What is green tea?
Derived from Camellia sinensis, the same plant that black tea comes from, green tea is, after water, the second most widely consumed beverage in the world. Legend has it that green tea’s aroma and flavor first came to be appreciated over forty-five hundred years ago, when a single leaf chanced to fall into a thirsty Chinese emperor’s cup of hot water. Within a few centuries, the use of green tea had spread to the rest of Asia.
What is green tea used for?
It is interesting to note that although Japan has the highest rate of smoking in the industrialized world, that country also has the lowest rate of lung cancer. That particular datum has troubled scientists to no end, and some have concluded that that nation’s heavy consumption of green tea may be the reason why.
Green tea contains a class of antioxidant beneficial substances called polyphenols, found in many fruits and vegetables. Scientists refer to the polyphenols in green tea as catechins, and suspect that they may be especially healthful, particularly when it comes to the prevention of cancer, often spoken of as “chemoprevention.”
Researchers at Case Western Reserve University demonstrated an especially striking example of chemoprevention with they first dosed a number of rats with green tea, shaved off their fur, and then exposed the now-hairless rats to high levels of ultraviolet radiation. Rats that did not get the green tea were twice as likely to develop skin malignancies as the rats that did, results that led the scientists to conclude that the green tea was preventing cancerous changes in the test animals’ skin cells.
Another study involved human subject at high risk for oral cancers, since they had pre-malignant lesions. Sixty percent of those given green tea extract three times a day for three months saw positive response in the lesions—that is, reduced size, improved appearance, and so on, with those getting the most green tea seeing the greatest improvement. The people who got a placebo experienced no benefit.
Other work in this area has led a number of scientists to believe that green tea also reduces the risk of other cancers, including those of the liver, pancreas, and prostate.
Japanese men also seem to have rather fewer heart attacks than do American men. Work with green tea indicates that this catechin-rich herb may prevent cardiovascular disease by lowering blood pressure, preventing oxidation of LDL (or “bad”) cholesterol, quenching inflammation, and improving insulin sensitivity.
Diabetics and the obese may possibly benefit some day from recent work done with green tea extract. In one US Department of Agriculture study people given green tea and then ingested fifty grams of starch, an amount that would normally provoke a steep rise in blood glucose. Instead, the green tea blocked the digestive enzymes responsible for breaking down starch, and blood sugar went up comparatively little.
Also suggestive is the apparent effect on metabolism of taking several hundred milligrams per day of a particular catechin, EGCG. Scientists have observed an increase in calorie burning, an effect that has lasted up to twenty-four hours, and conclude from this that green tea is a notably thermogenic substance. This and the effect on blood sugar might explain the epidemiological observation that all else being equal, Japanese who are heavy consumers of green tea typically weigh several pounds less than Japanese who are not.
How is green tea taken?
One way to derive whatever benefits are to be had from green tea is simply to do that the Asians do, and drink it. But epidemiological work leads some scientists to conclude that positive effects on health begin only at five to six cups per day, an amount many Americans simply will not consume.
Many people, Westerners especially, will doubtless find it much more convenient to take green tea in the form of a standardized extract in capsule form. Several hundred milligrams ingested one to three times per day ought to be an adequate amount.
Is green tea safe?
Keep in mind that green tea possesses a small amount of caffeine, perhaps a third of that found in a typical cup of coffee. Some people who are especially sensitive to caffeine might wish to avoid it.
Otherwise, green tea has a superb safety record, having been consumed by a quarter of the earth’s population for thousands of years.
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