Tea is a health-promoting beverage in lowering the risk of premature killing chronic diseases: a review.

Abstract

Green and black tea are widely used beverages, second only to water. Tea is an extract of the leaf of the plant Camellia sinensis . The major health benefit of tea is that the leaf contains several polyphenols such as epigallocatechin gallate, and in addition an enzyme, polyphenol oxidase. If upon harvest the leaves are heated, these enzymes are deactivated, and thus, after drying and grinding, the result is green tea. If the leaves are ground and incubated in air at about 40 degree C the polyphenol oxidase converts the original polyphenol to a number of other products such as theaflavin and thearubigins. Upon drying, these are the polyphenols typical of black tea. In most instances, the polyphenols from green tea and black tea have similar properties in health promotion. Coronary heart disease stems from the oxidation by reactive oxygen species of LDL-cholesterol. The tea polyphenols inhibit this reaction. There are data in humans that tea drinkers have a lower risk of heart disease. In animal models, similar findings were made. In the field of cancer causation, we distinguish between genotoxic carcinogens effecting DNA and genes, and other steps associated with the development of cancer, in part also involving reactive oxygen species. Tea and tea polyphenols induce enzymes such as glucuronosyl transferase that detoxify carcinogens. Thus, tea drinkers have a lower risk of cancer and the mechanisms of these reactions have been explored in animal models and through in vitro approaches. Of importance also is that tea decreases the growth of neoplastic cells, but not of normal cells. Tea also enhances apoptosis, a phenomenon of elimination of cancer cells. Tea drinkers also have a healthier intestinal flora, through the inhibition of bacteria that have adverse effects and promotion of the growth of beneficial bacteria. Through the elimination of reactive oxygen species, associated with premature aging, tea drinkers display good health to an old age.