Reading the Tea Leaves


Farmers near Bandung, Indonesia, picking tea leaves. (Joanna B. Pinneo)


Camellia sinensis

What it does: Green tea contains chemicals that fight bacteria and cancer formation; some studies show that it helps prevent oxidation of low-density lipoprotein (LDL), which otherwise can lead to heart disease.

How we know: Test-tube, animal, and some human studies show that polyphenols in green tea act as antioxidants, defending the body’s cells from damage that could lead to serious disease, including heart disease and cancer. In the United States, research is under way to determine to what extent green tea works to defend the body against disease and whether it can help people who already have diseases such as cancer.

Dosage: In the United States, early research indicates that anywhere from 1 to 4 cups of green tea a day is a good preventive dose. Studies of large groups of people indicate that 1 cup a week has helped them reduce their risk of cancer. However, these studies were based on the experiences of large groups of people who have been drinking green tea as part of their routine.

Caution: Green tea contains caffeine (but not as much as coffee), so may cause insomnia. It also acts as a diuretic. One human study shows that an increased risk of death from pancreatic cancer if more than 5 cups of green tea are consumed daily; research into this risk continues. One study shows that adding milk to green tea negates its health benefits, and other studies indicate that the tea should be made from hot, not boiling, water, to protect the esophagus from life-threatening damage.

Research points the way

It may be helpful to know that black and green tea come from the leaves of the same plant—Camellia sinensis. The difference between the two teas lie in the processing method.

Black tea, the kind most Americans drink, has some health benefits, but green tea holds even more. Research shows that the processing of black tea—leaves are “sweated,” or fermented, to darken the leaves and produce flavor—destroys some of the beneficial health consitutuents that survive in unfermented green tea. Because 80 percent of tea consumed worldwide is black tea, however, research into green tea’s benefits is fairly new, according to the National Cancer Institute.

When looking for chemicals that may help people fight disease, researchers often turn to plants, whose constituents, ­including polyphenols such as catechins and flavonoids, can potentially offer humans a wide range of health benefits. Studies show that the polyphenols in green tea—including one known as EGCG—are strong antioxidants, meaning they prevent cell damage that can otherwise lead to disease.

But just how they work and whether they will work in all humans is unknown. The scientific reports focusing on green tea’s potential to protect and/or fight against disease could fill volumes. Many of these studies are precise explorations of individual compounds within the tea, and others attempt to reach a final verdict based on the research gathered so far. Some call for more study before conclusions are drawn.

However, some landmark research stands out. It’s piqued the interest of the University of Texas Center for Alternative Medicine Research in Cancer, where a clinical study is under way to get a better understanding of green tea’s health benefits. The center is focusing on only ten herbal agents that show potential for preventing cancer, a selection based not only on research findings to date, but also on public interest, says Nancy Russell, assistant epidemiologist at the Texas center.

One reason green tea is on the center’s “top ten” list, Russell says, is a report known as the “Shanghai study,” a large-scale investigation by Columbia University and the Shanghai Cancer Institute, with the U.S. National Cancer Institute participating. That study shows that people who drink green tea once a week for six months or more have a reduced risk for rectal, colon, and pancreatic cancers, and that this reduced risk may be stronger for women than men.

The researchers, who conducted the study from 1990 to 1993 and reported their findings in 1997, note that green tea might provide protection specifically from gastrointestinal tract cancers. But they caution that further studies are needed to establish the real degree of reduced cancer risk and to discover how tea works to provide it.

Russell adds that, while this study has been pivotal in the center’s current effort to learn more about green tea and cancer prevention, many other studies add to the intrigue. Among them:Cancer protection.

Researchers from the National Cancer Institute and the Shanghai Cancer ­Institute reported in 1994 that Chinese men and women who drink a cup of green tea a week have up to 60 percent lower risk of developing esophageal cancer. They studied a total of 902 patients with cancer of the esophagus for two-and-a-half years. They interviewed the patients along with 1,552 people without the disease (the researchers’ control group) about their medical history, smoking habits, tea consumption, and other factors.

The study also shows that the temperature of the tea is important. In fact, people who drink burning hot tea and other liquids have a fivefold increase in esophageal cancer over those who don’t. The National Cancer Institute reports that studies in China and other countries have shown that such repeated thermal irritation of the esophagus may increase esophageal cancer risk.

EGCG (its long name is epigallocatechin-3 gallate) killed cancer cells in laboratory experiments, according to a 1997 report from researchers at Case Western Reserve University in Cleveland, Ohio. They say that EGCG “warns” cancer cells to die off or be killed, so the cancer cells “commit suicide”—an event known in the scientific world as apoptosis. Meanwhile, healthy cells are left unharmed.

The researchers tested EGCG on both animal and human cancer samples of skin, the lymph system, and prostate tissue. They found that one cup of green tea contains between 100 mg and 200 mg of EGCG, and suggest that drinking four cups of green tea a day should provide protection from cancer.

Last June, researchers at the Medical College of Ohio in Toledo said they had verified that green tea’s cancer-­preventing abilities come from EGCG. They found that this chemical inhibits urokinase, an enzyme crucial for cancer growth. EGCG attaches to urokinase and prevents it from invading cells and forming tumors, according to the researchers.

By 1997, scientists at the University of Texas Center for Alternative Medicine Research in Cancer had reviewed fifteen studies on green tea’s effects on humans. Eight of these studies showed that drinking green tea protects against development of esophageal, stomach, lung, colorectal, bladder, gastric, and pancreatic cancers. But two of the studies found the opposite, with one reporting an increased risk of death from pancreatic cancer if more than five cups of green tea are consumed daily.

Skin cancer protection

In animal tests conducted by the American Health Foundation and Rutgers University, researchers found that mice who consume tea are at less risk for skin cancer than those who don’t, that caffeine may have something to do with it, and that green tea is somewhat more effective than black tea.

The researchers gave groups of mice green tea, black tea, and decaffeinated versions of both types, each prepared much the same way you and I would prepare them. They also gave one group a liquid solution containing only caffeine. For two weeks, the mice had no other source of liquid. They were then exposed to ultraviolet (UV) light.

The mice drinking green tea had up to 94 percent fewer tumors per mouse compared to the control group, which received none of the solutions before UV exposure. But the mice drinking decaffeinated green tea had about as many tumors as the control group. Mice drinking black tea had 65 percent fewer tumors and, again, the decaffeinated tea had little or no effect. Those who drank the caffeine solution, prepared at a concentration comparable to the caffeine in the tea, had 53 percent fewer ­tumors.

The researchers also tested whether green tea protects against skin cancer when applied directly to the skin. After ­exposing mice to UV light, researchers ­immediately applied a caffeinated green tea extract to the backs of the mice twice a week for thirty-five weeks. The mice who received the treatment had 69 percent fewer tumors than the control group.

Pouring hot water on green tea releases its healthful constituents and ­flavor. Make sure to use hot, but not boiling, water—centuries of tea brewing have shown that hot water (158°F to 203°F) is better than boiling to bring out green tea’s flavor, and recent research shows that drinking boiling hot liquid may be harmful to the esophagus. Also, one study shows that adding milk to tea negates its health benefits.

1 teaspoon of loose-leaf green tea per cup
1 cup of water per serving, plus a little extra

Fill a kettle with cold water. Bring the water to a near boil, then pour a little into a teapot to warm the pot, swirl it around, and discard the water.

Put the tea directly into the pot or use a teaball. One teaspoon per person is the general recommendation, but adjust the amount of tea to taste.

Fill the pot with the near-boiling water. Put the lid on the pot and infuse for 10 minutes ­before serving in individual cups.

Heart protection

Researchers at Monash University in Australia reported in 1997 that Chinese and Japanese green tea prevents the oxidation of low-density lipoprotein (LDL) better than vitamin C. Oxidation of LDL plays a critical role in the development of arteriosclerosis and heart disease.

The researchers compared how equivalent concentrations of green tea, vitamin C, and vitamin E protected LDL against oxidation in a test tube. Vitamin C increased the time it took for oxidation to begin from 79 minutes to 95 minutes; vitamin E from 79 minutes to 213 minutes; and green tea from 79 minutes to 211 minutes. The researchers suggest drinking one cup of green tea daily for these benefits.

Researchers in Japan studied 1,371 men who drank green tea daily. The researchers asked the men about their living habits, including their daily tea consumption, then analyzed samples of their blood. Based on measurements of cholesterol, triglycerides, high-density lipoprotein, low-density lipoprotein, and other factors, the researchers conclude that green tea may protect against cardiovascular disease, as well as liver disorders.

University of Kansas researchers reported in 1997 that, by their measurements, green tea is 100 times more effective than vitamin C and 25 times better than vitamin E at protecting cells from damage linked to cancer, heart disease, and other illnesses. They also found the EGCG is twice as powerful as resveratrol, another powerful antioxidant, which is found in red wine, grapes, and other foods.

Researchers in London reported last year that both black and green tea killed a wide range of bacteria, including the antibiotic-resistant and potentially deadly Staphylococcus aureus, “at well below ‘cup of tea’ concentrations,” the researchers wrote. They attributed this to green tea’s catechins and other compounds also found in black tea.

The volatile constituents of green tea were also shown to possess antimicrobial activity, including defense against a bacteria (Bacterium acne) that can lead to acne.

Despite the promising research on green tea, researchers at the University of Texas Center for Alternative Medicine ­Research advise caution before identifying green tea as the ultimate protector against serious disease. For example, they note that the effect of tea consumption on cancer is likely to depend on the causes of the specific cancer—in other words, it may work in some, but not all, instances.

“A lot of the examples we draw upon about green tea had to do with epidemiological studies—people just drinking tea over many years,” Russell says. “It may be that the positive results are showing us that green tea works to prevent cancer, but when you’ve got a full-blown case of cancer, it’s a different story.”

But based on her evaluations of the research, Russell drinks one cup of green tea a day—to keep disease away.

Jan Knight is editor of Herbs for Health. Kenneth Jones of British Columbia, and Cindy L. A. Jones, Ph.D., of Colorado, both frequent contributors to Herbs for Health, provided research support for this article.

This article was taken from THE HERB COMPANION. Read the original article