The Miracle of Green Tea "Better to be deprived of food for three days, than tea for one."(Ancient Chinese Proverb)
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: 1. cancer 2. rheumatoid arthritis 3. high cholesterol levels 4. cardiovascular disease 5. infection 6. 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." 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.
Tea and Cancer Prevention
- The antioxidants found in tea--called catechins--may selectively inhibit the growth of cancer (see question 1).
- In laboratory studies using animals, catechins scavenged oxidants before cell damage occurred, reduced the number and size of tumors, and inhibited the growth of cancer cells (see question 3).
- However, human studies have proven more contradictory, perhaps due to such factors as variances in diet, environments, and populations (see Question 4).
- NCI researchers are investigating the therapeutic and preventive use of tea catechins against a variety of cancers (see Question 5).
Tea drinking is an ancient tradition dating back 5,000 years in China and India. Long regarded in those cultures as an aid to good health, researchers now are studying tea for possible use in the prevention and treatment of a variety of cancers. Investigators are especially interested in the antioxidants-called catechins-found in tea. Despite promising early research in the laboratory, however, studies involving humans so far have been inconclusive.
1. What are antioxidants?
2. What is the level of antioxidants found in tea?
3. What are the laboratory findings?
4. What are the results of human studies?
5. Is NCI evaluating tea?
Other ongoing NCI studies are testing green tea as a preventive agent against skin cancer. For example, one is investigating the protective effects of a pill form of green tea against sun-induced skin damage while another explores the topical application of green tea in shrinking precancerous skin changes. For more information about NCI-sponsored studies on green tea, go to http://www.cancer.gov/clinical_trials/.
ScienceDaily (Aug. 5, 2003) — Green tea's ability to fight cancer is even more potent and varied than scientists suspected, say researchers who have discovered that chemicals in green tea shut down one of the key molecules that tobacco relies upon to cause cancer. It's a find that could help explain why people who drink green tea are less likely to develop cancer. The finding by scientists at the University of Rochester's Environmental Health Science Center appears in the July 21 issue of Chemical Research in Toxicology, published by the American Chemical Society.
Graduate student Christine Palermo and adviser Thomas Gasiewicz, Ph.D., set out to measure the effects of the chemicals found in green tea on a molecule known as the aryl hydrocarbon (AH) receptor, a molecule that frequently plays a role in turning on genes that are oftentimes harmful. Gasiewicz has previously shown how both tobacco smoke and dioxin manipulate the molecule – a favorite target of toxic substances – to cause havoc within the body.
The team isolated the chemicals that make up green tea and found two that inhibit AH activity. The two substances, epigallocatechingallate (EGCG) and epigallocatechin (EGC), are close molecular cousins to other flavonoids found in broccoli, cabbage, grapes and red wine that are known to help prevent cancer.
While green tea has been much-ballyhooed for its anti-cancer effects as well as other purported abilities such as preventing rheumatoid arthritis and lowering cholesterol, just how the substance works has been a mystery. Scientists do know that green tea contains chemicals that are anti-oxidants and quench harmful molecules. But its effects on the AH receptor have not been thoroughly evaluated until now.
"It's likely that the compounds in green tea act through many different pathways," says Gasiewicz, professor and chair of Environmental Medicine and director of Rochester's Environmental Health Science Center. "Green tea may work differently than we thought to exert its anti-cancer activity."
Gasiewicz and Palermo showed that the chemicals shut down the AH receptor in cancerous mouse cells, and early results indicate the same is true in human cells as well. In the laboratory the AH-inhibiting effects of green tea become evident when EGCG and EGC reach levels typical of those found in a cup of green tea. But the scientists say that how green tea is metabolized by the body is crucial to its effectiveness, and that results in the laboratory don't necessarily translate directly to the dinner table.
"Right now we don't know if drinking the amount of green tea that a person normally drinks would make a difference, but the work is giving us insight into how the proteins work," says Palermo, who enjoys cold green tea herself. "There are a lot of differences between various kinds of green tea, so a lot more research is needed."
For this work Palermo received the award for best poster in the chemical carcinogenesis specialty section at the meeting of the Society of Toxicology in March. Now she is studying exactly how green tea inhibits the AH receptor. After she graduates Palermo plans to study links between environmental agents and childhood leukemia.
In addition to Palermo and Gasiewicz, other authors are former post-doctoral associate Jose Martin Hernando and chemist Andrew Kende, who teased apart the components of green tea extract; and Stephen Dertinger, a former student who first had the idea to test green tea's effects on the AH receptor. The work was funded by the National Institute of Environmental Health Sciences and the American Institute for Cancer Research.
In a study published in the open access journal BMC Medicine, researchers show that tea acts at the cellular level, by inhibiting inflammatory pathways, to reduce inflammation. They also show that tea extracts reduce the duration of radiation-induced skin damage by up to 10 days in patients who received radiation treatment.
Frank Pajonk, from the University of California in Los Angeles, USA, and colleagues from the University of Freiburg, Germany, studied the effects of green tea and black tea extracts on patients who had been treated with radiotherapy, which can damage the skin. The authors then analysed the effects of the same tea extracts on human and mouse white blood cells in culture.
Pajonk et al. find that tea extracts reduce the duration of skin toxicity following radiotherapy by 5 to 10 days. Green tea extracts are more effective than black tea extracts in some patients. Pajonk et al. also show that tea extracts reduce the release of pro-inflammatory cytokines, such as IL-1beta, IL-6, IL-8, TNFalpha and PGE2, in human white blood cells in culture, with green tea having higher anti-inflammatory properties than black tea. Both black tea and green tea inhibit one major inflammatory pathway in mouse white blood cells.
Pajonk et al. add that tea's high content of polyphenols is likely to be responsible for its high anti-inflammatory activity, but that other pathways are probably involved in its clinical effectiveness.
Digestive Process Affects Anti-cancer Activity Of Tea In Gastrointestinal Cells ScienceDaily (Apr. 10, 2008) — Increased consumption of teas rich in catechins is associated with reduced risk of stomach, colon and other gastrointestinal cancers. However, the effects of digestion on the anticancer activity of tea catechins have largely been ignored. A study by nutrition researchers at The Ohio State University and Purdue University found that the digestive process could both alter the structure of the tea catechins and their anticancer activity.
Using a model simulating gastric and small-intestinal digestion, the researchers treated gastric cancer cells and colon cancer cell lines with digested and undigested (parent) extracts of green, tea, black tea, and a combination of the most active tea catechins (EGCG/EGC). In colon cells, digestion of both the green tea extracts and the catechin combination significantly reduced anticancer activity compared to undigested parent extracts. Black tea, on the other hand, showed the same anticancer activity for both parent and digested extracts. Digestion and the type of tea made a difference in terms of anticancer activity. In addition, the anticancer activity of the tea extracts differed between gastric and colon cancer cell lines. In gastric cancer cells, the undigested extracts were 50 percent less effective than in colon cancer cells.
What does the new study show us?
Second, say the researchers, some of the digestive changes may impact anti-cancer activities. Work in Dr. Ferruzzi's laboratory has shown that digestion can alter the structure of polyphenols, degrading and destroying some while forming others. His laboratory is currently identifying these new compounds and testing their own anticancer activity.
Third, the findings of digestive impact on tea catechins are likely also true for other bioactive compounds in foods. Dr. Bomser points out that the active compound in broccoli, for example, is not released until chewing and the digestive process begins. How do we formulate food to prevent degradation and perhaps enhance anti-cancer activity?
And fourth, say the researchers, the epidemiological findings of protective impact of teas rich in the unstable, easily degraded catechins may indicate that other compounds in tea are responsible, in part, for this anticancer activity. Further research is necessary to identify these compounds and to understand the impact of digestion on their anticancer activity. Funding for this work comes from the National Cancer Institute.
Green Tea's Record Against Cancer Grows
Green Tea Extract Targets Cancer Without Hurting Healthy Cells
By Miranda Hitti
WebMD Health News
Feb. 15, 2005 -- Green tea's reputation as a powerhouse against cancer keeps growing. Now, scientists have new insights on how green tea thwarts cancer. Green tea extract has shown promise against cancer in numerous studies. Those findings came from animal studies and epidemiologic research, which tracks a disease's occurrence in a large population of people.
In other words, the human studies on green tea are mainly based on observation and don't prove that tea is responsible for results. But as one of the world's most popular drinks, tea is widely considered healthy, whether it's green, black, or white tea. However, green tea and green tea supplements generally contain higher amounts of disease-fighting antioxidants called polyphenols than black tea.
For instance, studies on mice showed that green tea helped prevent prostate cancer growth. Green tea extract is also reported to induce cancer cell death and starve tumors by curbing the growth of new blood vessels that feed them.
But exactly how that happens isn't clear. Tea's antioxidants may protect against some forms of cancer. They may also help prevent heart disease by relaxing blood vessels and preventing blood clots. But the precise ways green tea affects cancer aren't fully understood.
Uncovering a Clue to Green Tea's Power University of California Los Angeles (UCLA) researchers used green tea extract on human bladder cells, some of which were cancerous.
Their findings appear in the Feb. 15 issue of Clinical Cancer Research.
The green tea extract targeted the cancer cells without harming healthy cells, say the researchers. Taking a closer look, they noticed something unusual about the cancer cells. The green tea extract apparently made the cancer cells more mature, making them bind together more closely. That made it harder for the cancer cells to become invasive and spread. "In effect, the green tea extract may keep the cancer cells confined and localized, where they are easier to treat and the prognosis is better," says researcher JianYu Rao, MD, in a news release.
That's an important clue, but it's not the final verdict on how green tea works against cancer. More work is still needed to understand the process, say the scientists. Meanwhile, if you're interested in trying green tea, be aware that the FDA hasn't evaluated claims about green tea's powers and that supplements are not regulated by the government. If you're watching your caffeine intake, green tea does contain some caffeine (but much less than coffee).
To get green tea's potential disease-fighting benefits, studies have suggested that you should drink four cups a day. Green tea supplements are also available, and at least one study has shown that you may actually get more powerful antioxidants from supplements than from drinking tea.
As always, let your doctor know about any over-the-counter health products you're taking.
Green Tea Component May Slow Prostate Cancer
Men in small study took capsules equivalent to brewed beverage
Posted June 19, 2009
FRIDAY, June 19 (HealthDay News) -- The active compounds in green tea might slow the progression of prostate cancer, the results of a small study suggest. The study included 26 men, 41 to 72 years old, who had prostate cancer and were scheduled for radical prostatectomy. The men took four capsules a day of an investigational agent called Polyphenon E, an amount equivalent to about 12 cups of normally brewed, concentrated green tea. The men took the capsules for 12 to 73 days, with a median time of 34.5 days, but stopped the day before surgery.
• The phase 2 study found "significant" reductions in the men's serum levels of markers predictive of prostate cancer progression, including hepatocyte growth factor, vascular endothelial growth factor and prostate specific antigen. In some men, reductions in levels of these markers were greater than 30 percent, the researchers found. There were few reported side effects, and the men's liver function remained normal, according to James A. Cardelli, a professor and director of basic and translational research at the Feist-Weiller Cancer Center at Louisiana State University Health Sciences Center-Shreveport, and his research colleagues. The findings are reported in Cancer Prevention Research. A recent year-long clinical trial in Italy found that consumption of green tea polyphenols reduced prostate cancer risk in men with high-grade prostate intraepithelial neoplasia, according to a news release from the American Association for Cancer Research. "These studies are just the beginning, and a lot of work remains to be done," Cardelli said in the news release. "However, we think that the use of tea polyphenols alone or in combination with other compounds currently used for cancer therapy should be explored as an approach to prevent cancer progression and recurrence." Green Tea May Slow Breast Cancer (LifeWire) - There's been a lot of talk about the benefits of drinking green tea. Among the headlines is an intriguing claim that a chemical found in the beverage may be a powerful weapon against breast cancer. But before you load up on green tea bags and start chugging away, you should learn a bit more about this alleged miracle brew and the science behind it
Green Tea
Photo ©
Pam Stephan
Antioxidants and Free Radicals
Green tea's cancer-fighting reputation comes from its polyphenols, chemicals that have antioxidant properties. Antioxidants protect the cells in your body from free radicals, highly reactive molecules that speed the damage caused by chemicals in the environment or aging, which can lead to the development of cancer. Other examples of antioxidants include lycopene, found in cooked tomatoes, and vitamin A, found in carrots.
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