Health Benefits of Green Tea, EGCG and L-Theanine


Green tea, EGCG and l-theanine offer many health benefits for your body and brain. Learn how to get the best results from green tea and its extracts.

tea pot and cup

If you live in a coffee-loving country like the US, you may be surprised to learn that tea is the #1 beverage throughout the world. 

Its consumption equals all other manufactured drinks, including coffee, chocolate, soft drinks, and alcohol, put together. (1)   

But tea is clearly gaining in popularity in the US, since on any given day over 158 million Americans are drinking tea. (2

Green tea is especially renowned for its health benefits. 

It’s been called a “magical elixir” and “one of the healthiest drinks in the world.” (34

All tea comes from the same plant. So what exactly makes the health benefits of green tea better than all other kinds of tea? 

Benefits of Green Tea Over All Others

four types of teaWhite, green, oolong, or black tea comes from the same evergreen bush, Camilla sinensis

The difference in their taste, color, and health benefits comes from the way the tea leaves are processed.

Turning the leaves of the tea plant into the different teas we enjoy involves several steps, with green tea being the least processed. 

Green tea is made from unfermented tea leaves and contains the highest concentration of powerful antioxidants called polyphenols. (5)

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Over 1,400 compounds have been identified in tea. (6)

The health benefits of green tea seem to be mostly due to two widely studied compounds found almost exclusively in green tea — epigallocatechin gallate (EGCG) and l-theanine.

Let’s take an in-depth look at both.

Polyphenols, Catechins, and EGCG in Green Tea

You may come across all three of these terms –polyphenols, catechins, and EGCG — when researching the health benefits of tea. 

Polyphenols are the most abundant antioxidants in the diet. (7)

Antioxidants protect cells from free radical damage — a major cause of disease and aging.

Because green tea is not fermented, it contains 6 times more antioxidants than black tea. (89)

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Polyphenols in tea include catechins, theaflavins, tannins, and flavonoids. (10)

One catechin in particular, epigallocatechin gallate (EGCG), has the interest of researchers since it’s the most bioactive polyphenol in green tea. (11)

EGCG Benefits

EGCG benefits derive from its potent antioxidant and anti-inflammatory properties. (12)

It’s beneficial in treating diseases of all kinds including many kinds of cancer, arthritis, heart disease, inflammatory bowel disease, diabetes, chronic fatigue syndrome, and liver disease. (13)

It also provides many brain benefits including improved learning, memory, and mood.

It can help alleviate anxiety and increase resilience to stress. (14)

EGCG can be extracted and sold separately, but it’s very poorly absorbed when taken as a supplement. (15


L-theanine (sometimes called “theanine”) has been widely studied for its positive effects on the nervous system.

It has the unique ability to increase attention and simultaneously calm you without making you feel drowsy. (16

It works synergistically with caffeine to boost mood, focus and alertness. (17, 18)

L-Theanine Benefits 

Memorial Sloan Kettering Cancer Center lists l-theanine benefits as anti-tumor, anti-obesity, and neuroprotective against stroke and Alzheimer’s. (19)

L-theanine increases levels of the neurotransmitters serotonin, dopamine, and GABA, thus improving recall, learning, and positive mood. (2021)

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It can make you more resilient to stress by reducing both psychological and physiological stress responses. (22)

woman meditating headphonesOne of the more interesting benefits of l-theanine is the effect it has on your brainwave state.

L-theanine causes an increase in alpha activity.

This is a brainwave state associated with relaxation and attention.

It’s very similar to the brainwave state achieved during meditation. (2324)

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Theanine been shown to improve cognition and memory, even in people diagnosed with mild cognitive impairment (MCI). (25)

When taken along with antipsychotic medication, l-theanine can reduce anxiety symptoms of schizophrenia. (26)

It improves sleep quality for those with ADHD. (27)

L-theanine can even help smokers quit smoking. (28)

L-Theanine Side Effects gives l-theanine supplements the thumbs up with no safety concerns despite widespread use and no known drug interactions.

The few adverse reactions reported in studies using tea extracts include headache, dizziness, and GI symptoms. (29)

One warning is that since it can decrease blood pressure, taking it along with high blood pressure medication can cause blood pressure to get too low. (30)

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Talk to your doctor about taking l-theanine if you are undergoing chemotherapy or taking lipid-lowering medicines or sedatives, since l-theanine can alter the effects of these drugs. (31

If you’re going to take an l-theanine supplement, University of Maryland’s Complementary and Alternative Medicine Guide recommends the following dosage: 200 mg 1-3 times daily.

The Many Health Benefits of Green Tea

 Rather three days without food than a day without tea.” — Ancient Chinese Proverb

asian woman drinking teaIn traditional Chinese medicine, tea is considered the most beneficial of all herbs. 

Green tea has been used used to improve digestion, boost physical stamina, stimulate mental clarity and increase longevity.

Nowadays, green tea is said to do everything from preventing cavities to curing cancer.

Let’s take a look at the array of conditions green tea has been proven to help.


The polyphenols found  in green tea protect DNA from oxidative stress and protect telomeres from damage. (32)

Telomeres are endcaps on your chromosomes, similar to the plastic tips of shoelaces. 

Telomere length is currently thought to be the most important indicator of biological age and disease risk. (33, 34)

Brain Benefits of Green Tea

Green tea has so many benefits for your brain that it truly could be called a brain tonic.

It can nourish, stimulate, and protect your brain.

Green tea’s polyphenols, especially EGCG, protect your brain against Alzheimer’s and Parkinson’s. (3536)

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Green tea prevents plaque buildup in the brain and inhibits the activity of enzymes associated with the development of Alzheimer’s. (3738)

Tannins found in green tea may prevent the brain damage that occurs after strokes and other brain injuries. (39

Green tea protects your brain by improving the flexibility of blood vessels, allowing more blood flow, nutrients, and oxygen to reach your brain. (40)

It increases levels of acetylcholine, an important neurotransmitter that can improve memory. (41)

And, of course, all of the brain-boosting benefits of l-theanine that we discussed above — better mood, calm attentiveness, and resilience to stress — can be had by drinking green tea.

cairn lever


Green tea is useful in treating inflammatory diseases, such as arthritis.

It reduces inflammation and slows the breakdown of cartilage, even for those with rheumatoid arthritis. (4243)


The polyphenols in tea, especially green tea, may play an important role in the prevention of cancer. (44)

Countries with the largest consumption of green tea have the lowest cancer rates. (45)

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Compounds in green tea, especially EGCG, stop angiogenesis, the process of blood vessel growth critical to cancer tumors. (46)

Studies show that compounds in green tea specifically inhibit certain types of cancer: bladder, breast, colorectal, esophageal, lung, ovarian, pancreatic, prostate, skin, and stomach. (47)


Green tea has been used traditionally to control high blood sugar. (48)

Regular consumption of green tea increases insulin sensitivity and can lower your risk of developing type 2 diabetes by 33%. (4950)

Green tea can moderate blood sugar spikes when drunk with a high carbohydrate meal. (51)

Heart Health

In a large study of over 40,000 Japanese adults, those who drank the most green tea were significantly less likely to die of heart disease. (52)

Those who drank more than five cups of green tea a day had a 26% lower risk of death from heart attack or stroke than those who drank less than one cup of green tea a day. (53)

Another even larger study found that green tea significantly reduces risk of stroke. (54)

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It lowers total cholesterol and raises HDL (“good”) cholesterol.

Its antioxidant properties can help prevent coronary artery disease. (55)

Weight Loss

tape measure and green pillsWhile green tea may boost metabolism and help burn fat, if you make no other changes to your diet, you should expect your weight loss results to be “modest.” (56)

Some studies have found that drinking green tea can boost your metabolism by about 4%.

Other studies find no increase in metabolic rate. (5758)

An analysis of weight loss studies found in 10 major research databases concluded that there is a small, statistically insignificant weight loss in overweight adults who drank green tea. (59)

Replacing calorific sodas and mocha lattes with green tea might be the best way to lose weight with green tea.

If you swapped one soda every day for a year you’d be ahead by 50,000 calories! 

Green Tea Side Effects and Interactions

Green tea is generally considered safe with almost no known side effects. 

It seems to reduce the absorption of iron from food and drinking it can make anemia worse.

But adding lemon or milk or drinking tea between meals eliminates this problem. (6061)

Drinking green tea temporarily increases pressure inside the eye of glaucoma patients. (62)

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If you are pregnant or breastfeeding, it’s advised not to drink more than 2 cups a day. lists only three medications known to cause interactions with green tea — warfarin, dicumarol, and anisindione — all anticoagulants.

The small amount of vitamin K in green tea can interfere with effectiveness of these drugs. (63)

Some medications have either an increase or decrease in activity when combined with green tea. (64, 65)

It’s recommended to consume green tea “with caution” when using the below medications mainly due to the interaction with caffeine. 

  • Acetominpohen
  • Adenosine
  • Antibiotics
  • Antidiabetic drugs
  • Benzodiazepines 
  • Beta-blockers, propranolol, and metoprolol 
  • Blood thinning medications 
  • Chemotherapy 
  • Clozapine (Clozaril) 
  • Ephedrine 
  • Lithium 
  • Monoamine oxidase inhibitors (MAOIs) 
  • Oral contraceptives 
  • Phenylpropanolamine 
  • Quinolone antibiotics 
  • Statins
  • Tagamet

A Word About Caffeine in Green Tea

One of green tea’s selling points is that it contains less caffeine than other caffeinated drinks like coffee and black tea.

But how much less?

Caffeine Informer is my “go to” place to find the caffeine content in just about anything.

Here’s how the caffeine content in 8 ounces of green tea compares to other teas and a few brand name coffees:

  • Green tea — 25 mg
  • Oolong tea — 27 mg
  • White tea — 28 mg
  • Black tea — 42 mg
  • Matcha tea — 70 mg
  • Dunkin Donuts coffee — 102 mg
  • Keurig V-cup  coffee — 100-140 mg
  • Starbucks Grande coffee — 165 mg

A rule of thumb is that green tea contains roughly 1/2 the caffeine of black tea and 1/4 the caffeine in coffee.

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Caffeine Pros and Cons

exhausted woman with coffee cupCaffeine is a psychoactive stimulant that temporarily increases alertness and the ability to concentrate.

But it does this at a cost.

Caffeine gives its boost by increasing stress hormone output. (66)

Too much caffeine can lead to headaches, irritability, and anxiety, and withdrawal symptoms since it is an addictive substance. (67)

Caffeine often disrupts sleep. It can linger in your system for up to 14 hours.

So the caffeine you drink at lunch really can keep you up at night. (6869)

Green tea’s smaller amount of caffeine along with the presence of calming l-theanine assures that you won’t get wired. 

For anyone looking to cut back on coffee, black tea, or caffeine-laden soda, green tea provides an excellent healthy alternative.

Green tea contains two other alkaloids besides caffeine, theobromine  and theophylline, that work together to provide green tea’s mild stimulant effects. (70)

What About Decaf Green Tea?

A lot of people who want to reduce their caffeine intake use decaffeinated green tea.

But does caffeine-free mean a reduction in the other active components of green tea?

Dr. Iman Hakim is an authority on the health benefits of tea. (71

She says that, depending on the brand, polyphenols could be reduced by 15-25% when green tea is decaffeinated. 

Matcha — Green Tea on Steroids

Matcha green tea is a finely milled powder made from tea leaves grown in the shade in Japan and China. 

Since you are consuming the entire tea leaf instead of making an infusion, matcha is like green tea on steroids.

matcha green tea powderMatcha’s benefits are similar to those of green tea, but even more so.

Matcha contains more potent catechins and antioxidants.

One study found matcha had up to 137 times more EGCG than the other green teas tested. (72)

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Matcha green tea powder might be able to help you lose weight. 

The EGCG found in matcha can reduce food appetite and food intake. (73

Matcha is usually whisked into hot water to make tea, but this powder’s uses are limited only by your imagination.

It can be added to smoothies, soups, sauces, and vegetable purees.

Some of the more creative uses I’ve seen include matcha ice cream, popsicles, and green cupcakes.

With all of these great matcha tea benefits, why isn’t everyone drinking the stuff?

The problem is that even green tea lovers don’t always love matcha’s taste.

It’s been compared to spinach, algae, seaweed, fish, and grass.  😐 

If you want to give it a try, I suggest checking out customer reviews on Amazon to see what others are saying about the taste of a particular brand before you buy it.

Green Tea Extract “Benefits”?

Not everyone is enamored of green tea’s taste.

Taking a green tea extract or supplement may seem like the logical solution.

green tea capsulesGreen tea extract is very popular; in fact, it’s the 4th most commonly used supplement.

While it’s used to help control diabetes, heart disease, and cancer, the main reason it flies off the shelves is its use as a weight loss supplement.

There are few green tea extract benefits over drinking tea.

But there are a few major side effects you should know about.

Green Tea Extract Side Effects

The EGCG in green tea extract or supplements is very poorly absorbed . (74

It’s easy to get too much caffeine when using an extract.

Too much extract can possibly cause DNA damage. (75)

There’s concern that the use of green tea extracts on an empty stomach might produce seriously adverse side effects. 

I was horrified to learn that green extract given to dogs on an empty stomach is fatal. (76)

There are a growing number of case reports in which concentrated green tea extract caused liver damage. (77)

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In most cases, the liver problems disappeared when the extract was discontinued.

But in a few cases permanent liver failure ensued. (78)

The National Institutes of Health warns to not take green tea extract if you are taking any medications that can harm the liver.

This can include over-the-counter remedies like Tylenol (acetaminophen). (79)

One point to consider is that most scientific studies focus on the health benefits of green tea as a beverage, not as green tea supplements.

Supplements aren’t tested for safety and the content of some products may differ from what is specified on the product label. (80)

Green Tea Supplement Dosage

Green tea supplements are usually dried leaves in capsules or liquid extracts. 

Depending on the brand, 100-750 mg per day of standardized green tea extract is the recommended dosage.

It’s easy to get too much caffeine from supplements, so look for caffeine-free versions. 

Hot or Cold? 

Green tea is traditionally brewed in hot water. 

glass and pitcher of teaBut there might be a better way.

Cold-brewed green tea has less caffeine and many people think it tastes better, less bitter and astringent.

Surprisingly cold-brewed tea may actually deliver more health benefits than hot-brewed, since none of the beneficial compounds are destroyed by heat. (81)

Here’s how to make perfect cold-brewed green tea:

Place 4 green tea bags (plain or flavored) into a quart container and fill with cold, filtered water.

Let it steep for 3-4 hours in the refrigerator.

Remove the bags and drink cold, or reheat to drink hot.

I imagine you could also do this with loose tea, but I haven’t tried this. 

Things to Consider When Choosing Green Tea

You can spend as little or as much as you want on green tea.

You can buy it loose, in tea bags, or pre-made in bottles.

The amount of active ingredients in green tea varies wildly depending on the quality of the raw ingredients and how it was brewed.

Tea tends to take up lead from the soil. (82

It’s best to avoid tea from China where industrial pollution is a big problem.

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Interestingly, the decaf process tends to remove lead. (83)

Tea also tends to accumulate fluoride.

Fluoride content in general goes hand-in-hand with overall brand quality with lower quality brands containing excessive amounts of fluoride. (84)

Freshly brewed loose tea extracts more nutrients and flavor than using tea bags. (85)

Tea bags are usually bleached with unsavory chemicals.

Those little plastic mesh bags are suspected of being toxic especially when subjected to boiling water. (86)

You need to drink about 3 cups per day to get any real health benefits. (87)

A cup of tea as is usually considered a 6-ounce serving, not a typical 8-ounce cup.

If you are buying pre-made green tea in a bottle you almost certainly are spending a lot per serving and getting very little health benefits in return.

green tea and cherry pieA consumer study found that the EGCG level in Diet Snapple Green Tea was negligible. 

No surprise there. Snapple is not a health drink. 

But more surprising was that Honest Tea Green Tea with Honey contains only about 60% of the catechins claimed on the label. (88)

One popular brand of bottled green tea contains 240 calories and 61 grams of sugar, more sugar than 4 slices of cherry pie! 

Somewhat surprising was that Lipton Green Tea bags were the most cost-effective way to get your EGCG due to their low cost (10 cents per bag) and relatively high level of EGCG (71 mg per serving). (89)

If you want to get the health benefits of green tea covered in this article here’s what you really need to know …

Skip green tea supplements.

Drink three 6-ounce servings of green tea per day.

Loose tea is best.

When choosing tea, quality matters. 

It’s that simple.

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