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Wageningen Centre for Food Sciences and the Division of Human Nutrition and Epidemiology Wageningen University Bomenweg 2 6703 HD Wageningen Netherlands E-mail: wcfs1{at}staff.nutepi.wau.nl
This book deals with the health effects of green tea, or rather of the polyphenols in tea. Tea is made from the tea plant Camellia sinensis, and tea leaves contain large amounts of polyphenols, most of which are flavonoids of the catechin family. These polyphenols polymerize after the leaves have been harvested, which produces the black tea familiar in the West. However, if the leaves are briefly heated right after harvesting, the polyphenol oxidase enzyme is inactivated, no polymers are formed, and the tea leaves stay green. This is the type of tea favored in China and Japan.
According to the author, the polyphenols from green tea have antibacterial, anticariogenic, and antiviral actions; prevent cancer; lower lipid and glucose concentrations and blood pressure; and reduce fecal odors. These claims are largely based on Hara’s own research, much of which is presented in this book. The author evidently considers green tea to be a panacea: in the preface he states that tea polyphenols "work miraculously in maintaining good health," and that from an early age he was "firmly determined [to] do every possible experiment in order to prove the theory that catechins are responsible for the health benefits of tea."
Such enthusiasm is not necessarily a bad thing. However, every genuine test of a theory is an attempt to refute it, and such critical attempts are lacking from this book. For instance, the incubation of Staphylococcus aureus in catechin at concentrations found in green tea was shown to kill the staphylococci; however, this proves little about the effects of tea drinking on infections in humans: if the polyphenol concentrations found in tea were induced in blood, they would probably kill the patient before they killed the bacteria. Much of the other evidence in the book has similar weaknesses. The promotion of commercial catechin-containing products, complete with pictures, is also out of place in a monograph on food science and technology. The advertised products include capsules, drinks, air purifiers, pet foods, a slug and snail spray, and catechin candies that are purported to have an antiflu effect, about which we are told the following: "Regulations do not allow claims concerning the efficacy, but this knowledge may be spread widely by word of mouth."
This is an entertaining book that contains interesting information on tea and tea polyphenols, but the potential health benefits of green tea and its constituents deserve a more critical analysis.