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TORONTO, CANADA. Tea as a beverage was introduced in 2737 BC by
the Chinese emperor Shen Nung. It has since become one of the
world's most popular beverages with production in 1996 exceeding
2.6 million metric tons. Tea is brewed from the leaves of the
bush Camellia sinensis. There are three different ways of
treating the tea leaves before they are sold. Green tea is made
by drying and steaming the fresh leaves as soon as they are
plucked. Oolong tea is subjected to partial oxidation before
drying and steaming, and black tea undergoes a full oxidation
stage before drying and steaming. Black tea is the most popular
of the three teas and accounts for 76 per cent of the market with
green tea being next at 22 per cent. Recent research has shown
that not only green tea but also black and oolong teas provide
important health benefits. Drs. Siro Trevisanato and Young-In Kim of the University of Toronto have just published a fascinating report detailing the history, biochemistry, and health benefits of tea. It is the richest source of flavonoid antioxidants in the northern European diet and contributes about 63 per cent of all flavonoids in the diet. Tea drinkers have been found to have substantially lower risks of stroke (73 per cent lower) and heart attack (44 per cent lower) than non-tea drinkers. Tea has also been found to lower cholesterol and blood pressure. A Norwegian study found that men who drink one or more cups of tea every day have a 40 per cent lower risk of dying from coronary heart disease than do men who drink less than one cup per day. An American study of 35,000 women found that women who drank two or more cups of tea a day had a 60 per cent lower incidence of cancers involving the digestive tract (mouth, esophagus, stomach, pancreas, colon and rectum) and a 32 per cent lower incidence of urinary tract cancers than did women who did not drink tea. A Canadian study found that men who drink two or more cups of tea a day reduce their risk of prostate cancer by 70 per cent compared to non-tea drinkers.
Tea is safe; it contains only 25 to 34 mg of caffeine so one would
need to drink 10-12 cups a day to approach the caffeine limit
given in the Canada Food Guide. It inhibits the absorption of
non-heme iron, but only if drunk with meals. Therefore
vegetarians who get their iron from non-heme sources should
refrain from drinking tea with their meals or should drink it with
milk or lemon juice added. Tea leaves contain a relatively high
level of aluminum and concern has arisen that a high consumption
of tea may increase the risk of developing Alzheimer's disease.
Fortunately, the aluminum in the leaves is not very soluble in hot
water and there is no scientific evidence that heavy tea drinkers
have higher blood levels of aluminum than do non-tea drinkers.
The Canadian researchers conclude that teas has many health
benefits, is pleasant to drink, and is entirely safe. [72
references]
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