Reading the claims made on the hundreds of Web sites dedicated to green tea, one would think it is a magical elixir of life. Considering its long history, there is little wonder that today people the world over see it as a cure for many ills.
Through the centuries, claims have been made that tea, especially green tea, prevents cancer, restricts increases in blood cholesterol, cures rheumatoid arthritis, deters food poisoning, prevents dental cavities, reduces the risk of circulatory disease and enhances health in a host of other ways.
While green tea has been the subject of literally hundreds of scientific studies over many years, the jury is still out. Some studies find clear health benefits, while others shoot down those same alleged benefits.
Medline, our National Library of Medicine's collection of medical journal articles from around the world, lists 824 articles about green tea. Particular interest has been paid to its potential value to reduce digestive tract problems.
There have been several major studies of green tea's ability to reduce the risk of stomach or gastric cancer. From 1984 through 1992, more than 26,000 men and women in Japan participated in a study on this topic. This carefully designed study, published this year in the New England Journal of Medicine, showed no association between green tea consumption and the risk of gastric cancer.
But another recent well-done but smaller study in China showed the opposite. The investigation, published in the International Journal of Cancer, found green tea protected against stomach cancer and gastritis.
These two studies tell us not only about green tea, but also about medical research: Several excellent investigations are required before final assumptions can be made.
Some animal studies of green tea extracts suggest that they may prevent several types of tumors, but no definitive benefit has yet emerged in studies involving humans. If green tea turns out to be good for our health, in all probability it will be due to its high levels of antioxidants, phytochemicals (plant chemicals) found in many vegetables. Antioxidants are thought to eliminate free radicals--the molecules in the body that can trigger some cancers and other diseases.
Many epidemiological studies suggest that green tea has the additional potential to reduce the risk of skin cancer, coronary artery disease and some microbe-caused infections.
There are yet more claims for green tea. An American Medical Assn. report indicated that green tea can help lower cholesterol and cut the risk of stroke in men. Another report said it may help control constipation, eliminate bad breath and help suppress and reverse aging.
In 1999, researchers at the University of Geneva in Switzerland reported that green tea extract may aid in weight loss because it causes an increase in daily energy expenditure; that is, it helped burn calories faster.
Tea is grown in many parts of the world, from Asia to Argentina. While its leaves vary in size, all teas come from the same plant: the Camellia sinensis. What sets green tea apart from black and oolong teas? Only a variation in processing. Instead of starting with a drying process, green tea is made by steaming fresh leaves at high temperature immediately after plucking. This process prevents fermentation and is believed to inactivate potentially harmful enzymes while leaving healthy antioxidants intact.
These antioxidants, called polyphenols, are found in many fruits, vegetables and grains, as well as in tea. They contain phytoestrogens, which act like the female hormone. It is these chemical components that may account for the claimed medical benefits of green tea.
Only about 20% of all teas marketed around the world are green tea. It is a particularly popular beverage in Asia. In the United States, only about 4% of tea consumed is green. Perhaps surprisingly, about 80% of tea consumed in the United States is iced tea, which was "invented" in 1904 at the Louisiana State Purchase Exposition in St. Louis when the teahouse there could not sell its hot beverages as temperatures soared to 100 degrees.
So, what to do? Drink green tea for one's health? Or simply because it can be refreshing? But drinking any tea too hot can be harmful. If it's so hot it burns or hurts going down, it could increase the risk of esophageal cancer, according to the Food and Drug Administration.
Perhaps green tea will provide some medical benefit; perhaps not. Regardless, it can be a stimulating, pleasant and harmless beverage, with less caffeine than coffee. My advice? Drink and enjoy. If there are ultimately proven health benefits, all the better.
Barrie Cassileth, PhD, is chief of integrative medicine at Memorial Sloan-Kettering Cancer Center in New York She can be reached at firstname.lastname@example.org. Her column appears the first Monday of the month.