spells
• fast or irregular breathing or heartbeat (palpitations)
• muscle twitching
• nausea and vomiting
• seizures (convulsions)
• trembling
• unusual bruising

Side effects that usually do not require medical attention (report to your prescriber or health care professional if they continue or are bothersome):
• constipation
• difficulty sleeping
• diarrhea
• frequent passing of urine
• headache
• irritability
• nervousness, restlessness
• stomach upset
Most of the common side effects of green tea are from caffeine. Reduce your intake of green tea or change to a decaffeinated product if you get any of these side effects.

Where can I keep my medicine?

Keep out of the reach of children in a container that small children cannot open.

Follow the package label for directions on storage. Throw away any unused medicine after the expiration date.

GENERAL INFORMATION REGARDING DIETARY SUPPLEMENTS:
Dietary supplements include amino acids, vitamins, minerals, herbs, botanicals, and other plant-derived substances, and extracts of these substances. These products are easy to identify as they must state 'Dietary Supplement' on the label. A 'Supplement Facts' panel is provided on the label for most products. Supplements are not drugs and are not regulated like drugs. You should note that rigid quality control standards are not required for dietary supplements. Big differences in potency and purity of these products can occur. Scientific data to support the use of a dietary supplement for a certain disease or ailment may not be available. This product is not intended to diagnose, treat, cure or prevent any disease.

The Food and Drug Administration suggests the following to help consumers protect themselves:
• Always read product labels and follow directions.
• 'Natural doesn't mean a product is safe for humans to take.
• Look for products containing ingredients with the 'USP' notation. This indicates the manufacturer followed the standards of the US Pharmacopoeia.
• Supplements produced or distributed by a nationally known food or drug company are more likely to be made under tight controls as these companies have standards in place for their other products. You can write to the company for more information about how the product was made.

Last updated: 9/21/2004 2:13:00 PM

Important Disclaimer: The drug information provided here is for educational purposes only. It is intended to supplement, not substitute for, the diagnosis, treatment and advice of a medical professional. This drug information does not cover all possible uses, precautions, side effects and interactions. It should not be construed to indicate that this or any drug is safe for you. Consult your medical professional for guidance before using any prescription or over the counter drugs.

Description

Green tea is produced from the leaves of the Camellia sinensis, or tea plant. Oolong and black tea are also produced from the plant, but are processed and oxidized in different manners. Of the three, green tea contains the highest levels of polyphenols, the antioxidant substance that is believed to be beneficial in protecting against both cancer and atherosclerosis.

The tea plant is actually a variation of evergreen bush, with glossy green leaves and small white to pink flowers. The plants can reach a height of 30–40 ft (9–12 m) or taller in the wild, but are generally kept to a height of 6 ft (1.2 m) or less on the tea plantations and gardens where they are grown in China, Argentina, Japan, India, Indonesia, Kenya, Malawi, Sri Lanka, Turkey, Pakistan, Bangladesh, and Tanzania. Tea plants are cultivated in countries where warm, rainy growing conditions are abundant, and are also frequently grown in high altitude areas.

When tea plants reach maturity at three or four years of age, the young leaves and leaf buds—the parts of the plant highest in polyphenols—are harvested. Green tea is produced by steaming or roasting the leaves as soon as they are picked, and then rolling and drying the tea leaves to remove any moisture.

General Use

Approximately 2.5 million tons of tea are grown and produced worldwide on an annual basis. Written records date the use of the plant as a beverage since at least the tenth century B.C. in China, and it is thought to be close to 5,000 years old. Tea is the most consumed beverage worldwide (after water). It is also one of the most popular herbal infusions in existence—drunk regularly by over half the world population.

The polyphenols in green tea that act as antioxidants may actually inhibit the growth of existing cancer cells. In some animal studies, injections of tea extracts reduced the size of cancerous tumors in animals. The active agent that is thought to have this effect is an antioxidant, epigallocatechin-3-gallate (EGCG).

Recent clinical studies have also indicated that regular use of green tea may reduce the risk of certain types of cancer, including oral, skin, prostate, colon, stomach, and rectal. In one clinical trial, patients with pre-cancerous mouth lesions who were treated with green and black tea extracts achieved a 38% decrease in the number of pre-cancerous cells. Late in 2001, researchers acknowledged one reason for green tea's anticancer effect, but further human studies are needed to clearly define its role in cancer prevention.

The antioxidants in green tea may also be helpful in lowering cholesterol and preventing hardening of the arteries and ischemic heart disease. Low flavonoid intake has been linked to atherosclerosis in several studies. The data from one 1999 study, which followed more than 3,400 tea-drinking residents of Rotterdam, the Netherlands, concluded that regular, long-term tea consumption can have a protective effect against severe atherosclerosis.

Another preliminary study published in 1999 in the American Journal of Clinical Nutrition found that green tea extract may increase energy levels and promote fat oxidation, and consequently, may be a useful tool in weight control. A recent study, reported on in early 2002, showed that topically applied green tea extracts can reduce harmful effects of radiation from the sun. Further study might show that green tea polyphenol applications can help prevent sunburns.

In addition to polyphenols, green tea contains several minerals, including fluoride and aluminum. The fluoride in green tea may be useful in fighting tooth decay. Green tea is also an antibacterial agent, and can help to prevent gingivitis and periodontal disease by killing E. coli and streptococcus bacteria. This antibacterial action can also be effective in treating halitosis, or bad breath, by killing odor-causing bacteria.

As an herbal remedy, green tea is often recommended to ease stomach discomfort, vomiting, and to stop diarrhea. The antibacterial action of tea is useful in treating infections and wounds.

Preparations

Green tea leaves and tea bags can be purchased at most grocery, drug, and health food stores. It is graded by leaf size, with tea containing whole leaves and leaf tips considered the highest quality tea. Tea grades include Broken Orange, Pekoe, Broken Pekoe Souchong, Broken Orange Pekoe, Fannings, and Dust.

Although green tea is grown from a single plant, slight variations in tea processing (usually in the way the tea is rolled) have created a number of varieties of green tea. Popular green tea varieties include Gunpowder, Hyson, Dragonwell, Sencha, and Matcha.

Tea leaves should be kept in an air-tight container to retain flavor and prevent odors and moisture from being absorbed by the tea. It should also be stored in a cool place for no longer than six months before use.

The most common method of preparing green tea is as an infusion. The tea is mixed with boiling water, steeped for several minutes, and then strained or removed from the infusion before drinking. Approximately two teaspoons of loose tea, or a single tea bag, should be used for each cup of boiling water. A strainer, tea ball, or infuser can be used to immerse loose tea in the boiling water before steeping and separating it.

A second method of infusion is to mix loose tea with cold water first, bring the mixture to a boil in a pan or teapot, and then separate the tea from the infusion with a strainer before drinking.

Flavonoids—polyphenols with antioxidative properties—are released into the infusion as the tea steeps. The longer the steeping time, the more flavonoids are released by the tea leaves, although most will infuse into the water during the first five minutes of brewing. Longer steeping time also results in a higher caffeine content in the brewed tea.

Green tea leaves can be used in a poultice for treating insect bites and other skin irritations. Green tea leaves are chopped and boiled in water for two to three minutes. After the excess water is squeezed from the leaves, the green tea is applied to the area to be treated and wrapped in a bandage. Green tea also makes an effective astringent, and tea-soaked cloth or tea leaf poultice may help renew tired and puffy eyes.

The antibacterial activity of green tea also makes it appropriate for use in compresses for cuts and abrasions. A quick compress can be made by soaking a pad or bandage in hot tea, wringing out the excess fluid, and holding the pad firmly against the wound. Once the compress cools, the process can be repeated.

Precautions

The U.S. Food and Drug Administration (FDA) includes tea on their list of "Generally Recognized As Safe" substances. However, pregnant women and women who breast feed should consider limiting their intake of green tea because of its caffeine content. Tea can pass into breast milk and cause sleep disorders in nursing infants. Decaffeinated green tea is available that contains only trace amounts (5 mg or less) of caffeine. Women should check with their healthcare professional about drinking tea when pregnant or nursing.

Tea can stimulate the production of gastric acid, and individuals with ulcers may want to avoid drinking green tea for this reason. Those taking warfarin or any blood-thinning drugs should first consult with the physicians before consuming green tea, as it may counter the effects of the drug.

Side Effects

Green tea contains caffeine, a central nervous system (CNS) stimulant that can cause restlessness, irritability, difficulty sleeping, tremor, heart palpitations, loss of appetite, and upset stomach. To avoid side effects, caffeine intake should be limited to 300 mg or less a day (the equivalent of 4–8 cups of brewed hot tea). Caffeine-free green tea preparations are available commercially.

The tannin in tea can cause nausea when drunk on an empty stomach and inhibit the absorption of nonheme iron. Individuals with iron-deficiency anemia who take iron supplements should avoid drinking green tea several hours before and after taking supplements. Iron absorption with tea can be increased by consuming foods rich in vitamin C with tea, such as a slice of lemon.

Resources

Books

Mitscher, Lester A., and Victoria Dolby. The Green Tea Book. New York: Penguin Putnam, 1998.

Rosen, Diana. The Book of Green Tea. Pownal, VT: Storey, 1998.

Periodicals

"Anticancer Mechanism of Green Tea Identified." Cancer Weekly (January 1, 2002): 16.

Bates, Betsy. "Green Tea Extract May Help Prevent Sun Damage (Potential Chemopreventive Agents)." Skin and Allergy News (January 2002): 30.

Dulloo, Abdul G., et al. "Efficacy of a Green Tea Extract Rich in Catechin Polyphenols and Caffeine in Increasing 24-h Energy Expenditure and Fat Oxidation in Humans." American Journal of Clinical Nutrition (December 1999): 1040–1045.

Geleijnse, Johanna M., et al. "Tea Flavonoids May Protect Against Atherosclerosis: The Rotterdam Study." Archives of Internal Medicine 159 (October 11, 1999): 2170–2174.

Hertli, Peter. "Green Tea and Blood Thinners Don't Mix (Mailbag)." Prevention (March 2002): 24.

Mukhtar, H., and N. Ahmad. "Green Tea in Chemoprevention of Cancer." Toxicological Sciences 52 (December 1999): 111–7.

[Article by: Paula Ford-Martin; Teresa G. Odle]

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