AN INTRODUCTION
-- John H. Weisburger, Senior Member, American Health Foundation

The beverage tea, from the top leaves of the plant Camellia Sinesis, is one of the most widely used beverages, second only to water, in the world. Green tea, oolong tea and black tea are produced as a function of the manufacturing process at the time of harvest of tea leaves. All three types of tea contain antioxidant polyphenols. Tea intake can induce certain phase I cyctochrome P450 enzymes, and phase 2 enzymes such as glucuronyl transferase. The chemopreventive effects of tea depend on its action as an antioxidant, its molecular regulatory functions on cellular growth and development and also on apoptosis, the selective induction of detoxifying enzymes, and a selective improvement in the function of the intestinal bacterial flora. Worldwide epidemiological data, confirmed by detailed laboratory research on the underlying mechanisms, have shown that the oxidation of LDL cholesterol, associated with a risk for atherosclerosis, is inhibited by tea, with a resulting lower risk of coronary heart disease. Many types of cancer are caused by lifestyle elements. One of these is cigarette and tobacco use, leading to cancer in the oral cavity, oesophagus and lung. These are inhibited by green, oolong and black tea. Gastric cancer, caused by a combination of H-pylori and salted foods, is lower in tea drinkers. More research is needed on the inhibition on the Western type of nutritionally linked cancers, specifically cancer of the breast, colon, prostate, pancreas, ovary and endometrium. The formation and actions of key types of carcinogens in human foods, the heterocyclic amines, produced during the cooking of meats, was decreased by green or black tea. Carcinogenesis also involves the formation of reactive oxygen species and radicals, and these effects are inhibited effectively by tea polyphenols. The developmental aspects and growth of these cancers through promotion have also been inhibited by tea. With few exceptions, black and green tea have similar actions, but in a few instances, one or the other type has displayed higher efficacy. The active components of tea are chemicals with multiple beneficial effects, the tea polyphenols, mainly epigallocatechin gallate in green tea, and the tea leaf polyphenol oxidase mediated conversion to oolong and black tea. This oxidation produces other polyphenols such as theaflavin and more complex theraubigins, typical of black tea. All this components have similar antioxidant attributes, and exert similar beneficial biochemical and physiological effects, reflecting the similarities between green and black tea. There is caffeine in the tea leaf, and therefore, in tea. It amounts to about 50 mg caffeine for 125-150 ml cup of tea, one third that in a cup of coffee. Caffeine and the tea polyphenols together contribute to the beneficial acting of tea. There are commercial pills or capsules with the tea polyphenols that display similar activities to those in tea. Also, findings in humans through studies in epidemiology have been confirmed and extended through research in rats or mice, or through in vitro approaches. Thus, the regular use of a widely available, inexpensive beverage, tea, has displayed valuable preventive properties in important chronic diseases affecting humans.

Back 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Next