Friday, 18 July 2014

Green Tea, Health Benefits and Aplications (Part I)




What you eat and drink can be the cause of a disabling or deadly disease, or it can extend your life span to a healthy old age. What is beneficial and what is harmful? In the United States, and many other countries, investments have been made in medical research that have led to major successes in disease prevention, diagnosis, and therapy. Advances in the
basic sciences such as nutrition, biochemistry, pharmacology, and pathology have provided an understanding of cell and tissue behavior and factors that impinge on their proper functioning, as well as the elements that go wrong and lead to disease processes.
     Despite these advances, however, there is still significant premature mortality from cardiovascular diseases, many types of cancer, and problems associated with aging, such as
Alzheimer’s disease and other mental and psychiatric conditions. Many of these diseases have been found to be associated with nutritional traditions, eating habits, and life-style. For not all fats have the same adverse effects. Olive oil and canola oil do not increase the risk of the nutritionally linked cancers and of heart disease. There is a lower incidence of heart disease and the nutritionally linked cancers in the Mediterranean region, in particular in Greece and southern Italy, where olive oil is favored. Nevertheless, digestible oils or fats have the same high caloric value of 7 kcal/g, compared to only 4 kcal/g for starches and proteins. This high caloric value needs to be taken into account to avoid obesity, a major problem in North America. Obesity stems from excessive caloric intake over calorie needs for the normal functioning of the body. Populations of industrialized nations tend to be more and more sedentary, with the consequent lower caloric requirement.
      Wholesome drinking water supplies are also important. Most people in the Western world, in Japan, and in most regions of the large subcontinent of China have access to running water that is treated through filtration and chlorination to be safe to drink. Regrettably, in some areas of the world, water is contaminated by bacteria and undesirable chemicals. One solution to avoid bacterial contamination is to boil the water before use. The introduction of the wholesome and tasty beverage of tea thousands of years ago has provided a universal solution to the problem of providing humanity with a safe beverage. However, there are many additional benefits to the intake of tea. First, adults should consume about 2–2.5 liters of fluids a day. About one-third—700–800 ml—might be in the form of hot or cold tea. In the Orient, green tea is favored, but in most of the Western world, black tea is the beverage of choice.

      Tea comes from the top leaves of the plant Camellia sinensis. These leaves contain as principal product a powerful antioxidant, epigallocatechin gallate (EGCg), and minor amounts of other catechins. All these chemicals are polyphenols. The fresh leaves also contain an enzyme, polyphenol oxidase. When the freshly collected leaves are treated with steam or heated in a pan, the polyphenol oxidase is inactivated. Drying of the heated leaves followed by chopping and rolling yields green tea. If upon harvest and chopping to liberate the polyphenol oxidase the leaves are allowed to stand at about 40°C for 30 minutes, there is a partial biochemical oxidation of the polyphenols and the result is oolong tea, favored in southern China and Southeast Asia. Allowing the oxidation to run for 60–90 minutes converts the polyphenols to those typical of black tea, such as theaflavins and thearubigins.
     Detailed research shows that the antioxidant polyphenols from green, oolong, or black tea have similar beneficial effects. For example, they decrease the oxidation of LDL-cholesterol, a risk factor for coronary heart disease. The antioxidants also reduce the oxidation of DNA, consequent to the action of carcinogens and to the peroxidation reactions on lipids, generating oxy radicals and peroxides. In addition, theycan induce enzymes in tissues such as liver that help detoxify harmful chemicals, including carcinogens, and lower the risk of promoting chemicals in the overall cancer process. Tea polyphenols also decrease the rate of cell duplication, especially of abnormal, transformed cells involved in cancer development. This property slows the growth of early cancer cells and may even be beneficial as adjuvant therapy of neoplasia.
There are also some indications that regular intake of tea modifies the intestinal bacterial flora, enhancing the growth of beneficial bacteria and eliminating those with possibly harmful attributes. Clearly, tea is an inexpensive beverage, that is easily made, hot or cold, and pleasant and tasty. It can be consumed neat or with a little milk, sugar, or lemon. It is
sterile regardless of the quality of water used, since boiling is the customary way of preparing it.
     The scientific progress in the field of tea and health has been remarkable in the past 15 years. These advances have been recorded in numerous scientific publications, reviews, and presentations at symposia and conferences. Yet, a single overview of the many aspects of tea production, its inherent properties and constituents, analysis, chemical and biochemical functions, actions in lowering risk of cardiovascular diseases and cancers, and the relevant underlying mechanisms has not been available. We owe a debt to Dr. Yukihiko Hara for providing a detailed treatise on this topic that particularly emphasizes the significant health benefits to be gained by the oral intake of tea catechins. In addition, his discussion of their
practical utility is sure to be of interest not only to those in tea and health sectors but also in other diverse industries where possibilities for utilizing tea catechins exist. Dr. Hara is one
of the world’s experts on the manifold aspects of tea and health, and we are indebted to him for taking the time to enrich us by sharing his vast knowledge.
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