Tea Chronicles
s legend has it, was discovered in 2737 B.C. by Chinese Emperor Shen-Nung. According to the story, he was boiling a pot of water outside when some leaves from a wild tea bush accidentally fell into the pot. After tasting the strange, new brew the Emperor took an instant liking to it.
The earliest mention of tea in Chinese literature appeared in The Classics of tea, writtten sometime around 350 A.D. by Lu Yu, in which he described the cultivation, processing and use of tea. By the 9th century A. D., tea was growing in Japan after being introduced by Chinese Buddhist monks.
Gradually, tea culture spread to Java, the Dutch East Indies, and other tropical and sub-tropical regions. It became a popular trade item, as in 1389 when China's Imperial Tea and Horse Commission bartered approximately one million pounds of tea to nomads in exchange for some 20,000 horses. In the 16th century, European traders introduced their fellow countrymen to a unique oriental begerage called tea, and by the 18th century England was importing about 100,000 pounds of tea per year. In fact, by that time the brew had become the national beverage in England.
Tea eventually became popular in America, but in 1767 the British government placed a tax on the tea consumed by the colonists. This resulted in the famous Boston Tea Party in 1773, and was a contributing factor in the Revolutionary War.
The popularity of the beverage grew world-wide. In France, physicians tending King Louis XIV claimed that tea cured royal headaches. The Greeks regarded tea as "the divine leaf" which cured asthma, colds, and bronchitis. In the 19th century, Russian scientists called tea "the elixir of life" and expounded upon its ability to aid digestion and improve cardiovascular health.
Ever the innovative country, the U.S. is responsible for several creative changes involving tea. For instance, a New York City merchant by the name of Thomas Sullivan sent samples of his tea to customers in small silk bags, beginning the introduction of the tea bag back in 1904. Later, in 1948, an impatient American invented and marketed instant tea.
Today, over 3,000 varieties of teas are available from such places as China, Japan, Taiwan, India, Sri Lanka, Indonesia, Africa, New Guinea, South America, Turkey, Argentina and Russia. Aside from plain water, tea is the most widely consumed beverage in the world.
Good 'N Green
While a wide variety of herbs are currently used for making tea, for "regular" tea there is only one kind of tea plant, known as Camellia sinensis. The tea plant is an evergreen shrub (occasionally growing to tree size) with many branches. The leaves are dark green and roundish, with the young leaves being rather hairy. Its flowers are white and usually solitary.
There are three basic types of regular tea; green, black, and oolong. All three types of tea come from the same tea plant; the differences in the teas are a result of processing methods. The part of the tea plant used in making any tea is the leaf bud and the two adjacent young leaves along with the stem, broken between the second and third leaf. Older leaves are considered inferior and are often the stuff of instant teas. The young leaves and leaf bud are called "tea flush" and are collected from spring until fall.
Black tea is made by withering, rolling, fermenting, and drying the leaves. Green tea is made by steaming and drying. The leaves aren't permitted to ferment and oxidize as in black tea, thereby preserving many more nutrients - particularly the polyphenols. Oolong tea is allowed to partially oxidize.
Of the 2.5 million tons of dried tea produced each year, only 20 percent is green tea. In other words, nearly four times as much black tea is produced and consumed as compared to green tea. India and Sri Lanka are the major producers of black tea, while green tea is produced and consumed chiefly in China, Japan, and a few countries in North Africa and the Middle East. Taste, rather than nutrient content, is credited for the higher demand for black tea. Polyphenols have a strong taste, and as black tea has only about half the polyphenol content of green tea, it also has a milder flavor.
Polyphenols and Other Constituents
Green tea contains many nutrients, but the primary nutritious constituents are the polyphenols. The term polyphenol denotes the presence of multiple phenolic rings in the chemical composition. The chief polyphenols in green tea are flavonoids such as catechin and proanthocyanidins, with the four major polyphenols being epicatechin. epicatechin gallate, epigallocatechin, and epigallocatechin gallate. Of the four, epigallocatechin gallate is regarded as the most significant active constituent.
Other compounds found in green tea include an unusual amino acid calledtheanine, caffeine, tannins, lignin, organic acids, protein, sugars, and chlorophyll.
Polyphenols are everywhere. Some give plants their color, while others give plants their taste. The strong, astringent flavor of tea is attributed to its polyphenol content. Polyphenols are potent antioxidants. In fact, these special flavonoids have been credited with having more potency than vitamins C and E. Polyphenols appear to thwart cancer by at least three methods: They can shut off the formation of cancer cells; turn up the body's natural detoxification defenses, and suppress cancer advancement.
Pharmacology
It's no secret that the most beneficial health aspect to consuming green tea is its apparent cancer fighting properties. Most of the population and experimental studies on green tea have focused on its cancer-protective features. The polyphenols in the brew are not only potent antioxidants themselves, but they also seem to increase the activity of antioxidant enxzymes. According to a laboratory study conducted by S.G. Khan and published in Cancer Research, mice were fed green tea ployphenols via their drinking water for 30 days. The researchers noted a significant increase in the activity of antioxidant and detoxifying enzymes; specifially, glutathione peroxidase, glutathione reductase, glutathione S transferase, caralase, and quinone reductase. This increase in activity was observed in the small intestive, liver, and lungs.
In vitro studies also support green tea's cancer-preventive properties. For instance, in the Japanese Journal of Clinical Oncology a study by A. Komori was published concerning green tea's relationship with breast cancer. Komori found that green tea inhibited the growth of mammary cancer cell lines. The fundamental mode of action of polyphenols seems to be to inhibit the interaction of tumor promoters, hormones, and growth factors with their receptors, resulting in a sort of sealing-off effect.
Green tea polyphenols suppress cancer cell formation and growth by blocking the formation of cancer-causing agents such as nitrosamines, quelling the activation of carcinogens, and detoxifying or trapping cancer-causing compounds. Consuming green tea with meals may inhibit the formation of nitrosamines. These cancer-causing, nitrate by-products are formed when nitrates, such as those employed in the curing of bacon and ham, bind to amino acids. Laboratory and clinical trials have demonstrated green tea polyphenols suppress the formation of nitrosamines in both animals and humans. For instance, researcher H.F. Stich noted in Preventive Medicine that when human volunteers consumed green tea along with 300 milligrams of sodium nitrate and 300 milligrams of proline, the formation of nitrosoproline (a potent nitrosamine) was virtually blocked.
Chemopreventive Applications
While green tea is certainly not a panacea for all types of cancer, it does seem to target specific cancer types in its preventive and therapeutic role. These include cancers of the gastrointestinal tract, including those of the stomach, small intestine, pancreas, and colon; lung cancer, esophageal cancer, and estrogen-related cancers including the majority of breast cancers, as observed in both animal and human models.
Yu Tang Gao and other researchers at the Shanghai Cancer Institute in the People's Republic of China, and Joseph K. McLaughlin, Ph.D., and colleagues at the National Cancer Institute in Bethesda, Maryland, reported in the Journal of the National Cancer Institute on green tea's ability to protect against cancer of the esophagus.
The study involved 902 patients, aged 30 to 74, who were diagnosed with cancer of the esophagus from October of 1990 through January of 1993. A group of 1,552 healthy volunteers were used as controls. Histories of cancer in the family, diet, smoking and drinking habits were taken into account.
The researchers found that for those who refrained from smoking or drinking alcohol, green tea comsumption reduced the risk of esophageal cancer in men by 57 percent, and 60 percent in women. Unfortunately, for those who smoked, drank alcohol, or consistently drank extremely hot soups, green tea exerted little protection.
Benefits Continue To Brew
In addition to its chemopreventive properties, green tea polyphenols exert other healthy attributes within the body. They exercise antimicrobial activity, and appear to be particularly useful in the treatment of intestinal disorders such as cholera and typhus. In a number of preliminary studies, any viruses seem to be adversely affected by the presence of polyphenols. In fact, green tea may be worthwhile investigating in regards to its effect on the AIDS virus, as its polyphenols increase the percentage of T-helper lymphocytes and decrease the precentage of T-suppressor lymphocytes, while HIV infection decreases T-helper, and increases T-suppressor, lymphocyte activities.
A number of studies also indicate that green tea can aid in the fight against atherosclerosis and hypertension. The polyphenols not only lower serum LDL cholesterol levels, but when consumed in high quantities (10 cups per day), raise HDL levels and lower triglyceride levels, as well. In laboratory trials, a reduction in blood pressure was noted in mice after polyphenols were introduced into their diets. In addition, in preliminary laboratory trials polyphenols exhibit anti-inflammatory properties.