Interest brewing

The jury's still out on the benefits of green tea, but one thing's clear: Its popularity is picking up


Tea, to China's 18th-century Emperor Chien Lung, was more than a whistle-wetting pick-me-up: It was "that precious drink which drives away the five causes of sorrow."

Western businesses are banking on our buying into Chien Lung's sentiments. In addition to selling a cornucopia of loose green teas, they have distilled the brew's essence and added it to health bars, supplements, diet aids, gum, soft drinks and skin creams - even, in Asia, to Kit Kat candy bars.

Green tea is good for us: That mantra has been chanted in the West since the early 1990s, when studies reported that the infusion, sipped for centuries in China and Japan, appeared to help fight off cancers when drunk by lab mice or rubbed on their skin. Enthusiasm intensified after other studies revealed that green tea contained certain chemicals with cancer-fighting power. Scientists rolled up their sleeves to figure out how it works.

Today, green tea imports are soaring.

"Ten years ago, 3 percent of imported tea was green tea. Now it's 12 percent," says Joe Simrany, president of the Tea Association of the U.S.A.

So confident was one doctor-turned-green-tea businessman that, in 2004, he decided to petition the Food and Drug Administration to permit green teas to sport cancer-fighting health claims on their packages.

The FDA's response was tepid at best.

In June, the agency ruled that there was "no credible evidence" green tea fights cancers of the stomach, lung, colon, esophagus, pancreas or ovary. The agency acknowledged that the evidence for tea fighting breast or prostate cancer was somewhat better, although it also said the link was "highly unlikely" because the evidence on humans wasn't conclusive enough.

Scientists say that despite the unanswered questions, green tea still shows promise, not only as a potential protector against cancer but also against other health threats, such as cardiovascular disease and possibly Alzheimer's. But they also are mindful that many a cell in a dish has been vanquished and many a mouse cured of cancer from therapies that don't pan out in humans.

Producing tea

Green tea is made from the dried leaves of Camellia sinensis, an evergreen shrub native to Asia. The plant is harvested and treated in different ways to produce green tea or black tea.

Green tea is made by steaming the crushed leaves shortly after harvest, destroying enzymes so that chemicals aren't oxidized very much. Leaves used for black tea ferment for days before they're heated, causing the leaves to blacken and creating many chemical changes within them.

Those processing differences may be medicinally important. Both types of tea are abundant in certain antioxidant chemicals called flavonoids, which obstruct the action of cell-damaging free radicals.

Green tea, because it doesn't ferment, has much higher levels of a group of flavonoids called catechins. A potent catechin, epigallocatechin gallate, or EGCG, is three to four times more abundant in green tea than in black.

Scientists note three lines of green tea anti-cancer evidence.

First, there are test-tube studies. Green tea's flavonoids interfere with cancer-related biochemical reactions: They may cause cancer cells to grow sluggishly, cease dividing or even self-destruct. Flavonoids also impede formation of carcinogens known as heterocyclic amines.

Then there are studies in rodents. In one fairly typical study, mice were injected with a tobacco carcinogen that caused them to develop lung tumors. Some of the mice drank green tea, and others did not. The tea-drinking mice got fewer tumors.

Similar studies have linked green tea to protecting against a range of cancers - such as those of the lung, skin, esophagus, colon, bladder and possibly the mammary glands.

EGCG isn't the only thing having an effect. Caffeine is probably providing the lion's share of protection in the case of the skin cancer experiments, and plays a big part in the lung ones, says green tea researcher Chung S. Yang, who heads the chemical biology department at Rutgers University in New Jersey.

The third line of evidence is the one people care most about: What happens to humans when they drink tea? Such studies, because they're usually not done in controlled groups, are tricky to interpret, partly because it's hard to measure how much tea people drink, and partly because tea-drinkers do a lot of other things. For example, it's common in China that men who drink a lot of tea also smoke, Yang says.

The few human studies that have been done have produced mixed results. But despite the complexities, some studies do look good, scientists say.

For example, in an article published in the International Journal of Cancer in 2003, scientists looked at the eating and drinking habits of more than 1,000 Chinese-, Japanese- and Filipino-American women in Los Angeles.

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