If preliminary findings stand up to closer scientific scrutiny, tea -- especially the green tea of the Far East -- could become a popular and potent weapon in the war against chronic diseases.
Experts from around the world spent two days last week describing a laundry list of the potential benefits of tea, from preventing tooth decay to thwarting cancer. According to their reports, presented in New York at the first international symposium on the health effects of tea, it contains various substances that may lower blood pressure and blood cholesterol levels, stabilize blood sugar, kill decay-causing bacteria, block the action of many carcinogens and inhibit the growth of cancerous tumors.
Indeed, one scientist, Dr. Harold N. Graham, retired director of research for the Thomas J. Lipton Company, predicted, "Once we determine which components of tea are most useful pharmaceutically, it should be possible to produce teas that are highly beneficial and still pleasing to people." He said it might even be possible to enrich other foods with the biologically active substances in tea.
Studies and Observations
The symposium was jointly sponsored by the American Health Foundation, an independent nonprofit research organization that focuses on the relationship between habits and health, and two groups that represent the tea industry, the Tea Council of the U.S.A. Inc. and the Tea Association of the U.S.A. Inc.
Most of the suggested health benefits of tea have emerged from studies in laboratory animals and cell cultures, although some are supported by observed disease rates among tea-drinking people in various countries. For example, Japanese people who are heavy consumers of green tea have lower death rates from cancer of all types and especially cancer of the stomach, a major killer in Japan.
Coffee-drinking Westerners are generally surprised to learn that, after water, tea is the world's most popular beverage. Nearly four-fifths of the tea produced is so-called black tea in which the tea leaves are broken up and exposed to air to oxidize the chemicals known as polyphenols, which are the main biologically active ingredients of tea.
About one-fifth of the tea drunk worldwide is green tea. The tea leaves are stabilized by moist or dry heat, which destroys the enzyme polyphenoloxidase and prevents oxidation of polyphenols. About 2 percent of tea consumed is oolong, in which the polyphenols are only partially oxidized.
Caffeine Is Not a Problem
Although there has been some public concern about the health effects of tea because of its caffeine content, researchers at the symposium said this popular drug was of minimal health consequence to most consumers. On average, brewed tea contains about half the caffeine found in coffee.
Dr. Arthur Bassett, pharmacologist at the University of Miami School of Medicine, said the average American tea drinker ingests about 80 to 100 milligrams of caffeine a day and coffee drinkers take in twice that. At these levels, he said, there was no evidence that caffeine and related compounds caused or promoted the growth of cancer or damaged the heart.
Although caffeine can produce slight increases in blood pressure, most regular consumers rapidly become resistant to this effect, Dr. Bassett said, adding that only a small percentage of patients with high blood pressure may be adversely affected by caffeine intake.
To date, most of the studies of the health effects of tea have involved extracts of green tea, the predominent form consumed in Japan and a popular tea in China as well. The extracts are rich in polyphenols, the substances that Dr. Graham said make up the "guts" of tea, accounting for up to 40 percent of tea's dry solids. But teas can vary widely in amounts of polyphenols and other compounds.
They Are Talking Real Tea
The chemical composition of a cup of tea depends not only on the type but also the genetic variety, where and how it was grown, how it was processed and how it was brewed. The researchers emphasized that their findings pertain only to real tea from the plant known scientifically as Camellia sinensis, not the so-called herbal teas, which can be made from scores of other plants and may contain few or none of the active compounds under study.
It is not yet known whether the oxidized polyphenols in black tea -- the kind most Westerners consume -- have the same actions in the body as the unoxidized polyphenols in green tea.
In several studies with laboratory animals, polyphenols have been shown to inhibit the activation of many common cancer-causing chemicals, thus preventing prevent these agents from transforming normal cells into cancer cells.
Dr. Fung Lung Chung of the American Health Foundation reported that mice given green tea or one of the polyphenols derived from it in their drinking water developed considerably fewer lung tumors after being exposed to a cancer-causing nitrosamine from tobacco smoke.
Tumors Reported Prevented
In studies in rats exposed to a different nitrosamine, Dr. Junshi Chen of the Chinese Academy of Preventive Medicine in Beijing showed that two Chinese teas -- Fujian oolong and jasmine -- inhibited the development of esophageal tumors. Other experimenters working with laboratory animals reported beneficial effects of green tea extracts in warding off skin cancer, inhibiting the proliferation of pre-cancerous cells, and even in protecting arteries against the damage caused by high-fat diets.
The potential benefits of tea must now be tested in people under carefully controlled experimental conditions. It could be that people who choose to drink tea are inherently healthier or have different health-influencing habits than people who drink coffee or other beverages.
Testing these laboratory findings in human populations is difficult because it is hard to find a "clean" group for comparison: Most people drink either tea or coffee. Hence tea drinkers, in epidemiological studies, are often compared with coffee drinkers and such studies have to be interpreted with particular caution.
Most experts at the conference believed it is premature to recommend tea for its purported anticancer effects. Dr. Allan H. Conney of Rutgers University College of Pharmacy said the relevance to humans of the laboratory findings needed further study as well as the side-effects of drinking large amounts of green tea. Some commercial producers echoed the caution.
But others were less reluctant to push tea as a possible panacea. Dr. Yukihiko Hara, a food scientist for the Mitsui Norin Company in Fujieda City, Japan, said that 25 years of research with animals had convinced him that tea is a health-promoting and life-prolonging beverage.
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