Caffeine

Green teas have about a third the caffeine content, by liquid volume, of coffee. Green teas contain two caffeine metabolites (caffeine-like substances): theophylline, which is stronger than caffeine, and theobromine, which is slightly weaker than caffeine.

Potential effects of green tea on health

Green tea consumption is reportedly associated with various health-promoting properties. For example, it has been shown to promote fat oxidation in humans at rest and to prevent obesity and improve insulin sensitivity in mice.

In a recent study performed at Birmingham (UK) University by Michelle C Venables, Carl J Hulston, Hannah R Cox and Asker E Jeukendrup, it was shown that average fat oxidation rates were 17% higher after ingestion of Green Tea Extract than after ingestion of a placebo. Similarly the contribution of fat oxidation to total energy expenditure was also significantly higher by a similar percentage following ingestion of Green Tea Extract. This proves that ingestion of Green Tea Extract can not only increase fat oxidation during moderately intensive exercise but also improve insulin sensitivity and glucose tolerance in healthy young men.

History

Tea consumption had its origin in China almost 5,000 years ago. Green tea has been used as traditional medicine in areas such as China, Japan, India and Thailand to help everything from controlling bleeding and helping heal wounds to regulating body temperature, blood sugar and promoting digestion.

The Kissa Yojoki (Book of Tea), written by Zen priest Eisai in 1191, describes how drinking green tea can have a positive effect on the five vital organs, especially the heart. The book discusses tea's medicinal qualities, which include easing the effects of alcohol, acting as a stimulant, curing blotchiness, quenching thirst, eliminating indigestion, curing beriberi disease, preventing fatigue, and improving urinary and brain function. Part One also explains the shapes of tea plants, tea flowers, and tea leaves, and covers how to grow tea plants and process tea leaves. In Part Two, the book discusses the specific dosage and method required for individual physical ailments.

source: http://en.wikipedia.org/wiki/Green_tea

A Cup of Tea

Green tea leaves steeping in an uncovered gaiwan

For many years, green tea has been associated with positive health benefits. In a recent study by researchers at Purdue University, the nature of these benefits was codified. The researchers found that epigallocatechin gallate (EGCg), a compound found in the tea, inhibited the growth of cancer cells. The compound also killed cancer cells without causing harm to healthy tissue. This is one of the first studies to provide a direct link between epigallocatechin gallate and cancer inhibition.

Green tea leaves are potent in EGCg. The study suggests that consumption of four to five cups of green tea may slow cancer. Previous studies have found a lower incidence of cancer in those who consume this amount of green tea but the exact compound that produced this cancer inhibition was unknown.

All tea comes from the same botanical source. Unlike other types of tea, green tea is processed differently. In green tea, the leaves are not allowed to oxidize but instead are steamed. This process allows the natural ingredients in the leaves to be preserved. Other types of tea were not nearly as successful as green tea in inhibiting the cancerous cells. Green tea was approximately ten times more potent than the other types.

Quinol oxidase or NOX is the enzyme that is inhibited by EGCg. NOX is present in cancer cells and is required for growth in cancer cells as well as normal cells. Under normal conditions, cells only express NOX due to hormonal stimulation. Cancerous cells, however, express NOX all of the time. The researchers found that, at certain levels, EGCg inhibited NOX on cancerous cells and not on normal cells. By limiting the growth and development of the cancerous cells, the cells did not grow to the required minimum size to divide and cell apoptosis occurred.

The scientists want to expand on these studies and determine the exact mechanism of NOX inhibition. At this point, the scientists are beginning to understand the initial inhibitive effects of EGCg but further research is warranted to pin down the exact mechanisms.

What do you think? Might other types of compounds display similar benefits? How much of a role does diet and exercise play in stopping cancer as opposed to genetic predisposition? Come on over to the Biology Forum and share your thoughts, opinions, and feelings. 'Til next time...

Green Tea for Breast Cancer

Green tea has many health benefits, some have been proven and some may just be folklore. One particular effect that green tea seems to have is to fight and/or prevent breast cancer.

I would like to provide some information on this, but please remember that I'm just a lowly tea drinker and not a doctor or a chemical engineer. Much of the research is just plain over my head, so I will just summarize to the best of my abilities.

First of all, what is green tea? Just like black tea, it comes from the Camellia sinensis plant. Black tea is fermented and green tea is not (oolong tea is partly fermented). Green tea is very popular in China and Japan and is gaining favour in other nations too. They have been drinking green tea for health reasons for over 5,000 years in Asia.

Some of the various chemical compounds in green tea:

• polyphenols and flavonoids
• alkaloids, such as caffeine and theobromine
• carbohydrates
• tannins
• minerals, such as fluoride and aluminum

When it comes to cancer treatment and prevention, it's the polyphenols that are important. Green tea has higher amounts of these chemicals than black tea because the fermentation process alters their composition. Of all the different polyphenols, one seems to stand out above the rest. EGCG (epigallocatechin gallate) is a very powerful antioxidant and is believed to be an important player in the therapeutic qualities of green tea. How it works is still unclear, but it may inhibit cell-replication enzymes (preventing cancer growth) as well as other cellular processes that are too complicated to get into.

In various studies, rats with breast tumors were given green tea to drink and compared to similar rats that only drank water. The green-tea-rats had reductions in tumor size, and new tumors were slower to develop. There don't seem to have been any studies on humans yet.

For humans to gain any health benefits, you would need to drink around 3-4 cups every day (without milk or sugar). For people who are at-risk for developing cancer, it might be a worthwhile avenue to pursue. I think for the everyday person, that's a lot of tea to drink. You can also get your green tea in capsule form, but there have been no studies done on the effectiveness of such pills.

A major concern with drinking so much tea is the caffeine. Though there is less caffeine in tea than in coffee, it does start to add up when drinking large volumes. But can you switch to decaf? The answer is, maybe. It all depends on how your chosen tea is decaffeinated. Tea that has been decaffeinated with a solvent (such as Ethyl Acetate) is going to have a much lower level of EGCG, than a tea that has been processed with a water/carbon dioxide method. Water decaffeinated tea will retain almost 95% of its EGCG.

So there is one more good reason for us women to drink green tea. I read that green tea might also help against prostate cancer, but that's another article altogether.

Source: http://coffeetea.about.com

The Miracle of Green Tea

Is any other food or drink reported to have as many health benefits as green tea? The Chinese have known about the medicinal benefits of green tea since ancient times, using it to treat everything from headaches to depression. In her book Green Tea: The Natural Secret for a Healthier Life, Nadine Taylor states that green tea has been used as a medicine in China for at least 4,000 years.

Today, scientific research in both Asia and the west is providing hard evidence for the health benefits long associated with drinking green tea. For example, in 1994 the Journal of the National Cancer Institute published the results of an epidemiological study indicating that drinking green tea reduced the risk of esophageal cancer in Chinese men and women by nearly sixty percent. University of Purdue researchers recently concluded that a compound in green tea inhibits the growth of cancer cells. There is also research indicating that drinking green tea lowers total cholesterol levels, as well as improving the ratio of good (HDL) cholesterol to bad (LDL) cholesterol.

To sum up, here are just a few medical conditions in which drinking green tea is reputed to be helpful:

• cancer
• rheumatoid arthritis
• high cholesterol levels
• cariovascular disease
• infection

• impaired immune function

What makes green tea so special?

The secret of green tea lies in the fact it is rich in catechin polyphenols, particularly epigallocatechin gallate (EGCG). EGCG is a powerful anti-oxidant: besides inhibiting the growth of cancer cells, it kills cancer cells without harming healthy tissue. It has also been effective in lowering LDL cholesterol levels, and inhibiting the abnormal formation of blood clots. The latter takes on added importance when you consider that thrombosis (the formation of abnormal blood clots) is the leading cause of heart attacks and stroke.

Links are being made between the effects of drinking green tea and the "French Paradox." For years, researchers were puzzled by the fact that, despite consuming a diet rich in fat, the French have a lower incidence of heart disease than Americans. The answer was found to lie in red wine, which contains resveratrol, a polyphenol that limits the negative effects of smoking and a fatty diet. In a 1997 study, researchers from the University of Kansas determined that EGCG is twice as powerful as resveratrol, which may explain why the rate of heart disease among Japanese men is quite low, even though approximately seventy-five percent are smokers.

Why don't other Chinese teas have similar health-giving properties? Green, oolong, and black teas all come from the leaves of the Camellia sinensis plant. What sets green tea apart is the way it is processed. Green tea leaves are steamed, which prevents the EGCG compound from being oxidized. By contrast, black and oolong tea leaves are made from fermented leaves, which results in the EGCG being converted into other compounds that are not nearly as effective in preventing and fighting various diseases.

Other Benefits

New evidence is emerging that green tea can even help dieters. In November, 1999, the American Journal of Clinical Nutrition published the results of a study at the University of Geneva in Switzerland. Researchers found that men who were given a combination of caffeine and green tea extract burned more calories than those given only caffeine or a placebo.

Green tea can even help prevent tooth decay! Just as its bacteria-destroying abilities can help prevent food poisoning, it can also kill the bacteria that causes dental plaque. Meanwhile, skin preparations containing green tea - from deodorants to creams - are starting to appear on the market.

Harmful Effects?

To date, the only negative side effect reported from drinking green tea is insomnia due to the fact that it contains caffeine. However, green tea contains less caffeine than coffee: there are approximately thirty to sixty mg. of caffeine in six - eight ounces of tea, compared to over one-hundred mg. in eight ounces of coffee.

Source: http://chinesefood.about.com/library/weekly/aa011400a.htm