緑茶の持つ特別な効能に医学研究者達の注目が集まっています。２０１２年１月２４日にJamaica Gleaner新聞に掲載された記事（下記全文）の中では高級な緑茶（抹茶・玉露）などに多く含まれるテアニンの効能について詳しく書かれています。
Published by Jamaica Gleaner on January 24, 2012
A TEA lover, Bernard-Paul Heroux, once wrote: "There is no trouble so great or grave that cannot be much diminished by a nice cup of tea."
Today, medical research clearly highlights the special health benefits of a specific tea - green tea, a drink made from the leaves of the tea plant (Camellia sinensis)
. The same plant produces green tea,black tea
, and oolong tea, but because of the way it is processed, green tea is truly unique.
Tea is the most consumed beverage in the world besides water and has been used by man for millennia. Much of its benefits have been attributed to potent antioxidants found in the tea leaves called polyphenols. These substances are also found in smaller amounts in other plant foods like cocoa.
Recently, however, researchers have identified another substance that is found only in the tea plant. It is a special amino acid called theanine that accounts for the ability of tea to create relaxation while energising the drinker. Theanine is the predominant amino acid in green tea leaves and gives tea its characteristic taste while contributing to many of its other medicinal benefits.
Theanine combats stress
When someone suggests that you have a cup of tea and relax, they are really asking you to have a cup of theanine. Although green tea contains small quantities of natural caffeine, the calming effect of the theanine in it balances the stimulating effects of caffeine on the nervous system. Researchers have demonstrated that theanine creates this sense of relaxation about half an hour after ingestion by two separate actions:
First, it stimulates the electrical activity of the brain to produce a state of relaxation and mental alertness similar to that achieved through meditation. Second, theanine causes the brain to increase its levels of two neurotransmitters, dopamine and serotonin. These important brain chemicals produce feelings of well-being and relaxation. Theanine is particularly useful for people under stress as it helps to alleviate its negative effects without producing sedation or drowsiness.
Theanine promotes learning
Theanine enhances your ability to learn, remember, and concentrate, a reason why monks and scholars have historically used drinking green tea as an aid to meditation and study. It is particularly useful when you are multitasking as it helps you to focus more effectively.
Researchers found that it even synergises with caffeine to boost the activity of brain cells. They found that 100 milligrams of theanine when consumed with 60 milligrams of caffeine enabled people to focus better on complicated tasks, a combination found in roughly four cups of green tea.
Theanine and cancer
A study published by Sadzuka et al in 2002, found that theanine might help cancer patients by improving the efficacy of cancer drugs, and through its relaxing effects. Theanine increased the concentration of anti-cancer drugs in tumours while lowering the levels of anti-cancer drugs in the healthy tissues where they are not needed. This improved the effectiveness of the therapy while decreasing its side effects. In addition theanine itself also inhibited the growth of cancerous tumours. In Japan, where green tea is very popular, surveys showed that regular green-tea drinkers had a much lower incidence of breast, prostate, liver, pancreatic, lung, oesophageal, and stomach cancers.
Theanine for weight loss
Green tea is well known to help with weight loss, and according to a 2004 Japanese study, theanine contributes to this fat-burning effect. In this research using animals, theanine lowered body weight, body fat, and triglycerides (blood fat) levels. Beside the fact that tea contains zero calories, green tea helps to curb food cravings. The social habit of "afternoon tea" was supposedly started by the 7th Duchess of Bedford in England to quiet her hunger pangs between lunch and dinner.
Theanine for blood pressure and cholesterol
Individuals with high blood pressure can benefit from drinking green tea. Japanese researchers report that theanine lowers high blood pressure, but has no effect on normal blood pressure. Studies have shown that theanine is particularly useful in 'spontaneous hypertension' which is high blood pressure resulting from stress, excitement or shock. The soothing, calming effects of theanine appear to offset this dangerous condition.
Theanine was also found to reduce total cholesterol levels in humans, while preventing good cholesterol from being converted into bad cholesterol by oxidation.
Theanine improves immune function
Studies at Harvard Medical School and Brigham and Women's Hospital demonstrated that theanine increased the body's immunity against colds and flu and promotes a strong immune response to infections. Theanine also aids in preventing abnormal immune system reactions as occur in allergies and autoimmune diseases.
Side effects
Theanine is safe and non-toxic, and drinking green tea is associated with very few side effects. Staining of the teeth is probably the commonest problem, and using a toothpaste containing bicarbonate and hydrogen peroxide can prevent this. By the way, green tea prevents halitosis (bad breath). Researchers at the University of Illinois found that some of the polyphenols in tea inhibit the growth of bacteria in the mouth that can cause this unpleasant odour. Theanine reduces caffeine sensitivity. You can overcome this problem by starting with small amounts of green tea while supplementing with magnesium and the B vitamins.
Benefit fully from green tea
In order to get all the benefits from green tea listed above, the research suggest that one would have to drink several cups of green tea daily. Modern technology has dealt with this problem by creating a patented green tea concentrate in powder form. Half of a teaspoonful of the powder (Herbal Tea Concentrate) makes a cup of tea (hot or cold) that provides the benefits of several cups made from regular green tea leaves. I use this green tea concentrate myself and recommend it to all my patients. It is an ideal healthy breakfast beverage.
More information: http://jamaica-gleaner.com/gleaner/20120124/news/news6.html
