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Tea for 250 million?

The year: 2735 B.C. The place: China. At a reception held by Emperor Shen Nung, leaves from an evergreen shrub accidentally fall into boiling water.

Fast forward almost five thousand years. Researchers discover clues that the resulting beverage--ordinary tea--may prevent cancer.

So far, the evidence that tea can protect against cancer comes almost exclusively from animal studies. But those studies are compelling.

"There's no agent in the literature that has shown such remarkable effects in so many [animal] systems," says Hasan Mukhtar, research director in dermatology at Case Western Reserve University in Cleveland. "This has never happened before."


Not coffee. Not milk. Not Coca-Cola. Nope. The most popular beverage in the world is tea.

"By tradition, people in the Orient prefer green tea or oolong tea," explains John Weisburger, director emeritus of the American Health Foundation in Valhalla, New York. "The rest of the world drinks black tea." It accounts for 80 percent of the world tea crop.

The difference isn't just cosmetic. To make green tea, the leaves are chopped, rolled, and quickly steamed or heated. The quick heating stops an enzyme that inactivates the tea's polyphenols (which are antioxidants).

On the other hand, explains Weisburger, "if the leaves are chopped, rolled before drying, and allowed to react in air for about six hours, the polyphenols are oxidized by the enzyme, and the result is black tea." (Oolong tea is in between green and black tea. It's exposed to air for one or two hours.)

Of course, the ancient Chinese tea-makers didn't know from polyphenols. Yet if tea reduces the risk of cancer and heart disease, polyphenols may explain why.


Care for a spot of epigallocatechin gallate?

Affectionately known as EGCG, it's the major polyphenol in green tea. Black tea has lower levels of other polyphenols, but they aren't as well studied, perhaps because research on tea started in green-tea-drinking Japan.

Green tea's ability to prevent tumors in animals has bowled over most investigators. So far, animals given carcinogens and green tea--or EGCG in water--have developed fewer tumors of the skin, lung, esophagus, forestomach, small intestine, colon, liver, pancreas, and breast.(1)(2)(3)

"Tea is impressive," says Chung S. Yang, an expert on tea and cancer at Rutgers University in New Jersey, "because it inhibits such a broad spectrum of cancers."

Two other factors set tea apart from other possible cancer-preventers. First, it cuts tumor rates when fed at levels that approximate what people drink.

"Some garlic components can inhibit NNK [a tobacco constituent that causes lung cancer] much more than tea," says Yang. "But with those compounds, we use 100 times what people eat. With tea, it's in the upper range of what people eat."

What's more, tea seems to inhibit tumors at different stages. "We can give it early when we give the carcinogen, during the promotional phase when cells are proliferating, or after the tumors appear," says Yang. No matter when the tea is administered, the number of tumors--or their growth--is slashed.

"That's very unusual for a chemopreventive agent. Garlic compounds, for example, only work if you give them with the carcinogen."

What about black tea? "In some animal studies, green and black tea are comparable," says Yang. It depends on the tumor site, the strain of mice or other animal, and whether the tea is given early or late in the cancer process.

"It's the same with decaffeinated tea," he adds. "Sometimes the results are comparable [to ordinary green tea]. Sometimes they're not."


One sip of those animal studies and you'd think that tea were poised to put the National Cancer Institute out of business.

It isn't, and it's all because of a teensy little sticking point: human studies. So far, they haven't consistently found a lower risk of most cancers in tea-drinkers.(1) Some have even found a higher risk.

Most scientists aren't too worried that tea is harmful. In 1991, the International Association for Research on Cancer concluded that there isn't enough evidence to say that tea causes cancer in people. The simplest explanation for the higher rate of cancer in some tea-drinkers: it usually (but not always) shows up in places like Kazakhstan, Iran, and parts of China, where people drink their tea burning hot (130[degrees] to 150[degrees]F).

"Very hot fluids increase the risk of esophageal cancer because the pipe gets injured over the years," says Joseph McLaughlin, formerly of the National Cancer Institute and now president of the International Epidemiology Institute in Rockville, Maryland.

Last June, Yu Tang Gao of the Shanghai Cancer Institute and McLaughlin published a large study comparing the tea-drinking habits of esophageal cancer patients in Shanghai to their healthy counterparts.(4) Women who drank the most green tea were half as likely to have the disease.

In men, tea drinking cut the risk about the same, but only among the small number who didn't smoke or drink alcohol. Smoking and drinking are the biggest contributors to esophageal cancer, says McLaughlin. "Tea may not be able to overcome all that."


There are other clues that tea protects against cancer in people, but they're fragmentary and inconsistent.(1)

For example, "Lung cancer mortality among males in Japan is considerably lower than it is in the United States even though the prevalence of cigarette smoking during the last 40 years among Japanese males is much higher than in the United States," writes Yong Xu of the Chinese Academy of Preventive Medicine in Beijing.(2)

But don't think you can safely wash down that cigarette with a cup of tea. Diet, race, or smoking patterns could also explain the lower Japanese death rate, Yu cautions.

What could explain dynamite animal studies and flimsy human evidence? Lots of things.

"Many of the earlier human studies didn't have the power to adjust for confounders," says Rutgers' Yang.

"If researchers didn't control for smoking or fruit and vegetable consumption, for example, those confounders might have a greater impact on cancer and tea wouldn't have shown up."

It's also possible that tea has a weaker effect in humans than in animals, and that people simply don't drink enough tea for it to matter.

Or, tea may protect against cancer caused by some carcinogens, but not others. "If stomach cancer is caused by nitrosamines in Japan, you may see a protective effect there," speculates Yang. "But the causative factors may be different in the United Kingdom, so you might not see it there."


"Reduces cholesterol, soothes & slims," says the label on Col-S-Rol Slim Tea.

Yet if tea's link to cancer is fuzzy, it's even fuzzier for heart disease.

A polyphenol isolated from tea keeps LDL ("bad") cholesterol from getting oxidized in test tubes.(5) And, in one preliminary report, blood antioxidant levels rose after ten people drank black or green tea.(6)

The most exciting evidence: Last year, Michael Hertog reported on a study of 805 men aged 65 to 84 in the Netherlands. After five years, the risk of dying from a heart attack was 58 percent lower in those who consumed the most flavonoids, a group of polyphenols in tea.(7)

The largest source of flavonoids in the men's diet: 61 percent came from black tea. (Apples and onions contributed most of the remainder.)

Exciting, yes. Strong evidence? Not by a long shot. A handful of studies in people, animals, and test tubes means researchers are just at the starting gate.


What should people make of so much promising but confusing evidence?

Most researchers say that it's far too early to encourage people to drink tea by the potful to prevent disease. Rutgers' Yang, for example, has a cup or two a day, because he likes it, not just because it may be good for him.

"People who enjoy drinking tea may end up healthier," he says. But the research "is still in its infancy."

(1)Journal of the National Cancer Institute 85: 1038, 1993.

(2)Cancer Research 52: 3875, 1992.

(3)Journal of Investigative Dermatology 102: 3, 1994.

(4)Journal of the National Cancer Institute 86: 855, 1994.

(5)Biochemical Pharmacology 43: 445, 1992.

(6)Lancet 344: 626, 1994.

(7)Lancet 342: 1007, 1993.


* Tea--whether green or black, regular or decaffeinated--may reduce the risk of cancer and possibly heart disease, but the evidence in humans is incomplete.

* None of the evidence on tea applies to herbal teas, which are chemically unrelated.

* Don't drink your tea burning hot. High temperatures may increase the risk of cancer by injuring your esophagus.

* Don't use this article as an excuse to guzzle sweetened iced tea like Snapple or Arizona. Sip a 20-oz. bottle at your desk and you'll swallow 15 to 16 teaspoons of sugar. It's as sweet as soda pop.

* If you want to try green tea, look for it in Asian food stores and at Japanese (not most Chinese) restaurants. Lipton, Earl Grey, and almost all other teas are black.
COPYRIGHT 1994 Center for Science in the Public Interest
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1994, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:includes related information
Author:Liebman, Bonnie
Publication:Nutrition Action Healthletter
Date:Nov 1, 1994
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