REVIEW- GREEN TEA : HEALTH BENEFITS
Ambika chauhan and Intelli
E mail - ambikachauhan671@yahoo.com
Abstract
The plant Camellia sinensis yields a variety of white, green and black tea. Tea is one of the most
widely consumed beverages in the world, next only to water for enjoyment and health. In
general, green tea has been found to be superior to black tea in terms of health benefits. The
major components of interest are the polyphenols which are responsible for the antioxidant and
other health benefits of green tea. The major polyphenols in green tea are flavonoids. The four
major flavonoids in green tea are the catechins, epicatechin (EC), epigallocatechin (EGC),
epicatechin gallate (ECG) and epigallocatechin gallate (EGCG). Epigallocatechin gallate is
viewed as the most significant active component. Much research is available depicting the health
benefits of green tea for a wide variety of implications, including different types of heart disease,
etc. There is also a wide range of uses for green tea in cardiac, thermogenesis. This paper will
review the major health benefits of green tea and its effects to control cardiac events.
Key words: Green tea, catechins, EGCG, health benefits, polyphenols.
Introduction
Obesity is a major public health problem in developed countries as well as in developing
countries (Popkin and Doak,1998). The prevalence of obesity is steadily increasing and has
more than doubled since 1980. According to World Health Organization (WHO) global
estimates
from
2008,
over
500
million
adults
are
obese
(http://www.who.int/
mediacentre/factsheets/fs311/en). Obesity is becoming leading risk for global deaths. At least 2.8
million adults die each year as a result of being overweight or obese. With severe obesity, over
30 kg/m2 body mass index (BMI), mortality is substantially elevated by 50-150 per cent
(Sjöström ,1992). In addition, obesity is strongly associated with the development of serious
diseases such as type 2 diabetes mellitus, cardiovascular diseases, and certain cancers (Lavie et
al. 2009; Steppan et al.2001; Calle and Kaaks, 2004) . Obesity has many causes including
excessive intake of calories, genetic factors, endocrine dysfunction, metabolic disorders, and
stresses (Racette et al. 2003). Among these causes, excessive energy intake is the most common
risk factor of obesity. The major dietary fat, triglycerides (TG), provide the major source of
energy. TG is transported in the blood as lipoproteins and stored in adipose tissues (Smith and
Marks,2004). To treat obesity, constant control of diet and exercise are required (Curioni and
Lourenço,2005). However, it is hard for obese patients to maintain regular exercising steadily.
Synthetic appetite suppressants or fat absorption blockers have been developed as anti-obesity
drugs, yet the efficacy and long-term safety level of the drugs were not fully evaluated (Cooke
and Bloom,2006 ;Ioannides et al. 2006). Therefore, safe and efficient antiobesity substances are
still needed. Green tea contains a series of polyphenols known as catechins (Murase et al. 2002).
It is known that tea catechins modulate appetite and reduce food intake through the leptin
receptor-independent pathway in rats (Wolfram et al.2006). Also, green tea components have
been reported to possess various biological and pharmacological effects, such as lowering of
plasma lipids and glucose levels (Ashida et al. 2004).
Obesity
Obesity: What is it?
Overweight and obesity are both labels for
ranges of weight that are greater than what
is generally considered healthy for a given
height.
How is it determined?
For adults, overweight and obesity ranges are
determined by using weight and height to calculate a
“body mass index” or BMI. This index correlates
well with the amount of body fat that a person has.
An adult with a BMI between 25 and 29.9 is
considered overweight.
An adult with a BMI of 30 or higher is considered
obese.
Green tea help to control obesity:
Green tea composition
The chemical composition of green tea is complex; there are proteins (15% to 20% of dry
weight) including enzymes, amino acids (1% to 4% of dry weight), carbohydrates (5% to 7%
of dry weight), lipids, such as linoleic and α-linolenic acids,
sterols, vitamins (B, C, E),
xanthenes, such as caffeine and theophylline, pigments, such as chlorophyll and carotenoids,
volatile compounds, such as aldehydes, and minerals and trace elements 5% of dry weight(
Cabrera et al. 2006).
How tea works in the body
Tea contains hundreds, if not thousands, of bioactive compounds,
including amino acids,
caffeine, lignins, proteins, xanthines and flavonoids. Tea flavonoids and the related polyphenols
account for more than one-third of the weight of tea leaves; the health benefits of tea are most
often attributed to tea flavonoids. Tea flavonoids are bioactive compounds that have specific
cellular
targets that are related to the cardiovascular, chemopreventive,
metabolic,
neuroprotective and other health benefits. Recent research has explored the potential health
attributes of tea through human clinical trials, population-based studies, and in vitro laboratory
research. Additional research suggests tea flavonoids and related bioactive compounds in tea
may play important roles in various areas of health and may operate through a number of
different mechanisms still being explored (Balentine et al.1997).
Human studies confirm green tea effect
Additional human studies support green tea’s ability to boost metabolism and support healthy
weight management. A study published in the American Journal of Clinical Nutrition found that
green tea extract significantly increased energy expenditure (a measure of metabolism) in adults,
while also boosting fat burning. When men supplemented with 90 mg of EGCG and 50 mg of
caffeine three times daily, their 24-hour energy expenditure increased by 4%. The supplemented
men thus burned 79 more calories a day than men who did not supplement. The increase in
energy expenditure came from burning fat, as opposed to a breakdown of protein (muscle) mass.
These important findings suggest that green tea extract can be an important tool in maintaining
healthy body weight and composition( Dullo et al.1999). Another study lends support to green
tea’s role in healthy weight control in humans. In this trial,
moderately obese adults
supplemented with a green tea extract. After three months, they demonstrated 4.6% decrease in
body weight and a 4.5% decrease in waist circumference. This important study demonstrates
that green tea effectively supports healthy body mass and protects against dangerous excess
weight around the abdomen, which is a potent risk factor for metabolic syndrome (
Chantre and Lairon, 2002).
Review on cardiac
A total of 3,430 men and women aged 30 – 70 years from the Saudi Coronary Artery Disease
Study were examined and 6.3 percent were found to have indications of coronary heart disease
(CHD). The researchers found that those who drank more than six cups of tea per day (>480
mL) had significantly lower prevalence of CHD than non-tea drinkers, even after adjustment for
risk factors such as age and smoking. The researchers also found that drinking six or more cups
of Black Tea per day was associated with decreased serum
cholesterol and triglyceride
concentrations.
• Dutch researchers assessed 4,807 subjects aged 55 years or older without prior history of heart
attack. After a four to seven year follow-up period, the researchers determined that subjects who
drank three or more cups of tea per day (375 mL/day) were 43 percent less likely to develop
myocardial infarction and 70 percent less likely to die from myocardial infarction than non-tea
drinkers (Geleijnse et al.2002).
• A recent meta-analysis discovered that consumption of three cups of
tea per day was
associated with an estimated decrease of 11 percent in the incidence of myocardial infarction
(heart attack);( Peters et al.2001).
• The Zutphen study, which assessed 805 male subjects over a period of five years, found that
the incidence of fatal and nonfatal
first myocardial infarction and mortality from stroke
decreased significantly as intake of flavonoids, derived mainly from tea, increased in a dosedependent manner. A follow-up to this study found that high intake of flavonoids significantly
lowered the risk of stroke in study participants(Keli et al.1996).
Green tea promotes thermogenesis
Earlier research suggested that caffeine in green tea might be responsible for its thermogenic
effect. Later studies, however, reported that green tea’s thermogenic effects were too great to be
attributed to caffeine alone. Instead, scientists proposed that green tea polyphenols may work in
synergy with caffeine to promote thermogenesis ( Dullo et al. 2000). According to recent
findings, EGCG may be an important contributor to green tea’s effects in promoting
thermogenesis and healthy weight control. Scientists believe EGCG works by inhibiting
catechol-O-methyltransferase, an enzyme that degrades norepinephrine. Produced by the adrenal
glands in response to stress, the hormone norepinephrine increases metabolic rate, which likely
contributes to green tea’s effects on thermogenesis ( Sixian et al. 2006).
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