September 7, 1999
By JANE E. BRODY
Coffee lovers, take heed. For the sake of your health, you might consider switching at least some of those daily cups of java for tea. Not herbal tea but "real" tea -- green tea, black tea, Chinese tea, fruit-flavored tea, with or without caffeine, lemon, milk or sugar.
As long as the leaves come from the plant Camellia sinensis, tea will contain potent antioxidant chemicals that have been linked to protection against major diseases like cancer and heart disease. Even the caffeine in tea may be somewhat beneficial, emerging evidence suggests.
The popularity of tea in Japan and China may partly explain why heart disease rates are so much lower in the Far East than in Western countries.
The Truths of Tea
There are three types of real tea: green, black and oolong. Green tea, which is most popular in Japan and China, has in recent years found a small but growing following here as word about its potential health benefits has leaked out. It is the least processed of all the teas, made by quickly steaming or heating the leaves of Camellia sinensis.
Black tea, by far the most popular in Western countries and India, is prepared by exposing tea leaves to air. That exposure causes oxidation, which turns them a deep brown and intensifies their flavor. The leaves are then crushed. According to Dr. Gary Beecher, food chemist with the United States Department of Agriculture, black tea contains as much of the protective chemicals as green tea, though the form may differ.
Oolong is between the two: more processed than green tea but less so than black tea. It is exposed to heat, light and crushing for less time than black tea.
Herbal teas, on the other hand, come from a wide variety of plants other than the tea plant and may include roots and flowers as well as leaves. Most herbal teas do not possess the antioxidant properties of real tea, although they may contain certain other biologically active compounds. A few also contain caffeine.
Contrary to common belief, green tea has as much caffeine as black tea, though all teas have less caffeine than drip-brewed coffee. A typical eight-ounce cup of tea prepared from one tea bag brewed for three to five minutes contains 40 milligrams of caffeine, compared with 100 milligrams in a cup of brewed coffee.
The caffeine content of tea can range from 20 to 90 milligrams a cup, depending on the blend of tea leaves, method of preparation and length of brewing time, whereas a cup of coffee may contain from 60 to 180 milligrams of caffeine. Decaffeinated tea, like decaffeinated coffee, has about 4 milligrams of caffeine per cup.
Instant teas and prepared iced teas, which can be purchased with or without caffeine, may be too highly processed to contain much of the protective chemicals.
Throughout the 1990's researchers exploring the health effects of tea have gradually accumulated highly suggestive, though not definitive, evidence for tea's ability to prevent or ameliorate several common serious diseases.
Making It Healthy
Most of the presumed health effects are related to polyphenols, chemicals that act as antioxidants, preventing cell damage caused by highly reactive molecules called free radicals. The polyphenols in tea, especially green tea, are more potent antioxidants than well-known antioxidants like vitamins C and E, experts say.
The bulk of evidence for tea's health benefits comes from studies in animals that were treated with amounts of tea polyphenols equivalent to what might be consumed by a regular tea drinker.
For example, in a study published in April, a research team from Case Western Reserve University School of Medicine added green tea polyphenols to the drinking water of 18 mice and none to the water of 18 other mice. All the animals were then injected with a substance that causes a condition like rheumatoid arthritis in people. Of the group that got the polyphenols, only eight developed arthritis; in the group that got plain water, all but one developed arthritis.
With regard to cancer, several dozen animal studies indicate that the polyphenols and related compounds in tea are protective, especially against cancers of the oral cavity and digestive tract. Tea chemicals are believed to act by preventing damage to DNA that could result in a loss of control over cell growth.
According to cancer researchers at Rutgers University College of Pharmacy, "Tea is one of the few agents that can inhibit carcinogenesis at the initiation, promotion and progression stages." However, they added, it is not yet known how effective tea can be in preventing human cancer, what dose is most effective or what is the best way to administer the active compounds.
Studies in people have yielded inconsistent results, in part because in some studies other factors may have entered into the picture to distort the findings, like the heat of the tea and the use of tobacco or alcohol. In one well-designed study conducted in Beijing, China, among 59 patients with precancerous mouth lesions, those treated for six months with capsules of oxidized green tea polyphenols experienced a decrease in the size of the lesions; in the untreated group, the lesions got larger.
A study of more than 35,000 postmenopausal women in Iowa suggested that women who drank two or more cups of tea daily were less likely to develop cancers of the digestive tract and urinary tract. However, no protection was found against other cancers.
Likewise, a study in the Netherlands among 58,000 men and 62,000 women found no link between tea drinking and a reduced risk of cancers of the lung, breast or colon. However, in a study in laboratory mice and rats, Dr. Fung-Lung Chung of the American Health Foundation found that both green and black tea and caffeine given in drinking water protected the animals against lung cancer caused by a major carcinogen in tobacco.
Another study in mice showed that both green and black tea inhibited the growth of both malignant and nonmalignant skin tumors. And a study in rats conducted by Dr. Roderick H. Dashwood of Oregon State University showed that both green and black tea inhibited the formation of precancerous lesions in the colon.
With regard to heart disease and stroke, a study of 1,330 Chinese men found a significantly lower level of serum cholesterol and triglycerides among those who drank more than 10 cups of green tea a day.
Some studies in Western countries have indicated that tea drinkers may be less likely to develop heart disease and stroke.
A Harvard study by Dr. Howard Sesso indicated that people who drank one or more cups of black tea a day were half as likely to suffer a heart attack as those who did not drink tea, regardless of other risk factors for heart disease.
However, much more research is needed to sort out the effects of tea on blood vessel diseases as well as cancer. For example, in a study of 880 Japanese men, researchers found that heavy tea drinkers were also likely to eat more fruits and vegetables, which may account for or contribute to their lower risk of heart disease and cancer.
Still, the evidence to date is sufficiently suggestive to prompt the National Cancer Institute to conduct studies of the capacity of the biologically active chemicals in green and black tea to curb the development of cancer in people at high risk for developing cancers of the colon, lung, esophagus and skin.
And Japanese researchers have suggested that the ability of green tea
and its chemicals to inhibit a substance called tumor necrosis factor-alpha
may make it useful in treating a wide range of health problems that include
Crohn's disease, multiple sclerosis, malaria and sepsis as well as rheumatoid