The Benefits of Green Tea

by Mike July 13, 2011

Green tea consumption is associated with reduced heart disease in epidemiological studies.

Green tea is made solely with the leaves of Camellia sinensis that have undergone minimal oxidation during processing. Green tea originates from China and has become associated with many cultures in Asia from Japan and South Korea to the Middle East. Recently, it has become more widespread in the West, where black tea is traditionally consumed. Many varieties of green tea have been created in countries where they are grown. These varieties can differ substantially due to variable growing conditions, horticulture, production processing, and harvesting time.

Over the last few decades green tea has been subjected to many scientific and medical studies to determine the extent of its long-purported health benefits, with some evidence suggesting that regular green tea drinkers have lower chances of heart disease and of developing certain types of cancer. Although green tea does not raise the metabolic rate enough to produce immediate weight loss, a green tea extract containing polyphenols and caffeine has been shown to induce thermo genesis and stimulate fat oxidation, boosting the metabolic rate 4% without increasing the heart rate.

According to a survey released by the United States Department of Agriculture in 2007, the mean content of flavonoids in a cup of green tea is higher than that in the same volume of other food and drink items that are traditionally considered of health contributing nature, including fresh fruits, vegetable juices or wine. Flavonoids are a group of phytochemicals in most plant products that are responsible for such health effects as anti-oxidative and anticarcinogenic functions. However, as a tea information site points out, the content varies dramatically amongst different tea products, basing on the same USDA survey.

All real tea comes from the Camellia Sinensis leaf. Green tea (lu cha) is the result of curing the young camellia leaf using various methods and degrees of heat. Some green tea is cured with ovens, while others are pan-fried in a giant wok called a ding.

Steeping:

Steeping is the process of making a cup of tea; it is also referred to as brewing. Generally, two grams of tea per 100ml of water, or about one teaspoon of green tea per five ounce 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 steeping time and temperature varies with different tea. The hottest steeping temperatures are 81°C to 87°C (180°F to 190°F) water and the longest steeping times two to three minutes. The coolest brewing temperatures are 61°C to 69°C (140°F to 160°F) 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. Steeping green tea too hot or too long will result in a bitter, astringent brew, regardless of the initial quality. It is thought that excessively hot water results in tannin chemical release, which is especially problematic in green teas as they have higher contents of these. High quality green teas can be and usually are steeped multiple times; two or three steepings is typical. The steeping technique also plays a very important role in avoiding the tea developing an overcooked taste. Preferably, the container in which the tea is steeped or teapot should also be warmed beforehand so that the tea does not immediately cool down. It is common practice for tea leaf to be left in the cup or pot and for hot water to be added as the tea is drunk until the flavor degrades.

Health effects:

Green tea contains salubrious polyphenols, particularly catechins, the most abundant of which is epigallocatechin gallate. Green tea also contains carotenoids, tocopherols, ascorbic acid (vitamin C), minerals such as chromium, manganese, selenium or zinc, and certain phytochemical compounds. It is a more potent antioxidant than black tea, although black tea has substances which green tea does not such as theaflavin.

In vitro, animal, preliminary observational, and clinical human studies suggest that green tea can reduce the risk of cardiovascular disease, dental cavities, kidney stones, and cancer, while improving bone density and cognitive function. However, the human studies are inconsistent.

Green tea consumption is associated with reduced heart disease in epidemiological studies. Animal studies have found that it can reduce cholesterol. However, several small, brief human trials found that tea consumption did not reduce cholesterol in humans. In 2003 a randomized clinical trial found that a green tea extract with added theaflavin from black tea reduced cholesterol.

A study performed at Birmingham (UK) University, showed 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 implies 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.

A study performed at the Queen Margaret University, Edinburgh looked at the effects of short-term green tea consumption on a group of students between the ages of 19–37. Participants were asked not to alter their diet and to drink 4 cups of green tea per day for 14 days. The results showed that short-term consumption of commercial green tea reduces systolic and diastolic Blood Pressure, fasting total cholesterol, body fat and body weight. These results suggest a role for green tea in decreasing established potential cardiovascular risk factors. This study also suggests that reductions may be more pronounced in the overweight population where a significant proportion are obese and have a high risk of cardiovascular disease.

In a study performed at the Israel Institute of Technology, it was shown that the main antioxidant polyphenol of green tea extract, EGCG, when fed to mice induced with Parkinson's and Alzheimer's disease, helped to protect brain cells from dying, as well as 'rescuing' already damaged neurons in the brain, a phenomenon called neurorescue or neurorestoration. The findings of the study, led by Dr. Silvia Mandell, were presented at the Fourth International Scientific Symposium on Tea and Human Health in Washington D.C., in 2007. Resulting tests underway in China, under the auspices of the Michael J. Fox Foundation, are being held on early Parkinson's patients.

A study  performed at the National institute of Chemistry in Ljubljana, Slovenia, demonstrated that EGCG from green tea inhibits an essential bacterial enzyme gyrase by binding to the ATP binding site of the B subunit. This activity probably contributes to the antimicrobial activity of green tea extract and may be responsible for the effectiveness of green tea in oral hygiene.

In a recent case-control study of the eating habits of 2,018 women, consumption of mushrooms and green tea was linked to a 90% lower occurrence of breast cancer.

A recent study on rats at the University of Hong Kong, published in the February issue of Journal of Agricultural and Food Chemistry, found that the catechins in green tea were absorbed by the lens, retina and other parts of the eye. The absorbed catechins reduced oxidative stress in the eye for up to 20 hours, suggesting that green tea may be effective in preventing glaucoma and other diseases of the eye.

History:

Tea consumption has its legendary origins in China of more than 4,000 years ago. Green tea has been used as both a beverage and a method of traditional medicine in most of Asia, including China, Japan, Taiwan, Vietnam, Korea 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.

Scientific studies:

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 study published in the September 13, 2006 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 ("CVD") 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 conducted by Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Nashville, Tennessee; 240 adults were given either theaflavin-enriched green tea extract in form of 375 mg 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.

A more frequent consumption of green tea was associated with a lower prevalence of depressive symptoms in a Japanese study. Researchers conducted a cross-sectional study in 1,058 community-dwelling elderly Japanese individuals 70 years of age. The prevalence of mild and severe depressive symptoms was 34.1 percent and 20.2 percent, respectively. After adjustment for confounding factors, the odds ratios for mild and severe depressive symptoms when higher green tea consumption was compared with green tea consumption of 1 cup/d were: 2 to 3 cups green tea/d and 4 cups green tea/d. Similar relations were also observed in the case of severe depressive symptoms.

Drug interactions

A 2009 study at the University of Southern California using mouse models showed that several of the polyphenolic ingredients of green tea, such as EGCG, can bind with the anticancer drug bortezomib, significantly reducing its bioavailability and thereby rendering it therapeutically useless. This chemical reaction between EGCG and bortezomib is highly specific and depends on the presence of a boronic acid functional group in the bortezomib molecule. Dr. Schönthal, who headed the study, suggests that consumption of green tea, concentrated green tea extract, and other green tea products (such as EGCG capsules) be strongly contraindicated for patients undergoing bortezomib treatment. Use of green tea in conjunction with anticoagulants may result in reduced effectiveness; there is a correlation between the quantity of tea consumed and the method of production may affect the amount of Vitamin K.

Caffeine:

Unless specifically decaffeinated, green tea contains caffeine. While coffee and tea are both sources of caffeine, the amount of caffeine in any single serving of these beverages varies significantly. An average serving of brewed coffee contains 145 mg of caffeine, the same serving size of green tea provides 25 mg (black tea provides 47–60 mg and white tea 15 mg). One of the more confusing aspects of caffeine content is the fact that while coffee contains less caffeine than tea when measured in its dry form, the caffeine content of a prepared cup of coffee is significantly higher than the caffeine content of a prepared cup of tea.

Green tea extract:

Types of green tea extracts:

Strong infusions:

During the strong infusion green tea leaves are processed by soaking in the aqueous solution of alcohol (the aspect content is about 2% w/w.)

Soft extracts:

To obtain soft extracts, the solution made by strong infusion beforehand is further concentrated to 20–25% (the catechin content is about 20% w/w.)

Dry extracts:

After the strong infusions have been concentrated to 40–50% solids (the catechin content is above 25% w/w)?they are sprayed and then become dehydrated extract and powder. The leftovers - water content, which is less than 5% w/w, and the extract - are usually processed as a powder containing inert processing aids to become suitable for a variety of uses (tablets, capsules, dry mixes, etc.)

Partly purified extracts:

Further purification processes, for example, solvent extraction or column chromatography techniques, as well as new techniques such as membrane extraction and separation, are utilized in order to acquire a higher content of tea catechins.

They can also be called green tea polyphenols: (GTP or GTPs). The category includes epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG) and epicatechin (EC). Of which, EGCG accounts for more than 40% of the total content.

Chemistry and Biochemistry:

Constituents:

The cardinal antioxidative ingredient in the green tea extract is green tea catechins (GTC), which comprise four major epicatechin derivatives; namely, epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG).

Other components include three kinds of flavonoids, known as kaempferol, quercetin, and myricetin. A remarkably higher content of myricetin is detected in tea and its extracts than in many other plants, and this high concentration of myricetin may have some implications with the bioactivity of tea and its extracts.

Caffeine may be excluded in green tea extracts in order to avoid side-effects; caffeine-free green tea extract supplements are available nowadays.

Chemical properties:

Green tea extract is 20 times more antioxidant-active than Vitamin C. The main attribution is supposed to be EGCG.

In alkaline solutions (pH > 9 to 10) GTC (green tea catechins) .

Biochemical properties:

The biochemical properties of green tea extracts can be generally divided into four aspects – antioxidant, anti carcinogen, anti-inflammatory, and anti-radiation.

Green tea extracts exhibit stronger antioxidant protection for human body than vitamin C and vitamin E. Scavenging effect of lipid free-radicals (one antioxidant property) of polyphenols in green tea extracts can be clearly observed in experiments. The ability of GTP in green tea extracts to eliminate lipid-derived free radicals is noticeably stronger (almost 50 times) than that of ginkgo biloba extracts. Further investigations indicate that the boosting level of superoxide dismutase (SOD) and glutathione dismutase (GSHPx) may account for the inhibitory effect of GTC against lipid oxidation (rancidification). It should be mentioned that from the antioxidant perspective, green tea extracts are, generally speaking, more effective than black tea extracts due to the better preservation of catechins.

Moreover, the anticarcinogenic property make the green tea extracts a hotspot in recent scientific researches. In many experiments, green tea extracts show inhibitory effects on cancer cells. In vitro assays, Catechin and caffeine, which are main components in green tea extracts, block the cell cycle of cancer cells (cytotoxicity) and induce programmed cell death; in vivo, green tea extracts also inhibits prostatic carcinoma transplanted in nude mice

In addition, green tea extracts also contain a wide-ranged anti-inflammatory characteristics, so it may be helpful in treating chronic inflammatory states. The bactericidal activity against S.mutans is conspicuous in Japanese green tea extracts, and the maltose level in mouth is consistently lower after drinking tea. Therefore, green tea extracts may be effective in oral hygiene maintenance. Green tea extracts show anti-radiation properties on white rats in radioactive isotope experiments

Dosage and Side-effects:

Green tea extract supplements are accessible over the counter in various forms. Standardized green tea extract is 90 percent total polyphenols, and 1 capsule equals 5 cups of tea. For a green tea extract standardized for 80 percent polyphenols and 55 percent EGCG, a daily dose of 300 to 400 mg green tea extracts is recommended [6]. Some green tea extracts may have as little as 15 percent polyphenols, usually these are far less expensive. It should be kept in mind that the various components of unpurified green tea extracts have synergistic effects and therefore are better than any individual tea component. Scientists also conclude that tea extracts are better taken between meals in order to avoid decreased iron absorption.

Though green tea extracts show potential anticancer capacity - under some conditions by working together with other drugs and suppressing multidrug resistance in cancer cells - they are not suggested for use alone as a chemotherapy agent for cancer treatment .

Excessive intake of green tea extracts containing caffeine has side effects; an excessive concentration may act as a pro-oxidant to damage DNA and produce undesirable side effects

Skin Care:

Organic certified green tea extracts are used for their natural anti oxidants and anti aging properties in skin care products as a natural component of anti wrinkle, natural anti aging, miracle lift  and a fragrance material in natural skin care.

Food additive and deodorant applications:

Because of the high antioxidant activity of green tea extracts, they are hopefully to be used as a kind of innovative food additive to preserve pork, chicken meat, vegetable oil, fish oil and fish flesh, food emulsions and animal fat. This alternative antioxidant is suggested to be a healthier choice; a fairly successful instance may well be the application in Moon cake – the extracts both increase the shelf life and improve the flavor.

In addition, green tea extracts are a promising solution to prevent apple juice and other foods from microbial contamination. Japanese scientists even have discovered that tea extracts can be developed as dyes that are not susceptible to microbial contamination and possess strong deodorant activity.

More information:

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