It originated more than 4,000 years ago and was a pivotal part of Chinese and Japanese culture. Scholars wrote about it. Emperors savored it. Zen monks obsessed over it.
For millennia, it was an indispensable ingredient in traditional medicines and alternative remedies. And today you can buy it in coffee shop chains, in grocery stores and in outdoor markets. You can even get it in supplement form.
In fact, it is the second most consumed beverage on the planet, after water. And with its mild flavor and soul-warming scent, it’s not hard to see why this beverage is so popular.
We are, of course, talking about green tea.
What is Green Tea?
Modern science is still trying to get their arms around the amazing health benefits of green tea. But what exactly is green tea?
Technically, black and green teas are the same, as they both come from the same tea plant, Camellia sinensis. However, the way the leaves are treated after harvest determines their classification.
If the leaves are crushed and allowed to naturally ferment (or oxidize), a process that darkens the leaves, then you have black tea. Conversely, if the leaves are heated, the natural plant enzymes are inactivated, blocking oxidation, and the leaves hold their green color—hence green tea.
But color isn’t the only difference. Freshly harvested Camellia sinensis tea leaves contain polyphenols, special chemicals that have exceptional antioxidant activity and help promote overall good health and well-being.
Turns out, the oxidation that occurs during black tea processing robs the plant of much of its polyphenols and therefore also many of the health benefits they convey. Meanwhile, the heating that occurs when producing green tea blocks the oxidation process, which ironically allows the polyphenols to remain intact. Seems like it would be the other way around, doesn’t it?
The major polyphenols are primarily flavonoids and include:
- Catechins, which are also found in chocolate.
- Proanthocyanidins, which are found in apples, grape seed and red wine.
- Epigallocatechin gallate, which is abbreviated and commonly referred to as EGCG.
Of these, EGCG is the most widely associated with green tea, and is the key nutrient that gives this delightful beverage its health advantages. Specifically, proponents of green tea claim it can prevent America’s most feared health conditions: cancer, heart disease and obesity.
Conditions Supported by Green Tea
- Blood sugar
- Brain health
- Digestive health
- Heart health
- Immune health
- Weight loss/maintenance
What Does the Research Say?
In a study published in February 2013, scientists reported that green tea extract improves blood sugar metabolism in diabetic rats.1
Scientists evaluated the impact of green tea in healthy and diabetic rats. The rats received 300 mg/kg body weight of green tea extract daily for 30 days. The researchers evaluated blood glucose, insulin, hemoglobin and hemoglobin A1c, which measures long-term blood sugar control. The investigators also assessed key enzymes of carbohydrate metabolism including hexokinase, pyruvate kinase, lactate dehydrogenase, glucose-6-phosphatase, fructose-1,6-bisphosphatase, glucose-6-phosphate dehydrogenase, glycogen synthase and glycogen phosphorylase.
The investigators found that green tea supplementation in diabetic rats resulted in significantly reduced levels of plasma glucose and hemoglobin A1c and increased levels of insulin and hemoglobin. Additionally, the researchers showed that alterations in the carbohydrate metabolism enzymes seen in diabetic rats were reverted to near normal levels by the supplementation with green tea extract. The investigators also determined that green tea supplementation to the diabetic rats improved muscle and hepatic glycogen content, suggesting the anti-hyperglycemic potential of green tea extract.
The scientists stated, “This study indicates that the administration of green tea extract to diabetic rats resulted in alterations in the metabolism of glucose with subsequent reduction in plasma glucose levels.”
A second study, this one from Japan and published in 2014, indicates that drinking green tea has beneficial effects on postprandial (post-meal) glucose levels in postmenopausal women.2 Blood sugar levels normally rise slightly after eating. This causes the pancreas to release insulin to move glucose from the blood and store it for energy.
Postprandial glucose tests measure blood sugar levels two hours after the start of a meal. By this point, glucose levels in healthy people should fall back to normal. However, in people with diabetes, glucose levels often remain high. Moreover, elevated postprandial blood sugar in non-diabetics can increase the risk of developing type 2 diabetes.
In this study, researchers examined the effects of drinking green tea on postprandial blood sugar and oxidative stress in healthy postmenopausal women. For this four-week study, 22 participants were evenly divided and placed into either a green tea or placebo group. At baseline and after four weeks, all the volunteers drank their designated beverages with breakfast and at lunch, three hours after breakfast. Blood samples were drawn in fasting state as well as at two, four and six hours after breakfast.
Results showed that “postprandial glucose concentrations were three percent lower in the green tea group than in the placebo group… Conversely, serum postprandial thioredoxin concentrations were five percent higher in the green tea group than in the placebo group.”
This second point is important, as thioredoxin is a class of proteins that act like antioxidants. It is found in all living organisms and plays an important role in many biological processes.
The American Journal of Clinical Nutrition published one of the first studies to support green tea’s role in memory maintenance back in 2006. Researchers compared the green tea intake and cognitive function of over 1,000 elderly Japanese subjects. And they found that drinking just a couple of cups of green tea daily cuts rates of cognitive impairment by more than half.3
Two or more cups seemed to deliver the most benefit. But even if you drank four to six cups a week—just a cup every other day or so—these results suggest that you’d still enjoy a 38 percent lower risk of mental decline.
So what’s the secret behind green tea’s superior memory protection? Well, there’s EGCG, for starters. In addition to being a powerful antioxidant, studies show that this green tea catechin boosts neuron generation, which enhances memory centers in the brain.4
But that’s not all. Another clinical study published in April 2014 showed that green tea extract also improves connectivity between your brain’s neural networks, especially where working memory is concerned.5
According to a study published in the Journal of the National Cancer Institute, drinking green tea reduced the risk for esophageal cancer by 57 percent for men and 60 percent for women.6
Similarly, a meta-analysis from Carcinogenesis looked at four previously published studies on green tea.7 They found that an approximately 20 percent statistically significant reduction for breast cancer in those people who had a high green tea intake—at least twice a week for more than three months.
According to a study published in March 2013, green tea and coffee intake decreases the risk of depression.8 The subjects included 537 adults between 20-68 years of age. The subjects completed a dietary questionnaire to evaluate green tea and coffee intake, and researchers calculated the caffeine intake from the data collected. The researchers assessed depression symptoms using the Center for Epidemiologic Studies Depression Scale.
The investigators found that intake coffee or green tea was associated with a lower likelihood of depressive symptoms. More specifically, the subjects who drank four or more cups of green tea per day had a 51 percent decreased in the likelihood of having depressive symptoms compared to the subjects who drank one cup of green tea or less per day.
Additionally, the subjects who drank two or more cups of coffee per day had a 39 percent decrease in the likelihood of developing depressive symptoms compared to the subjects who drank less than one cup of coffee per day. Furthermore, the researchers determined that the subjects with the highest caffeine consumption had a 43 percent decrease in the likelihood of having depressive symptoms compared to the subjects with the lowest caffeine intake.
The investigators concluded, “Results suggest that higher consumption of green tea, coffee and caffeine may confer protection against depression.”
According to a double-blinded, placebo-controlled pilot study published in August 2013, epigallocatechin-3-gallate (EGCG), a constituent of green tea, improves symptoms in individuals with refractory ulcerative colitis.9
Twenty subjects with mild to moderate ulcerative colitis received 400 mg of total EGCG (Polyphenon E) daily, 800 mg of total EGCG daily or a placebo for 56 days. The investigators evaluated the subjects at the beginning of the study and again after the intervention period using the ulcerative colitis disease activity index and the inflammatory bowel disease questionnaire.
The researchers determined that 66.7 percent of the subjects who received EGCG responded to treatment compared to no patients in the placebo group. Additionally, the investigators showed that 53.3 percent of the subjects achieved remission in the EGCG group compared to no subjects in the placebo group.
The researchers concluded, “This agent [EGCG] holds promise as a novel option for the treatment of patients with ulcerative colitis with mild to moderately active disease.”
Another area where green tea really shines is cardiovascular health. Japanese researchers from Tohoku University School of Medicine spent 11 years studying the relationship between green tea consumption and death from all causes.10
After 11 years of tracking the participants and tabulating everything they ate and drank, as well as their history of disease and current health habits, researchers found that consumption of green tea is associated with reduced mortality due to ALL causes, and specifically showed reduced mortality due to cardiovascular disease.
This was also seen in a double-blind, placebo-controlled trial published in June 2012, which found that green tea extract alters insulin resistance and cardiovascular risk factors in obese, hypertensive subjects.11
The subjects included 56 obese individuals with hypertension. The subjects received 379 mg of green tea extract or placebo daily for three months. The researchers assessed the subjects for key measures, including blood pressure, plasma lipid and glucose levels, creatinine levels for kidney function and insulin levels and insulin resistance at the beginning of the study and again after three months of supplementation. The investigators also evaluated levels of the inflammatory markers tumor necrosis factor-alpha and C-reactive protein (CRP), as well as total antioxidant status.
The researchers found that, after three months of supplementation with green tea extract, both systolic and diastolic blood pressure significantly decreased in the green tea group, as compared to the placebo group. In addition, fasting serum glucose, insulin levels and insulin resistance also decreased in the green tea extract group compared to the placebo group.
The green tea extract group also had significantly lower levels of the inflammatory markers tumor necrosis factor-alpha and CRP and higher total antioxidant status. Furthermore, the researchers showed that the subjects in the green tea extract group had reductions in total and low-density lipoprotein (LDL) cholesterol and triglycerides, and increased high-density lipoprotein (HDL) cholesterol.
The study authors stated, “In conclusion, daily supplementation with 379 mg of green tea extract favorably influences blood pressure, insulin resistance, inflammation and oxidative stress, and lipid profile in patients with obesity-related hypertension.”
Green tea also appears to reduce the risk of stroke. In fact, a study published in March 2013 found that higher green tea and coffee intake decreased the risk of cardiovascular disease and stroke.12
The subjects included 82,369 adults between 45-74 years of age without cardiovascular disease or cancer at the beginning of the study. The subjects completed food-frequency questionnaires at the beginning of the study to assess coffee and green tea intake. The researchers followed the subjects for 13 years to evaluate the incidence of strokes and coronary heart disease.
The investigators determined there were 3,425 cases of stroke and 910 cases of coronary heart disease during the follow-up period. The researchers showed that green tea intake of two to three cups per day reduced the risk of stroke by 14 percent and four cups or more per day reduced the risk of stroke by 20 percent compared to the subjects that rarely drank green tea. Additionally, higher intake of green tea was associated with decreased risk of cardiovascular disease and stroke subtypes.
The investigators also found that the subjects that drank coffee three to six times per week reduced the risk of stroke by 11 percent compared with the subjects that rarely drank coffee. Similarly, the subjects that drank coffee once per day showed a 20 percent decrease in the risk of stroke and those that drank coffee two or more times per day showed a 19 percent decrease in the risk of stroke compared to the subjects that rarely drank coffee. Higher coffee intake was associated with a decreased risk of cardiovascular disease and cerebral infarction.
The investigators concluded, “Higher green tea and coffee consumption were inversely associated with risk of cardiovascular disease and stroke in general population.”
In 2010, research published in Cancer Prevention Research demonstrated that mice that consumed green tea had more protection against the harmful effects of ultraviolet radiation. Laboratory tests showed that this was likely because green tea boosted the DNA repair process in these animals and improved responses in the immune system.
Another study, this one published in the Journal of Nutrition in 2008, found that green tea’s effects on the immune system may also help people manage rheumatoid arthritis.
Similarly, in September 2012, researchers reported that EGCG suppressed the production of reactive oxygen species induced by the influenza-A virus and eased the development of pneumonia in experimental models.13
Researchers exposed cells to influenza-A followed by EGCG to evaluate the production of reactive oxygen species, a key contributor to free radicals. The investigators also treated mice with EGCG for five days, with exposure to influenza-A on the third day. Other mice were treated with oseltamivir, an antiviral drug, prior to exposure to the influenza virus for comparison. The researchers assessed the mice for viral titers and development of pneumonia in the lungs.
The investigators found that administration of EGCG to the cells after influenza-A infection reduced the production of reactive oxygen species. In the mice, the scientists determined that oral administration of EGCG prior to influenza-A infection resulted in dramatically improved survival rate, decreased the average number of viral infections and eased viral pneumonia in the lungs. These findings were equivalent to the mice treated with the antiviral drug.
The researchers concluded, “The results provide a molecular basis for development of EGCG as a novel and safe chemopreventive agent for influenza A infection.”
Where green tea seems to really shine (or at least where it gets a lot of attention) is weight loss. In fact, a meta-analysis of 15 studies—a total of nearly 1,230 participants—published in 2010 found that caffeinated green tea significantly lowered body mass index, body weight and waist circumference, as compared to caffeine alone.14
Other studies show that green tea helps to reduce fat. In one study collaboration between researchers from Peking University, the Chinese Center for Disease Control and Prevention and Japan’s Kao Corporation, researchers analyzed the effects of catechins from green tea on visceral (abdominal) fat reduction.15
In the randomized, double-blind, placebo-controlled 12-week trial published in January 2012 in the Journal of Functional Foods, researchers evaluated the effects of green tea catechins in 118 obese men and women, ranging in age from 20- to 65-years-old.
Test group participants were asked to consume one 350 ml drink of green tea fortified with 609.3 mg of catechins as well as 68.7 mg of caffeine per bottle every day, while control group participants received the unfortified drink. The subjects consumed the drinks no more than 30 minutes following lunch. The researchers also asked all participants to keep a diary of both their diet and exercise.
The study authors measured abdominal fat, body weight and composition of each participant at the beginning of the study (week 0), week eight and following the completion of the trial (week 12).
Following week 12, those who consumed the catechin/caffeine fortified drink saw an average 9.5 cm2 reduction in visceral fat area, a signficant change compared to the control group.
As part of its weight loss benefits, green tea consumption also helps to improve other areas of health related to obesity, namely bone health and lipid levels. For example, a study published in June 2012 indicates that the polyphenols from green tea influence body composition and bone density in obese rats.16
The researchers fed 36 three-month-old female rats a low-fat or a high-fat diet for four months. Next, the rats fed the low-fat diet were continued on that diet for an additional four months, and the investigators supplemented half of the rats fed the high-fat diet with green tea polyphenols in their drinking water for the following four months.
The researchers assessed the rats for body composition, femur bone mass and strength, and serum levels of obesity-related endocrine hormones including insulin-like growth factor-I, leptin and adiponectin. The scientists also measured pro-inflammatory cytokines and liver glutathione peroxidase protein expression (a measure of oxidation).
The researchers showed that, after eight months, the rats fed the high-fat diet had increased percentage of fat mass and reduced percentage of fat-free mass, increased serum insulin-like growth factor-I and leptin levels and reduced bone strength and glutathione peroxidase protein expression compared to the rats fed the low-fat diet.
The investigators found that supplementation of green tea polyphenol to the obese rats resulted in increased percentage of fat-free mass, bone mineral density and strength and glutathione peroxidase protein expression. They also demonstrated that green tea polyphenol supplementation reduced the percentage of fat mass, serum insulin-like growth factor-I, leptin, adiponectin and pro-inflammatory cytokines.
The scientists stated. “This study shows that green tea polyphenol supplementation benefited body composition and bone properties in obese rats possibly through enhancing antioxidant capacity and suppressing inflammation.”
Similarly, a study published in May 2012 found that green tea reduced lipids, body mass index and glucose, while increasing total antioxidant levels and balancing mineral status in obese subjects.17
In this randomized, double-blind, placebo-controlled trial, researchers assessed the impact of green tea in 46 obese subjects. The subjects received 379 mg of green tea extract or a placebo daily for three months duration. The investigators assessed body mass index, waist circumference, blood pressure, total antioxidant status plasma lipids, glucose, calcium, magnesium, iron, zinc and copper at the beginning of the study and again after three months.
Green tea supplementation for three months decreased body mass index, waist circumference and levels of total cholesterol, low-density lipoprotein (LDL) cholesterol and triglycerides. Green tea supplementation increased total antioxidant status and zinc compared to levels at the beginning of the study.
In addition, investigators found decreased glucose and iron levels and increased high-density lipoprotein (HDL) cholesterol and magnesium with green tea supplementation compared to the placebo group. After three months, the researchers found a positive correlation between iron and body mass index and between magnesium and HDL-cholesterol, and a negative correlation between magnesium and glucose levels.
The study authors stated, “The present findings demonstrate that green tea influences the body’s mineral status. Moreover, the results of this study confirm the beneficial effects of green tea extract supplementation on body mass index, lipid profile and total antioxidant status in patients with obesity.”
How to Use Green Tea
Aim for three 8-ounce cups of green tea a day. That translates to 24 ounces a day. That is enough to provide roughly 240 to 320 mg of polyphenols.
If you prefer not to drink the tea, you can take 300–400 mg daily of green tea extract a day. Just be sure the product is standardized to 80 percent total polyphenol and 55 percent epigallocatechin, providing a minimum of 270 mg of EGCG.
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