Green Tea in Focus: A Dietitian Explains the Benefits and Risks

What Is Green Tea?

Green tea comes from the leaves of the Camellia sinensis plant. This is the same plant that produces white, yellow, black, purple, oolong, and Pu-erh teas, which are considered “true” teas.

The differences between these types of teas are in how they are processed. Varieties of tea undergo different steps that may or may not include withering, drying, fermenting, rolling or cutting, and heating.

Green tea is quickly processed compared to darker teas. After the leaves are plucked, they are quickly dried or steamed, shaped, and sent out for sale.

Tea is traditionally grown in areas like China, India, and Sri Lanka due to the climate, acidic soil, and rainfall needed for tea plants to grow optimally. However, these days, dozens of countries are producing varieties of tea.

Health Benefits of Green Tea

People can experience the benefits of green tea both as a beverage and a concentrated extract.

Here’s what the research says about green tea, its major components, and how it can benefit your health.

Can Support Mental Focus and Calm

Green tea extract, EGCG, and L-theanine have been studied for their abilities in reducing anxiety and psychological stress. Specifically, The compounds found in green tea are able to support cognition, mood, and brain function in the short and long term with daily intake.

A 2017 review examined the effects of green tea on cognition, mood, and brain function. Studies examining green tea, green tea extract, EGCG, L-theanine, and caffeine were included in this review. (1)

Researchers found that these compounds enhanced memory and attention, improved executive function and information processing speed, reduced tension and anxiety, and reduced mental fatigue either alone or in combination with other components of green tea (e.g., L-theanine and caffeine).

Daily doses of L-theanine (200 mg to 600 mg) or intake of between 100 mL to 500 mL (approximately 0.5 to 2 cups) of green tea supported these benefits, though more research needs to be done.

May Reduce Heart Disease Risk

Research suggests that there are several mechanisms thought to support the use of green tea for heart health. The catechins in green tea can reduce your risk of coronary heart disease and stroke due to the activity of its polyphenol antioxidants.

A 2020 study on tea consumption and cardiovascular risk found that Chinese adults who regularly drank green tea had a reduced risk of coronary heart disease and stroke. (2)

In the study, regular tea drinkers were observed to live without cardiovascular disease for longer and had an overall longer life expectancy.

In animal and human studies, polyphenols and catechins in tea can help reduce inflammation, improve the relaxation of the aorta, reduce blood pressure, reduce blood clot formation, and inhibit cholesterol absorption in the body. (3)

May Support Healthy Gut Microbiota

A growing body of research supports green tea for supporting a healthy gut.

As we mentioned previously, catechins are a type of polyphenol antioxidant. Polyphenol compounds like catechins can hinder the activity of harmful bacteria and assist with balancing the gut microbiota.

Polyphenols are considered prebiotics and feed the beneficial bacteria in your gut. When beneficial bacteria are fed, they can reduce the concentration of inflammatory bacteria in the gut and reduce overall gut inflammation. (4)

These bacteria also produce short-chain fatty acids like butyrate and propionate, which are fats that can be used by cells in the gut or body to reduce inflammation, support regular metabolism, and reduce disease risk. (5)

A 2021 review found that green tea could help reduce dysbiosis (imbalances in gut bacteria) induced by cancer and high-fat diets, and may reduce symptoms of Parkinson’s disease previously made worse by dysbiosis. (6)

May Increase Metabolism and Weight Loss

Green tea is not only a low-calorie beverage, but its active compounds may also increase metabolism and decrease fat gain.

While all green tea catechins appear to contribute to metabolic benefits, EGCG is the main catechin that supports metabolism. Caffeine present in green tea can also support fat burning, weight loss, and appetite reduction. (7, 8)

A 2019 review found that green tea can increase thermogenesis (fat burning), reduce fat cell formation, and limit fats absorption. (9)

Animal studies suggest that EGCG from green tea can stimulate leptin (a satiety hormone) and reduce food intake.

Together, EGCG and caffeine have a synergistic response in promoting fat burning and metabolic rate. This means that when EGCG and caffeine are added together, they have an even greater effect than either ingredient alone. (10)

May Protect Against Oxidative Stress Caused by Exercise

The major benefit of green tea for athletes and people who exercise may be to protect against oxidative stress (an imbalance between ROS and antioxidants) and muscle damage caused by exercise. (Reduced muscle damage and lower oxidative stress may have a positive impact on exercise performance and recovery.)

But to clarify, research does not consistently support using green tea to increase endurance or exercise performance. (11)

A 2014 study had young men perform resistance exercise and drink 200 mL of a green tea beverage three times per day for a week to see how green tea protected against oxidative stress. (12)

Compared to plain water (200mL 3x/day), the men who drank green tea had reduced oxidative stress caused by exercise and greater levels of antioxidants in their blood.

A 2018 study found that taking green tea extract (500 mg/day) for 15 days reduced muscle damage and oxidative stress, and preserved the brain-muscle connection compared to a placebo. (13)

Related: Pre-Workout Meal: What to Eat Before a Workout

May Reduce Cancer Risk

Green tea may be a good support to cancer prevention and may enhance the activity of anti-cancer drugs.

EGCG primarily helps reduce cancer progression by increasing the activation of antioxidants and inhibiting inflammation.

Inhibition of certain inflammatory cell-signaling molecules can decrease cancer initiation, progression, and spread.

Not all cancer types show the same degree of responsiveness to EGCG, but a 2020 review shows that EGCG can positively impact overall inflammation and prevent the spread of cancer in cell studies. (14)

Clinical trials so far find that EGCG plays a role in cancer prevention in cancers of the prostate, urinary bladder, head and neck, breast, ovaries, and lungs. These benefits are promising but are not consistently seen in clinical studies. (15)

In addition, some anticancer medications have an increased effect when combined with EGCG and other tea polyphenols. While more research needs to be done, there is potential for EGCG to be used in cancer treatment and prevention. (14)

Can Support Longevity

While green tea alone may not cause you to live longer, drinking it at least three times per week or more can be a contributing factor to a longer lifespan.

One multi-year study with over 100,000 adult participants examined the risks that contribute to cardiovascular disease and all-cause mortality. (2)

In the study, adults who drank green tea three times or more weekly were likely to have a longer life expectancy (about 15 months longer) than those who drank tea fewer than three times per week.

Another multi-year study in China found that older adults aged 80 or older who drank tea daily had a 10% reduction in mortality compared to infrequent tea drinkers. (16)

Beneficial Compounds of Green Tea

Green tea has been used in Traditional Chinese Medicine and other Asian traditional medicine systems for thousands of years. (17)

Tea was used for its anti-inflammatory properties against a wide variety of conditions. Today, we know that green tea is packed with beneficial compounds for health that make this beverage a superfood. (18)

Here are some of the major beneficial components of green tea.

Polyphenols

Green tea contains several types of polyphenols, compounds with strong antioxidant activity.

This means that they are able to reduce the activity of reactive oxygen species (ROS), molecules that cause oxidative stress and inflammation and increase the risk of chronic diseases. You may also know ROS by the name of “free radicals.”

Most of the polyphenols in green tea come from the “catechins.” Catechin antioxidants were named after the plant they were first discovered in, the Acacia catechu tree. (19)

The major catechins in green tea include epicatechin, epigallocatechin, epicatechin-3-gallate, and epigallocatechin gallate (EGCG). Green tea has greater amounts of catechins than black or oolong tea.

Amino Acids

Green tea contains several amino acids, but most importantly, L-theanine.

L-theanine is an amino acid primarily found in tea and can affect the brain by increasing brain chemicals like GABA, dopamine, serotonin, and alpha waves (a type of brain wave associated with relaxation). (20)

Vitamins and Minerals

Green tea is filled with nutrients (including vitamins, minerals, and trace elements), such as magnesium, iron, copper, phosphorus, potassium, calcium, selenium, zinc, and chromium.

Approximately 5% of the dry weight of green tea is made up of minerals and trace elements.

Caffeine

Green tea tends to have a lower caffeine concentration per cup than black teas or coffee, but can still provide caffeine-related benefits.

How Much Drink Tea Should I Drink?

Across studies for different conditions, drinking 3 to 5 cups of green tea per day is sufficient to experience the benefits of green tea.

Currently, there is no optimal dosing of EGCG.

A scientific panel noted that the average intake of EGCG from green tea beverages ranged from 90 to 300 mg/day, but there is little information on an optimal dose. (21)

Important Safety Considerations

Although tea is the second most consumed beverage in the world, there are still some risks to drinking green tea.

The risks are generally dose-dependent, so paying attention to your intake of green tea and green tea extract is important.

The most commonly reported side effects from drinking green tea or taking capsules of green tea extract include abdominal pain, abdominal discomfort, diarrhea, indigestion, and elevated liver enzymes (a sign of liver toxicity). (22)

In some studies, less common symptoms of green tea intake included vomiting, constipation, gas, and belching.

While some side effects from tea are attributed to the EGCG concentration of green tea products, some side effects are from the caffeine present in green tea. These side effects include anxiety, insomnia, and nervousness.

The FDA warns against excessive amounts of caffeine and recommends limiting caffeine intake to no more than 400 mg daily (approximately 14 cups of green tea). (23)

Depending on the region, daily intake of tea typically ranges between 3 to 10 cups. To determine the right amount of tea for you, monitor your reactions to tea and when you feel any adverse effects.

Studies support that green tea is better tolerated in beverage form, and green tea extract capsules should be taken with a meal or after eating to reduce symptoms. (22)

Intake of 800 mg of EGCG or more as a supplement is associated with increased liver enzymes. (21)

Medication Interactions

Green tea and EGCG can interact with several types of medications. Some medications are made more bioavailable (more absorbable by the body), while others are decreased in bioavailability and activity. (24, 25)

EGCG and other tea polyphenols can increase the activity of certain anticancer medications, blood pressure medications (calcium channel blockers), aspirin, warfarin, antibiotics, and estrogen modulators (e.g., hormonal treatments for breast cancer).

EGCG and green tea extract can reduce the bioavailability or interaction with certain antipsychotic medications, anticancer medications, mood medications, sedatives, and beta-blockers

Nutrient Interactions

Excessive green tea intake may impact the absorption of certain minerals. Catechins in green tea are able to bind to zinc and iron and reduce blood concentrations of these minerals. (26)

People with a history of iron deficiency should take caution with the timing of iron-containing foods or supplements and drink tea at least an hour after meals.

Conversely, excessive green tea can also increase manganese concentration in the blood.

Green Tea and Pregnancy

Though green tea is low in caffeine, pregnant people should avoid intake of caffeine as much as possible.

A 2021 review of meta-analyses and observational studies found that any caffeine intake during pregnancy increased the risk for miscarriage, stillbirth, low birth weight, and childhood acute leukemia. (27)

Speak with your doctor before starting a green tea extract, EGCG supplement, or if you’re drinking large quantities of tea daily to be sure that you can do so safely.

If you experience any significant symptoms, including symptoms that indicate liver injury (e.g., jaundice, dark urine, or abdominal pain), stop immediately and consult your physician.

Tips on Choosing the Best Green Tea

Green tea is widely available, and it can be overwhelming to choose the right kind for you.

It’s available as extracts, powders, individual tea bags, loose leaves, and even pre-brewed bottles for your convenience.

The best green tea to get would have to be loose leaf tea. It is less processed than other teas, meaning its antioxidant content is likely higher than other forms.

If you’re unable to get loose leaf teas or prefer the convenience of prepackaged tea, then be sure to look for high-quality tea brands.

Qualities in a good green tea brand include using hand-picked tea leaves, transparency about where the tea was grown, organic tea leaves, unbleached tea bags, third-party testing, and the use of whole leaves.

The flavor and antioxidant content tend to be better in certain brands, making the additional cost worth the investment.

Higher quality teas are also less likely to be tampered with, contaminated with dangerous chemicals, or contain unnecessary ingredients.

Third-party testing entities like ConsumerLab test the EGCG content of popular green tea supplements and tea leaves.

Some companies will also provide information about the antioxidant content of their products.

Types of Green Tea

Not all green tea is made the same. Some common varieties of green tea include matcha, sencha, and gunpowder green tea, though there are many other Chinese and Japanese varieties of green tea.

You can also commonly find green teas infused with mint, jasmine, and other flavors.

Matcha tends to have a higher concentration of EGCG, and gunpowder green tea has more caffeine due to its processing, but all green tea varieties have benefits.

When it comes down to it, sometimes the biggest deciding factor in choosing a tea is the flavor. Jasmine and mint-flavored green teas tend to be easier on the palate, while matcha green tea has a distinct green, somewhat bitter flavor.

Frequently Asked Questions

The Bottom Line

Green tea is one of the oldest medicinal herbs in history, and modern research confirms its benefits for the body.

Its antioxidant and nutrient capacity make it a kind of “superfood” with many health benefits, including increased lifespan.

While there is still more to learn about green tea and its individual components, the current research is promising.

As with most things, moderation is key. Green tea is one of the most commonly consumed beverages around the world, but excess green tea or extracts from tea can result in negative effects on the gastrointestinal system or liver.

There are also additional risks for pregnant people, people who take certain medications, and those who are sensitive to caffeine.

Before increasing your tea intake or starting a green tea supplement, speak with your healthcare provider to confirm that it is safe for your personal use.