Green Tea Health Benefits and Side Effects

Written by: Christopher Karam | ✔️ Medically Reviewed by: Dr. Riad M., M.D - G.P and Micheal B., M.D | Last Updated: 2020 June 24

What Is Green Tea?

Green tea is one of the many variations of non-herbal teas that contain caffeine. Originating from the Camellia Sinensis plant in China, it’s also used to make black tea, oolong tea, white tea, and matcha.

Green tea is made from Camellia Sinensis leaves that haven’t undergone any strenuous processing or chemical treatments. Tea leaves are dried by either drying or steaming, preventing oxidation and preserving flavor.

Similarly to that of oolong tea and black tea, there are many health benefits to drinking green tea as it retains the most amount of antioxidants and polyphenols. Due to its natural methods of production, it retains a good amount of caffeine and chlorophyll.

matcha tea outdoors

The Origin and History of Green Tea

Older civilizations first started to consume green tea is believed to be first brewed back around 2700 BC during the reign of the Emperor Shennong, in China. He was the primary contributor to ancient Chinese medicine, discovered when the fresh tea leaves of a nearby tree fell into a cup of boiling water.

Although green tea originated in China, its production and manufacturing methods have spread out to many other countries in Asia, Europe, and North America.

Green tea is a calorie-free drink containings around 34 mg of caffeine per serving. Caffeine helps to manage and suppress hunger, food cravings, and regulate blood sugar levels.

The best part about green tea’s caffeine content is that, unlike coffee, it gets released at a slow and steady pace for a few hours after drinking it, avoiding a spike and crash of energy.

Green tea is one of the healthiest beverages you can have in large doses and have minimal side effects. Unless you suffer from a few heart-related diseases, severe anxiety, or people who are taking blood thinners.

Also, green tea is considered to be an anti-ageing drink because of its large amount of antioxidants, nutrients, and vitamins that are excellent for your health.

There are many health benefits and side effects of green tea caffeine and chlorophyll levels.

All having been beneficial effects for the use in traditional Indian medicine to clot blood, controls internal and external bleeding, heal wounds, improve digestion, improve iron absorption, regulate body temperature, as well as improve cardiovascular and mental health.

Traditional green tea drinkers prefer a herb blend that hasn't been mixed with any kind of sugar, only consumed in its pure and natural state. It has been used in medical practices for thousands of years, even to this day.

Many studies proved that it's effective for preventing the flu, high blood pressure, prostate cancer, breast cancer, promoting weight loss, dilate blood vessels, bleeding disorders, and reducing the risk of certain types of cancer.

The mild amount of caffeine in green tea improves various brain functions and helps you concentrate better.

If you are feeling a mid-afternoon slump, brew yourself some herbal teas instead of a cup of coffee to elevate your mood, increases your energy levels, and enhance your productivity.

matcha tea

There are tons of ready to go green tea products available that are bottled and usually sweetened with sugar or artificial sweeteners.

These variations include single tea bags, loose-leaf, steeped, and instant tea powder forms. You have even more options for green tea products that are available online.

It’s a good idea to compare different brands and different types of herbal teas when looking to choose the most suitable one for you.

Ideally, a brand that’s using little to no sugar, sources the plants safely with no chemical treatments and has no heavy metals such as lead, arsenic, and cadmium.

It’s considered that green tea is one of the healthiest drinks on the planet because certain types of green tea have the highest levels of antioxidants out of any other tea.

Additionally, a research article shows that the natural chemicals called polyphenols found in the tea leaves is the main contributor to its anti-inflammatory and anti-carcinogenic reactions.

Drinking green tea has also been shown to stimulate happiness and cheer up patients suffering from depression, boosting mental health and alertness due to its caffeine content and polyphenols.

While being free of any essential oils, it has approximately 20% to 45% of its mass being polyphenols, of which 60% to 80% are catechins such as EGCG. EGCG is also known as Epigallocatechin Gallate, a type of catechin that's most abundantly found in tea.

Catechins are important plant-based metabolites, which are antioxidants that are said to help prevent free radical damage, oxidation, cell degeneration, increase endurance capacity and energy levels.

The main side effect of green tea supplements is that they contain high levels of live active substances that can trigger harmful reactions and have bad interactions with other herbs, supplements, and medications.

dry sencha green tea

Before producing the green tea, the leaves need to go through certain procedures which leads to a successful product. Afterwards, the green tea leaves are prepared in many different ways, based on the type of tea the company wants.

There are several variations of green tea that exist, which differ considerably on the variation of Camellia Sinensis plant used, growth and weather conditions, agricultural method, treatment during manufacturing, and the time of harvesting.

It’s prepared using either traditional or higher-quality modern techniques. These tea leaves are either they're sun-dried, cooked over charcoal, or heated on a skillet are all traditional processing methods.

They’re usually harvested 3 times per year, the first set of leaves are collected between late April and May, while the next harvest typically happens between June and July, and the third’s from late July to August.

After all of the gathering, the processing goes through various stages depending on the blend and type of tea you want. There are 2 basic ways to make green tea, either the traditional method or the modern method, both of which can be modified by the producer.

Multiple different types of tea originate from China or Japan, here’s the complete variation list of green teas:

  • Gunpowder Tea

  • Longjing or Dragonwell Tea

  • Pi Lo Chun or Spring green snail Tea

  • Snowy Mountain Jian Tea

  • Hyson or Lucky Dragon Tea

  • Kaihua Longding Tea

  • Xinyang Mao Jian Tea

  • Tian Mu Qing Ding Tea

  • Taiping Hou Kui Tea

  • Gyokuro Tea

  • Sencha Tea

  • Bancha Tea

  • Matcha Tea

  • Hojicha Tea

  • Genmaicha Tea

  • Kukicha Tea

These different types of green tea variations all offer the same positive impact but the only difference is their harvesting methods, dates, and production methods.

camellia sinensis plant

Green Tea Health Benefits

The U.S National Cancer Institute (NCI) claims that regularly having green tea can have some amazing health benefits due to all of its nutrition, amino acids, antioxidants, and catechins compounds.

Here are some of the green tea nutrition facts with the recommended daily values (DV), serving size: 1 cup (245 grams):

  • Total calories: 2.5 kcals

  • Total fat: 0 g

  • Saturated fat: 0 g

  • Dietary fiber: 0 g

  • Trans fat: 0 g

  • Sodium: 2.5 mg

  • Potassium: 20 mg (1% of the DV)

  • Protein: 0.5g

The green tea nutrition facts have a fantastic ratio of macronutrients that are great for promoting the removal of abdominal fat, which is also amplified by its caffeine content.

Below is the complete list of health benefits of green tea, you'll see great results when its included into your daily diet.

1. Causes Weight Loss and Suppresses Hunger

Drinking green tea increases your metabolism and has effective fat-burning properties. That's because it contains epicatechin which helps you lose weight and reduces the risk of becoming overweight or a reduced risk of obesity.

Furthermore, multiple studies have shown that people who drink green tea regularly can maintain a healthy weight mass after a significant weight loss treatment.

Drinking green tea regularly also helps to suppress your appetite and keeps your energy levels consistent, resulting in fewer hunger cravings and fewer calories consumed throughout the day due to its high caffeine content.

2. Green Tea Caffeine Boosts Your Brain Health and Function

A major part of green tea’s health benefits is its positive effect on mental health. Green tea boosts cognitive functions, specifically your active working memory.

It will protect your brain from calcification and preserve your mental health in the long term, reducing your risk of Alzheimer’s Disease.

A study carried out on mice showed that green tea can protect brain cells from premature deaths, prevents oxidative damage, and restores damaged brain neurons.

This also proves that green tea has the potential to reduce the risk of neurodegenerative diseases like Alzheimer’s and Parkinson’s.

cup of green tea

3. Helps Fight and Reduces the Risk of Cancer

There are many powerful antioxidants found in green tea. They’re called epigallocatechin gallates and polyphenols, several research articles suggest they help your body slow down and kill cancerous cells without affecting or damaging any surrounding healthy tissues and also improving brain function.

Multiple clinical studies show how the polyphenols in green tea can benefit you by inhibiting tumor cell proliferation directly contributing to cancer prevention in human and animal studies.

It also protects damage coming from ultraviolet (UV) and UVB radiation, easily scavenges and destroys free radicals, and activates detoxification enzymes such as glutathione S-transferase and quinone reductase that defends against tumor development.

The cancers that can be offset or have a reduced effect on are:

  • Pancreatic

  • Lung

  • Skin

  • Breast cancer

  • Prostate cancer

  • Colorectal cancer

  • Stomach cancer

4. Stabilizes Blood Sugar Levels and Prevents Type 2 Diabetes

Green tea caffeine helps to reduce the risk of developing type 2 diabetes. This is because it lowers your blood sugar levels, stabilizes your glucose levels when eating any foods containing sugar, and lowers bad LDL cholesterol.

Diabetics lose their insulin sensitivity, which means insulin is less effective at signalling cells to absorb sugar from the bloodstream, resulting in both higher blood insulin and sugar levels.

Therefore, the more sensitive you are to insulin, the lower your normal blood sugar levels would be. That's much more beneficial since both sugar and insulin are damaging to your cardiovascular system and are the leading cause of the development of type 2 diabetes.

dry green tea herbs

5. Reduces Risk of Heart Disease

The antioxidant content in green tea protects the heart and prevents diseases. Drinking green tea regularly has also shown to dramatically increase the antioxidant capacity in your blood. Resulting in the protection of the heart from reactive oxygen species and prevents heart attacks.

A cross-over study published from the journal of the American Heart Association (AHA), noted that consuming 4 to 5 cups of green tea per day was associated with a small reduction in systolic blood pressure, similar to oolong tea.

The American Medical Association (AMA) had a study conducted with the Ohsaki National Health Insurance Cohort to see the connection between green tea consumption and the reductions of certain mortalities.

Patients were Japanese adults aged 40 to 79 years old with no history of any heart-related diseases or complications. Separated into 2 groups, followed up with them for either 7 or 11 years. They compared death rates with causes such as cardiovascular disease, cancer risk, and other hazards.

They found that green tea consumption was associated with a reduced risk of death from heart disease itself and its causes, but found no difference with cancer prevention.

6. Improves Oral Health and Prevents Tooth Decay

Some of the most controversial nutrition facts in green tea is that it contains fluoride and caffeine, fluoride is a mineral that is sometimes added to the water supply to support stronger dental health, otherwise, it's naturally found in the water of fluoridated regions.

pouring hot tea

The fluoride content found in water and black tea leaves is so minuscule that half of it gets absorbed by our bones and the rest gets secreted. It would take around 18,000x times the fluoride content in all of those cups of green tea to cause serious harm or potential death.

If anything the caffeine will cause more harm, you'd need 500 cups of green or black tea taken in the span of a few hours to cause serious harm and even cause death. When you look at coffee, you'd need about 100 cups of coffee to cause harm or death.

Green tea also reduces inflammation and limits the growth of certain bacteria and inhibits viruses like the influenza virus. The influenza virus can lead to periodontal diseases such as tooth decay, and can also harm your nose, throat, and lungs.

Multiple studies have also stated that people who drank green tea had better oral health than those who didn't.

7. Boosts Muscular and Physical Performance

The many health benefits of green tea's caffeine content help energize you and prevent fatigue. This naturally boosts your overall muscular and physical performance.

The amino acid L-theanine, as well as the other antioxidants in green tea, helps prevent tissue damage during physical training. A study at Abbott Laboratories found that green tea extract increased muscle mass preservation and function.

8. Improved Skin Health

Green tea has a large mass of EGCG, ECG, and EGCs defend your skin from harmful DNA and cell damage, especially against UV and UVB rays. Supplements can be taken orally or applied directly onto the skin.

clear cup of tea

Taking recurring doses of green tea extract once per day can offer amazing anti-ageing, anti-inflammatory, and anti-bacterial agents for your skin such as:

  • Reducing wrinkles

  • Tightening your skin

  • Reduced risk of skin cancer

  • Treats acne

  • Unclogs pores

  • Exfoliates

  • Reduces redness and irritation

Green Tea Side Effects and Detriments

Some of the side effects of green tea stem from its caffeine, fluoride, and antioxidant levels. These harmful effects can affect anyone, ranging from children to adults.

There are small clinical studies have found out that green tea offers protection against the development of oesophageal cancer, particularly among women. However, one large scaled population-based clinical study found the opposite.

Drinking green tea can be associated with an increased risk of oesophageal cancer. Secondly, the hotter the tea, the greater the risk of damage it can cause to the upper digestive system. If the water you drink is very hot, even in small sips, very hot green tea can still damage the esophagus and lead to long-term permanent damage.

1. Dangers During Pregnancy and Breastfeeding

Most of the side effects of green tea caffeine, tannins, and catechin levels are all linked to an increased risk of miscarriages and birth defects in newborns.

More than 3 cups a day is very dangerous for pregnant women and breastfeeding women, especially because caffeine's transferred through breast milk to the child.

bamboo whisk matcha tea

Even in small doses, green tea has some serious side effects and can be unsafe for pregnant women as well as their children.

So you should consult your doctor and/or physician on your intake of green tea in order not to affect you or your baby. Generally, avoid exceeding 120mg of caffeine per day, a cup of green tea has around 30 to 40mg.

2. Causes Headaches, Vomiting, Anxiety, and Digestive Issues

Another side effect of green tea stemming from excess caffeine intake, it’s possible that green tea can cause headaches, vomiting, nervousness, sleep issues and insomnia, irregular heart rate and palpitations, dizziness, and convulsions. Avoid green tea if you're caffeine-sensitive or have chronic migraines.

A green tea side effect of having too much caffeine can also cause bowel and stomach irritations when taken on an empty stomach, the tannins increase your stomach acid levels which can cause many more issues, such as chronic heartburn, acid reflux, and diarrhea which is partly due to the caffeine as well.

Green tea is also a natural laxative, stimulating your colon frequently. People suffering from irritable bowel syndrome should avoid it altogether.

In high doses, tannins can cause vomiting because of the way the proteins bind to your intestines. Some of these effects can be mitigated when cooler water, brewing with too hot of a kettle can alter the chemical makeup of the leaves and make certain effects even worse.

Practical heat should be between 140°F to 176°F (60°C to 80°F).

3. Causes and Aggravates Bleeding Disorders

The nutrients and vitamins found in green tea will decrease your fibrinogen levels, a blood protein that helps your blood clot, also inhibiting the oxidation of fatty acids which leads to thinner blood. Coupled with high blood pressure, it can cause heart issues such as a stroke or hypertension.

tea leaf farm

Above all, the caffeine in green tea increases bleeding for those that already have a bleeding disorder because of the increased blood pressure, artery pulse speed, and blood vessel dilating reactions. If you're taking blood thinners or anticoagulant drugs, such as Coumadin, Warfarin, or Heparin you should take caution with your tea intake.

4. Can Reduce Sleep Quality and Cause Irritability

Caffeine is an active stimulant which inhibits sleep and heightens your energy levels. This can be problematic for most people who have difficulties falling asleep.

This raises anxiety and cognitive awareness which reduces the secretion of melatonin, which is the sleep signaling hormone keeping your circadian rhythm in order.

Paired with L-theanine, an amino acid that boosts focus and alertness makes these side effects even stronger. L-theanine also works against melatonin production at night time.

5. May Create an Iron Deficiency and Cause Anemia

Green tea has many compounds that reduce iron absorption by your body. A few case studies show that green tea can be harmful and potentially dangerous in people suffering from anemia or having an iron deficiency.

You can prevent this side effect by adding a bit of lemon to your teas, the vitamin C from lemons promotes iron absorption which minimizes the harmful effect of the tannins and catechins stress on the liver.

Alternatively, you can wait 1 to 2 hours after eating to consume green tea, which gives your body enough time to fully digest your food and absorb most of the iron. This makes sure that your liver has enough glucose to process the catechins and tannins.

working with tea leaves

Rating and Recommendation

Extremely Recommended

The health benefits of green tea make it so that it's a perfect addition to almost every diet, from low carb to ketogenic diets.

Green tea should not be taken by pregnant women, people who are anemic, or who have low iron because of some of the vitamins and compounds it contains may affect the baby and even the mother in higher doses.

Also, if you suffer from any heart problems or hypertension, kidney or liver problems, stomach ulcers, or anxiety disorders should not take green tea supplements or extracts. Large amounts of caffeine amplify those existing disorders.

Here’s the full list of nutrition facts and health benefits of green tea:

  1. Causes Weight Loss and Suppresses Hunger

  2. Its Caffeine Boosts Your Brain Health and Function

  3. Helps Fight and Reduces the Risk of Cancer

  4. Stabilizes Blood Sugar Levels and Prevents Type 2 Diabetes

  5. Reduces Rate of Heart Disease and Improves Heart Health

  6. Improves Oral Health and Prevents Tooth Decay

  7. Boosts Muscular and Physical Performance

  8. Improved Skin Health

The list of side effects of green tea:

  1. Possible Dangers During Pregnancy and With Breastfeeding

  2. Causes Headaches, Vomiting, Anxiety, and Digestive Issues

  3. Causes and Aggravates Bleeding Disorders

  4. Can Reduce Sleep Quality and Cause Irritability

  5. May Create an Iron Deficiency and Cause Anemia

running track

If you suffer from any of these complications, green tea is objectively a bad choice unless told otherwise by a healthcare practitioner.

Those taking anticoagulant drugs such as Warfarin, Coumadin, or Jantoven should drink green tea with caution due to its vitamin K content, which is necessary for blood coagulation.

Avoid drinking too much green tea on an empty stomach since it causes liver damage in more concentrated and higher doses, stick to 1 cup. Alternatively, having some during a meal can hinder iron absorption.

Ideally, should have a single cup of green tea 2 hours before or after a meal, and not exceeding 2 to 3 cups a day. Always consult your doctor or health care professional for advice that's specifically applicable to you.

If you have none of the characteristics above, green tea can be a powerhouse of nutrition, caffeine, and energy that can shape up and boost your whole diet.

Frequently Asked Questions

Drinking green tea offers a wide range of health benefits.

It's often considered one of the healthiest drinks on the planet, balancing antioxidants with caffeine as well as plant-based compounds like catechins and polyphenols, which extends its list of health benefits even further.

It's full of antioxidants that help your body fight off infections and certain cancers, and the caffeine levels help boost your brain health and functioning.

The list of all of the health benefits of green tea are:

1. Causes Weight Loss and Suppresses Hunger

2. Its Caffeine Boosts Your Brain Health and Function

3. Helps Fight and Reduces the Risk of Cancer

4. Stabilizes Blood Sugar Levels and Prevents Type 2 Diabetes

5. Reduces Rate of Heart Disease and Improves Heart Health

6. Improves Oral Health and Prevents Tooth Decay

7. Boosts Muscular and Physical Performance

8. Improved Skin Health

Green tea also has a few side effects that concern a minority of the population, aggravating certain existing disorders and symptoms. It shouldn't be taken by anyone who is/are:

1. Pregnant

2. Have existing digestive issues

3. Bleeding disorders

4. Insomnia

5. An iron deficiency

Green tea is the easiest type of non-herbal tea to prepare. All you need is water and a way to heat it, high-quality green tea leaves (US), a cup or kettle.

1. Take a cup or a kettle and fill it with hot water.

2. For each cup of water, add 1 tablespoon of tea leaves to your cup or in the kettle of hot water.

3. Let the leaves steep for 3 to 5 minutes. Adding any sugar or honey if needed.

4. Enjoy!

Making matcha takes more work, but tastes a lot better and has the same health benefits as regular green tea.

You'll need a bamboo whisk or a regular one, a bowl, matcha powder (US) , a sift is optional. This is how you make matcha green tea:

1. Add non boiling hot water into the bowl.

2. Sift 1 to 2 teaspoons of matcha powder into a bowl for each cup of water that was added. Around 8 to 12 teaspoons go into a kettle, depending on how strong you like it.

3. Using a bamboo whisk or regular whisk, stir the water in a zig-zag "W" like motion for up to 2 minutes until the top forms a nice layer of foam.

4. Enjoy!

Green tea is great for helping you lose weight and increase your metabolism. Multiple studies show how including green tea into your daily diet can help you lose body fat.

A study conducted on the daily consumption of green tea over 3 months had an average of around 1 pound of fat burned per month.

Specifically, green tea helps you lose abdominal fat through its plant-based compounds and antioxidants. Body fat is used to store toxins.

Since abdominal is the fat layer that stores the most toxins having the largest surface area, green teas antioxidants will visually eliminate fat from the abdominal area.

The compounds that help you lose weight, is its caffeine, chlorophyll, and flavonoid content. These could all individually increase your basal metabolic rate.

A study revealed that over a 24 hour window and having consumed the equivalent of 3 cups. If you maintain a consistent dosage every day for 1 week, in the following days, you can look to lose around 100 calories per day if taken consistently.

Green tea is widely available in many commercial online retailers such as Amazon (US) (CA) and Walmart, your local retailers, as well as in almost every coffee shop or cafe in your area.

The explosion of popularity made it so you can buy matcha powder almost anywhere. Supermarkets to online retailers all have a form of matcha powder for sale. Such as David's Tea, Amazon (US) (CA), and Walmart.

Articles and Sources

cup of green tea

Green Tea Nutrition Facts

Serving Size 245 g (about 8oz or 1 Cup)

Amount Per Serving
Calories 2.5 Calories from Fat 0
% Daily Value*
Total Fat 0 g 0 %
Saturated Fat 0 g 0 %
Polyunsaturated fat 0 g
Monounsaturated fat 0 g
Trans Fat 0 g
Cholesterol 0 mg 0 %
Sodium 2.5 mg 0 %
Potassium 20 mg 1 %
Total Carbohydrate 0 g 0 %
Dietary Fiber 0 g 0 %
Sugars 0 g
Protein 0.5 g
Vitamin A 0 % Vitamin C 0 %
Vitamin E 0 % Vitamin K 0 %
Vitamin D 0 % Vitamin B6 0 %
Calcium 0 % Iron 0 %
Magnesium 0 % Cobalamin 0 %

Calories per gram:

Fat: 9 | Carbohydrate: 4 | Protein: 4

Source: USDA's Nutrient Database

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