The US Cancer institute has published fact sheet entitled ‘tea and cancer prevention’, the key points are featured below. It seems to refelct very positively that green tea consumption aids cancer prevention.

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.

1. What are antioxidants?

The human body constantly produces unstable molecules called oxidants, also commonly referred to as free radicals. To become stable, oxidants steal electrons from other molecules and, in the process, damage cell proteins and genetic material. This damage may leave the cell vulnerable to cancer. Antioxidants are substances that allow the human body to scavenge and seize oxidants. Like other antioxidants, the catechins found in tea selectively inhibit specific enzyme activities that lead to cancer. They may also target and repair DNA aberrations caused by oxidants (1).

2. What is the level of antioxidants found in tea?

All varieties of tea come from the leaves of a single evergreen plant, Camellia sinensis. All tea leaves are picked, rolled, dried, and heated. With the additional process of allowing the leaves to ferment and oxidize, black tea is produced. Possibly because it is less processed, green tea contains higher levels of antioxidants than black tea.

Although tea is consumed in a variety of ways and varies in its chemical makeup, one study showed steeping either green or black tea for about five minutes released over 80 percent of its catechins. Instant iced tea, on the other hand, contains negligible amounts of catechins (1).

3. What are the laboratory findings?

In the laboratory, studies have shown tea catechins act as powerful inhibitors of cancer growth in several ways: They scavenge oxidants before cell injuries occur, reduce the incidence and size of chemically induced tumors, and inhibit the growth of tumor cells. In studies of liver, skin and stomach cancer, chemically induced tumors were shown to decrease in size in mice that were fed green and black tea (1, 2).

4. What are the results of human studies?

Although tea has long been identified as an antioxidant in the laboratory, study results involving humans have been contradictory. Some epidemiological studies comparing tea drinkers to non-tea drinkers support the claim that drinking tea prevents cancer; others do not. Dietary, environmental, and population differences may account for these inconsistencies.

Two studies in China, where green tea is a mainstay of the diet, resulted in promising findings. One study involving over 18,000 men found tea drinkers were about half as likely to develop stomach or esophageal cancer as men who drank little tea, even after adjusting for smoking and other health and diet factors (3). A second study at the Beijing Dental Hospital found consuming 3 grams of tea a day, or about 2 cups, along with the application of a tea extract reduced the size and proliferation of leukoplakia, a precancerous oral plaque.

5. Is NCI evaluating tea?

National Cancer Institute (NCI) researchers are also investigating the therapeutic use of green tea. One recently completed but unpublished NCI trial studied the antitumor effect of green tea among prostate cancer patients. The 42 patients drank 6 grams of green tea, or about 4 cups, daily for four months.

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.

Clinical trials conducted by the University of Geneva and the University of Birmingham indicate that green tea raises metabolic rates, speeds up fat oxidation and improves insulin sensitivity and glucose tolerance, thus aiding weight loss. In addition to caffeine, green tea contains catechin polyphenols that raise thermogenesis (the rate at which calories are burned), and hence increases energy expenditure.

There is also a suggestion that it can increase endurance in exercise by improving fat metabolism.

According to research reported at the Sixth International Conference on Frontiers in Cancer Prevention, sponsored by the American Association for Cancer Research, a standardized green tea polyphenol preparation (Polyphenon E) limits the growth of colorectal tumors in rats treated with a substance that causes the cancer. “Our findings show that rats fed a diet containing Polyphenon E are less than half as likely to develop colon cancer,” Dr. Hang Xiao, from the Ernest Mario School of Pharmacy at Rutgers University, Piscataway, New Jersey, noted in a statement.

A 2006 study published in the September 13 issue of the Journal of the American Medical Association concluded “Green tea consumption is associated with reduced mortality due to all causes and due to cardiovascular disease but not with reduced mortality due to cancer.” The study, conducted by the Tohoku University School of Public Policy in Japan, followed 40,530 Japanese adults, ages 40-79, with no history of stroke, coronary heart disease, or cancer at baseline beginning in 1994. The study followed all participants for up to 11 years for death from all causes and for up to 7 years for death from a specific cause. Participants who consumed 5 or more cups of tea per day had a 16 percent lower risk of all-cause mortality and a 26 percent lower risk of cardiovascular disease than participants who consumed less than one cup of tea per day. The study also states, “If green tea does protect humans against CVD or cancer, it is expected that consumption of this beverage would substantially contribute to the prolonging of life expectancy, given that CVD and cancer are the two leading causes of death worldwide.”

A study in the February 2006 edition of the American Journal of Clinical Nutrition concluded “A higher consumption of green tea is associated with a lower prevalence of cognitive impairment in humans.”

In May 2006, researchers at Yale University School of Medicine weighed in on the issue with a review article that looked at more than 100 studies on the health benefits of green tea. They pointed to what they called an “Asian paradox,” which refers to lower rates of heart disease and cancer in Asia despite high rates of cigarette smoking. They theorized that the 1.2 liters of green tea that is consumed by many Asians each day provides high levels of polyphenols and other antioxidants. These compounds may work in several ways to improve cardiovascular health, including preventing blood platelets from sticking together (This anticoagulant effect is the reason doctors warn surgical patients to avoid green tea prior to procedures that rely on a patient’s clotting ability) and improving cholesterol levels, said the researchers, whose study appeared in the May issue of the Journal of the American College of Surgeons. Specifically, green tea may prevent the oxidation of LDL cholesterol (the “bad” type), which, in turn, can reduce the buildup of plaque in arteries, the researchers wrote.

A study published in the August 22, 2006 edition of Biological Psychology looked at the modification of the stress response via L-Theanine, a chemical found in green tea. It “suggested that the oral intake of L-Theanine could cause anti-stress effects via the inhibition of cortical neuron excitation.”

In a double-blind, randomized, placebo-controlled trial done by Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, 240 adults were given either theaflavin-enriched green tea extract in form of 375mg capsule daily or a placebo. After 12 weeks, patients in the tea extract group had significantly less low-density lipoprotein cholesterol (LDL-C) and total cholesterol (16.4% and 11.3% lower than baseline, p<0.01) than the placebo group. The author concluded that theaflavin-enriched green tea extract can be used together with other dietary approaches to reduce LDL-C.

A study published in the January, 2005 edition of the American Journal of Clinical Nutrition concluded “Daily consumption of tea containing 690 mg catechins for 12 wk reduced body fat, which suggests that the ingestion of catechins might be useful in the prevention and improvement of lifestyle-related diseases, mainly obesity.”

According to a Case Western Reserve University School of Medicine study published in the April 13 2005 issue of the Proceedings of the National Academy of Sciences, antioxidants in green tea may prevent and reduce the severity of rheumatoid arthritis. The study examined the effects of green tea polyphenols on collagen-induced arthritis in mice, which is similar to rheumatoid arthritis in humans. In each of three different study groups, the mice given the green tea polyphenols were significantly less likely to develop arthritis. Of the 18 mice that received the green tea, only eight (44 percent) developed arthritis. Among the 18 mice that did not receive the green tea, all but one (94 percent) developed arthritis. In addition, researchers noted that the eight arthritic mice that received the green tea polyphenols developed less severe forms of arthritis.

A German study found that an extract of green tea and hot water (filtered), applied externally to the skin for 10 minutes, three times a day could help people with skin damaged from radiation therapy (after 16-22 days).

A study published in the December 1999 American Journal of Clinical Nutrition found that “Green tea has thermogenic properties and promotes fat oxidation beyond that explained by its caffeine content per se. The green tea extract may play a role in the control of body composition via sympathetic activation of thermogenesis, fat oxidation, or both.”

In lab tests, EGCG, found in green tea, was found to prevent HIV from attacking T-Cells. However, it is not yet known if this has any effect on humans.

A study in the August, 2003 issue of a new potential application of Cellular and Molecular Life Sciences found that “a new potential application of (–)-epigallocatechin-3-gallate [a component of green tea] in prevention or treatment of inflammatory processes is suggested”.

However, pharmacological and toxicological evidence does indicate that green tea polyphenols can in fact cause oxidative stress and liver toxicity in vivo at certain concentrations.  This would imply that consumers should exercise caution when consuming herbal products produced from concentrated green tea extract. Other evidence presented in the review cautions against the drinking of green tea by pregnant women.

In the normal human life span, there occur lifestyle-related diseases that may be preventable with nontoxic agents. This paper deals with the preventive activity of green tea in some lifestyle-related diseases. Green tea is one of the most practical cancer preventives, as we have shown in various in vitro and in vivo experiments, along with epidemiological studies. Among various biological effects of green tea, we have focused on its inhibitory effect on TNF- gene expression mediated through inhibition of NF-B and AP-1 activation.

Based on our recent results with TNF–deficient mice, TNF- is an endogenous tumor promoter. TNF- is also known to be a central mediator in chronic inflammatory diseases such as rheumatoid arthritis and multiple sclerosis. We therefore hypothesized that green tea might be a preventive agent for chronic inflammatory diseases. To test this hypothesis, TNF- transgenic mice, which overexpress TNF- only in the lungs, were examined. The TNF- transgenic mouse is an animal model of human idiopathic pulmonary fibrosis which also frequently develops lung cancer. Expressions of TNF- and IL-6 were inhibited in the lungs of these mice after treatment with green tea in drinking water for 4 months. In addition, judging from the results of a prospective cohort study in Saitama Prefecture, Japan, green tea helps to prevent cardiovascular disease. In this study, a decreased relative risk of death from cardiovascular disease was found for people consuming over 10 cups of green tea a day, and green tea also had life-prolonging effects on cumulative survival. These data suggest that green tea has preventive effects on both chronic inflammatory diseases and lifestyle-related diseases (including cardiovascular disease and cancer), resulting in prolongation of life span.

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.

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.”

Generally, 2.25 grams of tea per 6 ounces of water, or about one teaspoon of green tea per cup, should be used. With very high quality teas like gyokuro, more than this amount of leaf is used, and the leaf is steeped multiple times for short durations.

Green tea brewing time and temperature varies with individual teas. The hottest brewing temperatures are 180°F to 190°F (82°C to 88°C) water and the longest steeping times 2 to 3 minutes. The coolest brewing temperatures are 140°F to 150°F (60°C to 66°C) and the shortest times about 30 seconds. In general, lower quality green teas are steeped hotter and longer, while higher quality teas are steeped cooler and shorter. Tea Masters living in China nowadays say that boiling water must be used all the time even with green teas due to the fact that high quality leaves can handle higher temperatures very well. Steeping green tea too hot or too long will result in a bitter, astringent brew for low quality leaves. High quality green teas can be and usually are steeped multiple times; 2 or 3 steepings is typical. The brewing technique also plays a very important role to avoid the tea develop an overcooked taste. If a tea claims to be high grade but the vendor instructions says that boiling water mustn`t be used then there is a chance that the tea is not so high grade.

The Chinese have known about the medicinal benefits of green tea since ancient times, using it to treat everything from headaches to depression.

In fact Chinese Green tea has been researched and linked to help all of the following conditions.

* rheumatoid arthritis
* high cholesterol levels
* cariovascular disease
* infection
* impaired immune function
* Cognition
* Stopping certain neurodegenerative illnesses such as Alzheimers
* Treating Arthritis
* Treating MS

Preventing lowered T-Cells due to HIV
In lab tests, EGCG, found in green tea, was found to prevent HIV from attacking T-Cells. Scientists in Japan have found a component of green tea can stop HIV from binding to healthy immune cells, which is how the virus spreads.Their laboratory tests suggest a chemical called Epigallocatechin Gallate (EGCG) protects cells. Writing in the Journal of Allergy and Clinical Immunology, the scientists said the discovery could lead to new treatments to fight the disease. Although it is not known if this has any effect on humans yet.

Cancer
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. In fact they said many laboratory studies have demonstrated inhibitory effects of tea preparations and tea polyphenols against tumor formation and growth. This inhibitory activity is believed to be mainly due to the antioxidative and possible antiproliferative effects of polyphenolic compounds in green and black tea.

Weight Loss
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 Increases fat oxidation (helps the body use fat as an energy source) and raises metabolism. These are two things that are predictive of weight loss.

Teeth and Skin
Meanwhile, skin preparations containing green tea – from deodorants to creams – are starting to appear on the market. Scientists have even discovered that applying green tea to the skin can help cure and prevent some forms of skin cancer and other skin disorders, protect the skin from long- and short-term damage from the sun�s ultraviolet rays, and act as an antibacterial agent when applied to skin infections. Many of the broad health benefits of green tea are derived from its rich supply of plant nutraceuticals called polyphenols, of which epigallocatechin gallate (EGCG) is the most powerful.A respite for parents of children consuming too much chocolates have reason to cheer up. The consumption of green tea has been linked to reduced incidence of tooth decay.

How does Green Tea Work?
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. The reason Green tea & White Tea have more polyphenol antioxidants than other teas is because of the way they are processed. Preventing the degradation of cell membranes by neutralizing the spread of free radicals (which occurs during the process of oxidation). The health benefits of these teas are derived from the light processing of the leaves which maintain the ingredients like Catechin that research is now demonstrating to be beneficial. White & Green tea are often steamed or pan fired rather than being semi-fermented (oolong) or fermented (black tea). Fermentation leaches out some of these beneficial ingredients in the same way that frying food tends to reduce nutrient value that steaming does not. It should be no surprise that steamed green tea also maintains more of its polyphenol antioxidant profile than pan-fired green tea as well.