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Green Tea

Green Tea Current Research on Health Benefits as a Complementary Medicine
by

Julie Stefanski

on 23 April 2010

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Transcript of Green Tea

Green Tea Scientific Background
Green tea comes from the evergreen shrub: camellia sinensis
Green tea is nonfermented and is made by drying and steaming the tea leaves
Tea plant buds and two adjacent leaves are used during the drying process

Green tea has a high content of flavonoids (plant derived antioxidants).
Green tea is made of polyphenolic compounds mainly catechins.
(Wang et al. 2009)

Green tea also has components of carotenoids, tocopherols, ascorbic acid (vitamin C), minerals such as Cr, Mn, Se or Zn, and certain phytochemical compounds.
(Cabrera 2006)
Phenolics in a green tea (Camellia sinensis)
(-)-Epigallocatechin gallate
(-)-Epigallocatechin
(-)-Epicatechin
(-)-Epicatechin gallate
(+)-Catechin
(+)-Gallocatechin
(Moore 2009) These catechins are easily oxidized making them better antioxidants. These units react with oxidants as free radical reactive oxygen species. The high content of polyphenolic compounds make green tea polyphenols excellent antioxidants for scavenging free radicals and inhibiting lipid formation.
(Zaveri 2006) Catechins found in green tea are present in higher quantities than in black or oolong tea. The drying and steaming of green tea leaves inactivate the polyphenol oxidase enzyme, this process maintains the polyphenols in monomeric forms. The process of fermenting black tea changes the polyphenols to polymeric compounds
(Zaveri 2006)
Green tea has been consumed throughout the ages in India, China, Japan, and Thailand. In traditional Chinese and Indian medicine, practitioners used green tea as a stimulant, diuretic (to promote the excretion of urine), astringent (to control bleeding and help heal wounds), and to improve heart health. Other traditional uses of green tea include treating flatulence (gas), regulating body temperature and blood sugar, promoting digestion, and improving mental processes.
UMD Medical Center Possible Health Benefits Catechins have an effect on signal transduction pathways associated with cell death and survival (seen in studies in vitro with excessive concentrations of EGCG)
Properties of inhibiting tumor cell proliferation
Serve as a neuorprotective prosurvival function
Antioxidant properties because of polyphenol makeup
Anti-hypertensive effects and cardiovascular disease risk
green tea may have thermogenic properties not only attributable to caffeine content, but to the reaction of caffeine and catechins together (weight management)
Anti-inflammatory and antibacterial effect
topical protector agent against some types of radiation, since it prevents skin disease, photoaging and potential cancer problems due to prolonged exposure
(Cabrera 2006)




Issues of Research There is considerable intra- and inter-study variability which is likely attributable to study design and population characteristics including genetics and environmental factors. (Moore 2009)
Green tea has low bioavailability of polyphenolic catechins after drinking green tea.(Chow et al. 2001) Bioavailability is low due to instability under digestive conditions, poor absorption, and rapid metabolism and excretion, leading to only about 5% of consumed catechins appearing in the plasma on average
Repeated conflict of conclusions based on in vitro and in vivo studies. Concentrations of green tea extracts used in in vitro studies are usually much higher than the doses consumed by humans.
Many epidemiologocial studies do not control for factors that may influence data.
Cultural differences in green tea consumption alter the reliability in human responses worldwide.
Can't assume results from certain pathologies will be consistent with others. Especially with cancer studies, one type of cancer may be more susceptible to having an effect from green tea, while another type of cancer may not.




FDA "There is no credible scientific evidence to support qualified health claims about consumption of green tea or green tea extract and a reduction of a number of risk factors associated with CVD."
2006

FDA identified 18 intervention studies for its evaluation of the relationship between green tea consumption and risk of CVD.
Scientific conclusions could not be drawn from 13 studies regarding the substance/disease relationship
Reasons: 9 studies did not include valid endpoints to measure risk of CVD, 2 studies did not include control groups, 1 study did not have a statistical analysis between control group and treatment group


Cochrane Review Green tea (Camellia sinensis) for the prevention of cancer fifty-one studies included with 1.6 million people
Most of the studies were observational in nature
Studies looked at association between consumption of green tea and cancer of digestive tract, gynecological cancer, breast cancer, urological cancer, lung cancer, cancer of oral cavity
Studies were medium to high methodological quality
Conclusion: conflicting data Pathologies Cardiovascular Disease
Reviews: Epidemiological Studies- not significant effect on vascular funtion
Acute trials have more positive results. GTE thought to help control cholesterol levels.
Meta analysis results:— Regardless of their country of origin, individuals consuming >=3 cups of tea per day had a 21% lower risk of stroke than those consuming <1 cup per day . The proportion of heterogeneity not explained by chance alone was 23.8%.
This analysis included case control trials and epidemiological trials
(Arab et al. 2008)
More than half of RCT have demonstrated a beneficial effect of green tea on CVD risk. However, the other trials do not show these effects. Long term RCT are needed.

Ohsaki NHI Cohort Study correlations: .63 for men, .64 for women for cause-specific mortality.
(Kuriyama 2006)
Current research….in vivo studies on rats looking at how tea catechin extract prevents development of atherosclerosis and EGCD reduces progression of disease.
Atherosclerosis
(Naito 2009)
Cancer Meta-analysis for association between green and black tea on lung cancer. Results show a reduced risk of lung cancer with consumption of higher doses of green tea. No significant association with black tea.
Tang 2009 Results of a meta-analysis of 14 epidemiological studies indicates that there is no clear epidemiological evidence supporting the suggestion that green tea plays a role in the prevention of gastric cancer.
Yong 2008 Dietary flavonoids have low bioavailability and may interact with chemotherapeutic drugs used in treatment though inhibition of metabolism. American Cancer Research: Green tea catechins control the unwanted proliferation of cells (becoming chemopreventative)
American Cancer Research: GTE's safe and effective for treating premalignant lesions before development of prostate cancer. Weight Management Problems of reported toxicity in weight loss supplements including GTE. 7-8 cups of tea = 120 ml x 3 daily. Case studies of severe hypertoxicity- Jaundice, liver damage. Some diet pills have been taken off the market because of hepatotoxicity.
(Yin 2009) EGCG has been shown to reduce food intake,
plasma levels of glucose, and body weight RCT's slight decrease in body mass, increase in energy expenditure and fat oxidation.
(Chung 2003) One study looked at caffeine versus decaffeinated GTE, benefit still seen in decaffeinated GTE.
(Takeshita 2008) Conclusions of Evidence According to the testing effectiveness hierarchy meta analysis are the highest. The meta analysis found for most pathologies are conflicting. Throughout literature there was low significance for effectiveness in some specific cancers.
The RCT's are present in literature, however the lack of long term RCT's question the evidence.
In laboratory studies the experiments include dosage of GTE much higher than that consumed by humans.
In laboratory studies the mechanism of action is not always clear.

Although research of green tea is very promising, future studies considering dietetic, environmental and life style factors, are necessary to fully understand its contribution to human health.
Carmen Cabrera
What should green tea be used for? At this time scientific evidence suggest efficacy for many different pathologies. Throughout literature consuming green tea in its natural form shows no adverse effects.
Warnings about GTE in diet pills are related to the high dosage of catechins that have been seen rarely to show hypertoxicity incidences.
Consuming green tea is an excellent way to incorporate antioxidants in a healthy diet.
The ritualistic benefits of tea drinking have also been studied suggesting a calming and relaxing experience.
Until RCT's and epidemiological studies are consistent green tea should not be a primary treatment for a number of pathologies. What the Science Says
Laboratory studies suggest that green tea may help protect against or slow the growth of certain cancers, but studies in people have shown mixed results.
Some evidence suggests that the use of green tea preparations improves mental alertness, most likely because of its caffeine content. There are not enough reliable data to determine whether green tea can aid in weight loss, lower blood cholesterol levels, or protect the skin from sun damage.
NCCAM is supporting studies to learn more about the components in green tea and their effects on conditions such as cancer, diabetes, and heart disease.
NCCAM Views Green Tea
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