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People have been drinking tea for thousands of years, but in the last couple of decades a number of potential health benefits have been attributed to this ancient beverage. Black tea and green tea are made from the same plant, but a higher level of the original substances endure in the less-processed green form.
Green tea contains high levels of substances called catechin polyphenols, known to possess strong antioxidant, anticarcinogenic, antitumorigenic, and even antibiotic properties. 1 Based on these findings, as well as observational studies, 2 3 4 5 6 green tea has become popular as a daily drink for preventing cancer and heart disease . However, some observational trials failed to find indications of benefit with green tea. 7 Furthermore, only double-blind, placebo-controlled studies can prove a treatment effective, and there is little direct evidence of this type regarding green tea and cancer or heart disease prevention. 8 (For more information on why double-blind studies are so important, see Why Does this Database Rely on Double-blind Studies? ) One such study...
As a widely consumed beverage, green tea is generally regarded as safe. It does contain caffeine, at perhaps a slightly lower level than black tea, and can therefore cause insomnia, nervousness, and the other well-known symptoms of excess caffeine intake.
Green tea extracts, however, may not be safe. There are a growing number of case reports in which use of a concentrated green tea extract was associated with liver inflammation. 9 In most cases, liver problems disappeared after the extract was discontinued. But, in two cases, permanent liver failure ensued requiring liver transplantation. 10 While it is not absolutely certain that the green tea extract causedthe liver problems, nor how it might do so, these reports do raise significant concerns about use of...