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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