Tea-the most popular drink in the world after water-has become increasingly popular in America during the last decade. While tea has been associated with numerous health benefits for some 5,000 years, the last 30 years have brought countless scientific studies that have really begun to explore these benefits.

All tea comes from the same plant, Camellia sinensus, a small warm-weather evergreen shrub with tiny white flowers native to Asia. Depending on where the tea is grown, when it is harvested, which part of the leaf is used and how the leaves are processed, there can be thousands of variations. Black, green and oolong teas comprise the three major classes of tea, while white tea is quickly growing in popularity. (Herbal teas, which do not come from C. sinensis, are associated with their own set of individual health benefits, but are not linked with the research on the potential health benefits of traditional teas.)

To achieve a variety of taste profiles, manufacturers carefully control whether, and for how long, tea leaves are exposed to air, or oxidized. While green and white tea are steamed, dried and rolled without being oxidized at all, black tea is allowed to oxidize for two to four hours. Oolong tea falls somewhere in between, in that the leaves are only partially oxidized.

Like many fruits and vegetables, tea is rich in health-promoting ingredients that studies suggest may contribute substantially to the promotion of health and the prevention of chronic disease. While all tea is healthy to drink, green and white tea contains the highest level of polyphenols, known for their antioxidant activity. These antioxidants are believed to increase longevity by boosting the immune system, regulating cholesterol levels and alleviating the inflammation associated with arthritis. They have also been shown to decrease the risk of certain cancers, including that of the bladder, stomach, liver and breast.

While black tea, the variety favored by most tea drinkers in the United States, may not provide as much antioxidant activity, it has also been proven to prevent blood clots and lower the risk of heart disease by reducing total and LDL cholesterol. Recent studies have also shown that all tea is rich in germ fighting chemicals called alkylamines, which appear to help "prime" your immune system and enable you to fight off bacterial infections. Further, a study done in China last year showed increased bone density in long time tea drinkers.

Here are a couple of important practical tips. While most studies have shown benefits associated with tea come from drinking three to five cups a day, experts have also suggested that this amount of tea is not necessarily required. For decaf drinkers, be aware that up to 70 percent of the antioxidants can be removed in the decaffeination process, depending on which process in used. The process that removes the most antioxidants is ethyl acetate, while the least are removed with a more natural process called effervescense, which retains 95 percent of the polyphenols. Be sure to check labels or contact the manufacturer to see which process was used.

Take advantage of all of the benefits tea has to offer by shopping at the Coop, which offers a wide variety of the teas mentioned above, including fair trade and organic selections. Brands include Choice, Long-life, Eden and Celestial Seasonings.

Dr. Andrew Weil Q&A. Online at www.drweil.com.

Kathleen Doheny. 2003. "Tea for Immunity: Study finds beverage contains a key infection fighter" (April 21). Online at www.healthday.com.

Kim Severson. 2002. "Tea, Totally: Discovering a refuge in an ancient art." San Francisco Chronicle Magazine (March 17): 48.

Maria Rabat. 2002. "News Bites: Big red." Vegetarian Times (January).