In 1211 the Japanese monk Eisai wrote:
Tea is a miraculous medicine for the maintenance of health. Tea has an extraordinary power to prolong life. Anywhere a person cultivates tea, long life will follow. In ancient and modern times, tea is the elixir that creates the mountain dwelling immortal. 
Drinking tea not only provides us with an enjoyable taste experience and a means of relaxation. Today, scientific research has confirmed what those in the East believed for many years – that the tea leaf does have wide-ranging health benefits.
Over the past several decades, thousands of studies have been published that have identified and quantified thousands of bioactive compounds in the leaves of the Camellia sinensis plant that are used to make green, black, white and oolong tea. Some studies have been conducted that reveal the mechanisms of actions by which specific tea compounds may elicit health benefits and show how these diverse elements in tea work synergistically to promote health when consumed as a plant-based beverage.
The extensive tea research includes laboratory, animal studies, observational studies of large populations and randomised clinical trials. The benefits of tea are often attributed to the phenolic compounds (some of which act as antioxidants). Numerous studies with the major catechins in tea, namely epicatechins in green tea and the theaflavins and thearubinigins in black tea, show that these compounds are at least partially digested, create many bioactive metabolites and sometimes pass through the body intact whereby they provide health benefits.
The most recent research suggests that consuming tea as it was intended- as a beverage- was the best way to help ensure tea would impart the most health benefits. Supplements of specific catechins may have a particular benefit but lack the total spectrum of advantages that the beverage contains. Hundreds of thousands of bioactive elements are found within tea’s leaves and together, and it is likely that they work synergistically to impact virtually every cell in the human body- from the heart, bones, brain, skin, and gastrointestinal tract.
Some potential health benefits of drinking tea are summarised below:
1. Antioxidant Protection
Tea contains an abundant source of natural plant-derived antioxidant compounds called polyphenols. In this broad polyphenol class of antioxidants are flavanoids and catechins, which have been shown in many studies to provide protective antioxidant action against harmful free radicals that can damage DNA, cell membranes and other cell components.
While most fruits and vegetables contain natural antioxidants that help combat free radicals, it is the tea leaf that boasts one of the highest total flavanoid contents of all plants – at 15% of its dry weight. 
Green tea and white tea are believed to have higher antioxidant levels than both oolong and black tea, due to their differing manufacturing processes.
2. General Nutrition
Tea taken on its own without milk, sugar or honey has no calories and a significant level of certain micronutrients.
Consuming four cups of tea a day can provide one with-:
- approximately 17% of the recommended daily intake of calcium
- 5% for zinc
- 22% for vitamin B2
- 5% for folic acid
- 5% for vitamin B1 and B6It also contains trace amounts of manganese and potassium 
3. Cancer Treatment & Prevention
There are many studies that have indicated that green tea may help protect against a range of cancers (including prostate, lung, bowel and breast cancer). This has been found to be largely due to tea’s high antioxidant protection. In recent research, it is the catechins in tea, the most abundant of which is epigallocatechin gallate (EGCG) that has been found to play a role in protecting against degenerative diseases by scavenging reactive oxygen and nitrogen species and inhibiting pro-oxidant enzymes and inducing antioxidant enzymes- all important processes in the protection against cancer. Furthermore, oxidative stress has been found to generate DNA damage, and alter expression of genes involved in cell cycle regulation and angiogenesis. Therefore, the antioxidant actions of green tea may prove to be beneficial in preventing the cell mutations seen in tumour development.
Green Tea and Conventional Cancer Treatment
EGCG (epigallocatechin gallate)- an antioxidant from Green tea has also been trialled alongside conventional chemotherapy and radiotherapy treatments and has proven to be safe for concurrent use- having actions to actually enhance the treatment efficacy and decrease side effects. Firstly, in a chemo-resistant animal model of hepatocellular carcinoma, EGCG from green tea was found to significantly enhance the effect that doxorubicin (a chemotherapy drug) had upon cellular proliferation. Furthermore, the administration of EGCG was found to markedly increase intracellular concentration of doxorubicin, implying that EGCG inhibits P-glycoprotein (P-gp) activity. P-glycoprotein is an important protein of the cell membrane that pumps many foreign substances out of cells, such as chemotherapy drugs. It was concluded that green tea may augment doxorubicin treatment by increasing its effects and enhancing cellular accumulation.  Secondly, in another study, EGCG was also trialled in tamoxifen-resistant breast cancer cell lines. It was noted to decrease P-gp gene expression that correlated with a 47% reduction in P-gp activity. EGCG was also noted to decrease Breast Cancer Resistance Protein (BCRP), a specific ABC transport protein seen in breast cancer cells.  Furthermore, EGCG was also found to inhibit cancer cell growth and demonstrated dose-dependent apoptosis- the process of programmed cell death (PCD). Biochemical events lead to characteristic cell changes (morphology) and death. It was concluded that the ability of EGCG to effect two multi-drug resistant mechanisms as well as anti-cancer actions gives good reason for use in cases of chemotherapy resistance. 
4. Cardiovascular Support
While free radicals are a major cause of heart disease, tea that contains a high level of antioxidants that fight free radicals may help to inhibit the development of heart disease and reduce the risk of heart attack and stroke. Many studies have shown that both green tea and black tea consumption help to support the cardiovascular system in various ways. The flavonoids in tea have been found to improve the endothelial function of blood vessels. In vitro studies provided evidence for direct effects of flavonoids from tea on endothelium, resulting in vasorelaxation. These effects can help to improve the overall functionality of blood vessels and reduce hypertension.
An inverse relationship has also been found between flavonoid intake and cardiovascular disease in different epidemiological surveys and there has also been a few case-control or clinical trials completed supporting this. One such study has been conducted by Claudio Ferri MD and it found in 19 normotensive and 19 hypertensive individuals that black tea was able to reduce blood pressure. In the hypertensive patients, black tea appeared to counteract the negative effects of a high-fat meal on blood pressure and arterial blood flow. Hypertensive subjects were instructed to drink a cup of tea after a meal that contained .45 grams fat/lb. body weight. The results suggest that tea prevented the reduction in flow-mediated dilation (FMD), the arterial ability to increase blood flow that occurs after a high-fat meal. In a previous study conducted by Ferri, tea improved FMD from 7.8 to 10.3%, and reduced both systolic and diastolic blood pressure by -2.6 and -2.2 mmHg, respectively, in study participants.
Dr. Ferri concluded the following-:
Our studies build on previous work to clearly show that drinking as little as one cup of tea per day supports healthy arterial function and blood pressure. These results suggest that on a population scale, drinking tea could help reduce significantly the incidence of stroke, heart attack and other cardiovascular diseases.
5. Increasing Mental Alertness and Reducing Anxiety and Stress
The amino acid L-theanine, which is found in the tea plant, has been known to have a profound effect on the nervous system. Theanine is absorbed by the small intestine and crosses the blood-brain barrier where it influences the “feel-good” neurotransmitters of the brain (serotonin and dopamine). This in turn increases the alpha brain-wave activity and has been found to have the effect of producing a calmer, yet more alert, state of mind.
To test whether L-theanine significantly increases brain activity in the alpha frequency band (indicating that it relaxes the mind without inducing drowsiness), Nobre et al conducted a study in 2008. Electroencephalograph (EEG) was measured in healthy, young participants at baseline and 45, 60, 75, 90 and 105 minutes after ingestion of 50mg L-theanine (n=16) or placebo (n=19). Participants were resting with their eyes closed during EEG recording. There was a greater increase in alpha activity across time in the L-theanine condition (relative to placebo (p+0.05). Furthermore, while alpha activity is known to play an important role in critical aspects of attention, the conclusion was that L-theanine, at realistic dietary levels, has a significant effect on the general state of mental alertness and arousal, whilst also keeping the nervous system calm and relaxed.
Additionally, L-theanine is known to block the binding of L-glutamic acid to glutamate receptors in the brain, and has been considered to cause anti-stress effects by inhibiting cortical neuron excitation. In a study by Yokogoshi et al, the effects of orally administered L-theanine or caffeine on mental task performance and physiological activities under conditions of physical or psychological stress in humans was measured. Fourteen participants each underwent three separate trials, in which they orally took either L-theanine + placebo, caffeine + placebo, or placebo only. The results after the mental tasks showed that L-theanine significantly inhibited the blood-pressure increases in a high-response group, which consisted of participants whose blood pressure increased more than average by a performance of a mental task after placebo intake. Caffeine tended to have a similar but smaller inhibition of the blood-pressure increases caused by the mental tasks. The result of the Profile of Mood States after the mental tasks also showed that L-theanine reduced the Tension-Anxiety scores as compared with placebo intake. The findings above denote that L-theanine not only reduces anxiety but also attenuates the blood-pressure increase in high-stress-response adults.
6. Weight Loss
Green Tea & Weight Loss
Many research studies have shown that drinking green tea helps us to shed unwanted kilos by helping to firstly increase our metabolism (burn more calories/kilojoules throughout the day), and secondly to increase our body's ability to burn fat (fat oxidation). While some of green tea's effect on our metabolism is known to come from the caffeine it contains, it isn't just due to this. It is rich in catechins (including Epigallocatechin gallate or EGCG) that enhances antioxidant defences and assists detoxification to help maintain normal health of the skin, digestive tract and liver. In combination with a calorie controlled diet and regular exercise, green tea can assist in the management of weight loss as has been found in many research studies.
Green Tea & Weight Loss Research Summary-:
Green tea has been so widely researched for its health benefits, particularly its ability to help with weight loss.
I have listed a summary of some research supporting this below-:
* Green Tea and Weight Loss: A 12-week randomised controlled trial with 60 obese adults was performed in a hospital setting with all 60 participants placed on a diet that included three meals per day. All the food was prepared for the participants. Half the group received green tea. Those in the green tea group lost significantly more weight—24 pounds—over the 12 week period. The researchers demonstrated that weight loss occurred by green tea increasing energy expenditure and fat oxidation.
* Green Tea and Weight Loss in Obese Individuals: Another 12-week randomised controlled trial with green tea and obese adults produced little weight loss (less than 1 pound). There was no dietary intervention and the dose of green tea catechins was relatively low (458 mg per day). However, even this modest intake of green tea catechins did produce statistically significant reduction in LDL cholesterol and triglycerides while raising the protective HDL Cholesterol, and adiponectin , which prevents insulin resistance. Even though weight was not improved on this dose of green tea it did produce a variety of important metabolic changes that are associated with reduced risk for diabetes and heart disease.
* Green Tea Effect on Body Composition: In a randomised placebo controlled trial moderately overweight adults consumed 1,900 mgs of green tea catechins per day for 90 days. The green tea also contained 400 mg of caffeine. At the end of the study the people in the green tea group lost 2.64 pounds on average, and ¾ inch from their waistline and also reduced body mass index—not bad considering that no dietary or exercise changes were part of the study.
* Green Tea Helps Blood Sugar Control in Type 11 Diabetes: Consumption of 582 mg of green tea catechins per day for 12 weeks in type 2 diabetic patients compared to a control group of diabetic patients, enabled a statistically significant reduction in their waistline (abdominal fat). Importantly, green tea catechins promoted a restored insulin production by the pancreas. Catechins caused a significant increase in adiponectin, the important hormone signal coming from fat that improves insulin resistance. The combination of diabetic medication and green tea produced a statistically significant reduction in hemoglobin A1C. These results indicate that even modest intake of green tea catechins improves blood sugar control in type 2 diabetic patients. When blood sugar control is being improved in conjunction with a trend of weight loss, health is being restored.
* Green Tea and Other Antioxidants Assist Metabolic Profile: A study published in 2010 in the American Journal of Nutrition showed that a combination of green tea, resveratrol, vitamin E, vitamin C, omega-3 fatty acids, and tomato extract given to overweight men for five weeks raised their adiponectin level by seven percent. The researchers documented numerous favorable metabolic changes indicating: modulated inflammation within white adipose tissue, improved endothelial function of arteries, improved antioxidant function, and increased fat burning by the liver.
* Green Tea Inibits the Accumulation of fat in Cells: In a transgenic mouse study, it was found that green tea in combination with exercise extended the mouse’s health and life. The green tea enabled better use of oxygen by muscles, improved antioxidant function within muscles, and increased the rate of fat burning by muscles.
* Green Tea Reduces Obesity Associated Inflammation: It is well-known that being overweight or obese is associated with increased inflammation, both within white adipose tissue and around your body. One way to help calm inflammation is through the function of specialised regulatory T cells hat initiate signals that are anti-inflammatory. A recent study in the British Journal of Nutrition found that obese humans have fewer of these important regulatory T cells than normal weight people and the T cells they did have were less active in terms of quenching inflammation. The researchers went on to expose the regulatory T cells of the obese people to ECGC and found that the T cells woke up and started producing anti-inflammatory signals and were then able to cause the reduction in NF-kappaB, the primary inflammatory gene signal. Researchers also showed that ECGC increased anti-inflammatory activation in the regulatory T cells of the normal weight people in their study.
* Green Tea can Help Obese Children: Consumption of 576 mg green tea catechins per day for 24 weeks in obese children found that those who were the most obese had a statistically significant reduction in waist circumference, blood pressure, and LDL cholesterol.
* Green Tea Boosts Adinopectin Production by Fat Cells: Further insights into the molecular mechanisms of green tea come from a variety of recent animal and cell studies. Studies with fat cells show that green tea catechins turn on gene signals that produce adinopectin. Adequate adiponectin production is required to prevent insulin resistance and type 2 diabetes. In one study, green tea has been shown to blunt the effect of insulin on baby fat cells, helping prevent them from turning into mature fat storing fat cells.
* Green Tea Inhibits the Production of New Fat Cell: Leptin is the primary hormone coming from white adipose tissue that regulates weight gain. Too much leptin in the blood causes leptin resistance, a problem that sets into motion poor metabolic health. A recent animal study showed that green tea decreased total cholesterol, LDL cholesterol, and triglycerides while also lowering the levels of leptin in the blood. Transgenic mice—mice that make no leptin—(ob/ob) experience unrelenting appetite, obesity, and fat accumulation in all the wrong places, such as the liver. In this extreme model of malfunction green tea was able to prevent at from accumulating in the liver. This finding is significant since fat accumulation in the human liver is a key marker that metabolic health is in big trouble.
* Green Tea Helps Bone Health: A recent study also showed green tea helped build bone. Green tea catechins significantly boosted the activity of bone building cells known as osteoblasts while reducing the activity of the osteoclasts that take down bone. A significant reduction of the primary inflammatory gene signal, NF-kappaB , was associated with these positive findings. Not only is this good news as yet another bone helping nutrient, but new developments are indicating that positive bone health and proper metabolism are highly linked.
 Okakura, K., The Art of Tea, page 11
 U.S. Department of Agriculture, USDA Database for the Flavanoid Content of Selected Foods, Release 2.1, January 2007
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 Claudio Ferri, MD, University L’Aquila, Italy, at the 5th International Symposium on Tea and Health in 2012.
 Claudio Ferri, MD, University L’Aquila, Italy, at the 5th International Symposium on Tea and Health in 2012.
 Claudio Ferri, MD, University L’Aquila, Italy, at the 5th International Symposium on Tea and Health in 2012
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