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In 1872, Anglo-Irish writer Joseph Sheridan Le Fanu published "Green Tea," an eerie short story in which a reverend is continually terrorized by a monkey that no one else can see. The reverend's doctor concludes that the arrival of his patient's simian companion resulted from drinking too much green tea.

We've come a long way from believing that green tea causes hallucinations. In the early 21st century, green tea is seen as anything but harmful. In fact, the beverage is routinely touted as having preventative and curative properties. Not surprisingly, these healthful claims are especially widespread on tea company websites. We've all heard that green tea is good for us, but what exactly are its beneficial ingredients? And is there any real evidence that green tea prevents disease or slows its progression?

All varieties of tea - black, green and oolong - derive from the leaves of the Camellia sinensis plant. What distinguishes the three varieties is the degree of fermentation. Black tea is fully fermented, oolong is partially fermented and green is unfermented. Green tea contains the most antioxidants - about 50-150 mg of catechins per cup - of the three tea varieties. Catechins, which are reputedly more potent antioxidants than vitamin C, give green tea its healthful reputation.

Antioxidants such as catechins combat the effects of free radicals, which are compounds that damage cells. Although free radicals are naturally occurring, toxins such as pollution, radiation and the sun's ultraviolet rays also promote the production of these harmful compounds. Free radicals are thought to accelerate the aging process and contribute to the development of illnesses such as cancer and heart disease. Catechins prevent or reduce the damage of free radicals by neutralizing their effects.

Since green tea is one of the richest sources of catechins, you'd expect its benefits to be undisputed. Heart disease and cancer are less prevalent in Asian countries where large quantities of green tea are consumed, but many experts are not convinced that green tea is effective in preventing disease or slowing its progression. Green tea also appears to be more effective for some conditions than others, and some studies of its effects are conflicting.

Population-based studies, in which large groups are followed over many years, implicate green tea consumption in preventing coronary artery disease through anticoagulant and cholesterol-lowering effects. Various studies show

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