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33 Science-Backed Health Benefits and 19 Side Effects of Green Tea

I love green tea. I drink it every day. If you knew how beneficial it can be, you would be drinking it too.

There are so many varieties of this tea, it is hardly possible to keep track of all of them. Green tea ensures that you can choose just the type of flavor you want: mild, strong, or something in between.

What sets Green tea apart from the other types of teas from this family (like Black tea), is the fact that it is not fermented. Green tea is prepared from tea leaves and is considered a zero calorie drink, even though a cup of unsweetened tea contains a couple of calories.

I hope this post will be able to convince you that if you haven’t yet done so, you should include this potent beverage into your diet. At the very least, you should drink one cup of Green tea a day, and possibly at least a couple of them.

Also, I will provide a list of side effects, and you should check them to find out if drinking Green tea in excess is the best strategy for you.

For example, the biologically active compounds found in Green tea called catechins have great health benefits, especially in terms of lowering cholesterol or reducing the risks of cardiovascular diseases and cancer.

However, if you drink excessive quantities of Green tea, or if you use pure Green tea leave extract in high dosage (like, for example, the ones you would find in weight loss pills and supplements), these compounds may lead to liver toxicity and other problems.

All in all, it seems that for many conditions the benefits of Green tea are related to moderate tea consumption. If you take too much of it, the opposite of what you want to achieve may happen (see the Side Effects section).

Let’s see first what the most important health benefits of Green Tea are.

Health Facts

From this type of tea scientists have managed to extract more than 450 bioactive compounds. To maximize the health benefits, prepare your own tea and use fresh leaves.

  1. Green tea can help you lose weight by speeding up your metabolism and helping you burn calories much faster than usual. [1] The most active components are the polyphenols, one of which is catechins — a type of antioxidant that does a great job in regulating body fat.
  2. Green tea also helps maintain healthy weight, once you have managed to lose your extra pounds. [2]
  3. Green tea has antifungal, antibacterial, and antioxidant compounds.
  4. Regular consumption of green tea can prevent the occurrence of diabetes type 2. [3] The effect could be a result of the anthocyanidins and flavan-3-ols found in this tea, which are great for improving the insulin resistance and glycemic control.
  5. If you suffer from high blood pressure, include green tea to your diet. Its polyphenols will help your arteries widen and as a result your blood pressure will decrease.
  6. The flavonoids from Green tea promote a healthy heart and lower your risks of high blood pressure by as much as 50 percent.[4]
  7. If you suffer from high LDL cholesterol and triglycerides, Green tea should be your beverage of choice. Studies show it can reduce the risks of cardiovascular problems. [5] Because of this, the active compounds from Green tea prevent arterial disease as well. The lowering of cholesterol is believed to be a result of Green tea’s antioxidant called EGCG.
  8. The anti inflammatory features of Green tea help prevent inflammation of the gums and makes your gums healthier. [6]
  9. The active compounds lutein, zeaxanthin, vitamin E, and vitamin C from Green tea strengthen the eye tissue and help improve eye health. This tea is a great protective measure against glaucoma. [7]
  10. The catechins from Green tea are very powerful antioxidants that help reduce inflammation in the joints. In particular, they reduce a special protein called interleukin 8, which causes inflammation.[8]
  11. This tea can bring relief from seasonal allergies. A biologically active compound in Green tea called methylated epigallocatechin gallate may help block the receptor cells responsible for allergic reactions.[9]
  12. If you have irritable bowel syndrome (accompanied with bloating, diarrhea, and constipation), Green tea can come to your rescue. Caffeine from Green tea is what makes the job done because of improving the gut microbiom, despite its other potentially negative effects. [10]
  13. For gut related issues, drink your Green tea hot.
  14. Green tea may help alleviate symptoms of depression and anxiety. [11]
  15. The antibacterial properties of the Green tea leaves can help you flush your body from germs and various strains of harmful bacteria.[12]
  16. Because of its polyphenol content, this tea may offer some relief to patients suffering from Parkinson’s disease. [13] Regular consumption of Green tea seems to have a potent neuro-protective effects as well.
  17. Alzheimer’s disease is another problem where Green tea may help, both in prevention and active fighting. The reason behind these claims is the protection against the formation of beta-amyloid plaque, which is thought the leading factor for dementia. [14]
  18. The flavonoid named epicatechin can help protect brain cells and promote the formation of brain vessels in the brain. Besides in Green tea, Epicatechin is found in cocoa, blueberries, and grapes.
  19. Green tea also stimulates memory and cognitive function. [15]
  20. Migraines are severe headaches characterized by throbbing pain, vomiting, and light sensitivity. Green tea is believed to be of help, both because of its caffeine content, and due to its anti-inflammatory compounds.
  21. This tea is a well known cancer fighting remedy. The EGCG found in Green tea is proven to inhibit the growth of cancer cells. [16] The biological mechanism of action is threefold. First, by lowering the body levels of cyclin D1, which is a protein necessary for malignant cell growth. Second, by a direct elimination of malignant cells, and third, by preventing blood vessels from being formed within the tumor.
  22. Green tea is especially good to help prevent cervical cancer and HPV. [17]
  23. Bad breath is caused by bacteria in your mouth. The natural anti-bacterial properties of Green tea will help you deal with this problem. [18] You don’t have to resort to other measures, like chewing gums loaded with artificial sweeteners. You can use the natural freshening properties of this tea.
  24. Green tea is a know remedy for common cold. The reason is simple, it has all the necessary weapons — a lot of antioxidants, antibacterial and anti-inflammatory compounds.
  25. The active compounds of Green tea are capable of penetrating kidney stones. changing their shape, and flushing them from your body. [19]
  26. Chronic fatigue is a condition characterized by severe fatigue, fever, and depression. The theanine from Green tea, a powerful antioxidant, is held responsible for the beneficial action in this case. Theanine helps boost energy, T cell count, and it also provides more dopamine. [20]
  27. Athlete’s Foot can be treated with Green tea baths and soaks. Daily application may help subside the infection around the toes and soles. [21]
  28. If you are a smoker, you can red drink Green tea to help you diminish the harmful effects of smoking, and at the same time inhibit the urge to smoke. [22]
  29. The nutritional content of Green tea, such as folate, potassium, manganese, and caffeine is beneficial for the skin. Just by drinking Green tea you make your skin look younger and more beautiful. The antioxidant and anti-inflammatory properties of this tea can help you treat acne and other skin conditions. [23]
  30. Green tea is also good for your bone health. As a result of its catechins, it promotes bone growth and bone materialization. [24]
  31. Green tea is a great hangover cure. The poly-phenol content in Green tea prevent liver damage after drinking too much alcoholic drinks and keep it safe after.
  32. This tea will improve your endurance and help you avoid muscle cramps if you drink a cup of hot tea before your next big workout.
  33. Boil yourself a brew of Green tea for UV protection. The antioxidants in this tea will make your skin resistant to UV light, which will also prevent wrinkles from developing.

Possible Side Effects

When talking about the side effects of Green tea, you should have two things in mind: quality and quantity. Quality usually means organic Green tea of high quality, which also usually mean more expensive brands. Quantity means that you should drink it in moderation, which is up to 3 or 4 cups a day for most people.

  1. Green tea contains less caffeine than coffee, but there’s still quite a bit of it. Too much Green tea can contribute to stress, insomnia, anxiety, constipation, and peptic ulcers. How much caffeine does your body tolerate? You have to ask yourself this question and the answer is usually different for every one of us. Find out what your level is.
  2. Green tea may temper with iron absorption by your body. The reason is that the poly-phenols from Green tea bind to iron from foods and prevent its absorption. In the long run, this may even lead to anemia. [25]
  3. Don’t drink Green tea along with iron rich foods. If you do, the main anti-inflammatory compound EGCG, as well as the tannins, loses its beneficial anti-inflammatory action.
  4. Again because of caffeine, Green tea may cause headaches and dizziness. The maximum dose tolerated by humans is approximately 25 cups a day. [26] This is, of course, the extreme that nobody should even try to come close to. Note that some people may be extremely sensitive to Green tea and other caffeine rich teas, where even one or two cups may cause problems.
  5. Green tea may cause problems with insomnia, especially if you take it late in the day. It is known that caffeine takes time to be eliminated from the bloodstream, so make sure you give your body some time without drinking any caffeine beverage before going to bed.
  6. Lactating women should also limit their Green tea consumption, because caffeine is able to pass to the milk and then cause sleep troubles in infants.
  7. Caffeine from Green tea can lead to irregular heartbeat (palpitations) as well. This can be a very serious condition, so be careful in case you suffer from heart disease or you have had problems with irregular heartbeat in the past.
  8. Believe it or not, Green tea can trigger vomiting if taken in larger quantities, again due to the caffeine content. Moderate amounts, up to 500 mg a day, shouldn’t be a problem, but even then, some people are more sensitive than others.
  9. Another problem and possible side effect of Green tea is heartburn. The reason is simple: Green tea is acidic, so it may increase the acidity in the stomach, which in turn may irritate the lining in the stomach, leading to heartburn and acid reflux. Normal Green tea that you would prepare on your own doesn’t pose a big problem. The purchased one, however, when fortified with ascorbic acid (Vitamin C), can be a problem.
  10. Again due to caffeine, Green tea may worsen the health condition known as tinnitus. Tinnitus, or ringing in the ears, is reportedly aggravated by drinking caffeinated drinks. A good tea for this condition is ginkgo tea.
  11. Diarrhea is one of the Green tea side effects. It often comes in combination with stomach gas. You may encounter this problem if you are knew to this drink or if you take larger quantities of it. If you drink Green tea together with consuming other foods, this effect may not be so pronounced.
  12. Green tea may cause folic acid deficiency. It interferes with the normal process of absorption of folic acid in the body. This is especially important for pregnant women, as the folates are crucial for the normal development of the fetus.
  13. Beware of Green tea (and other caffeinated drinks) if you have glaucoma. It may increase the pressure in your eyes and worsen your condition. The effect may last up to 2 hours from the moment of drinking this tea.
  14. While the polyphenols in Green tea may be beneficial if you have high blood pressure, at the same time the caffeine may contribute to high blood pressure. So be careful, especially if you use hypertension medications, like nadolol, for example.
  15. Caffeine is known to stimulate the adrenal glands, which in turn may also raise blood pressure.
  16. Caffeine also prevents calcium absorption. So go easy on Green tea if you have increased risks of osteoporosis. The same mechanism may lead to teeth weakening.
  17. Excessive Green tea intake may also cause kidney damage. This is especially true for Green tea extract.
  18. The catechins from Green tea, especially if you drink it in large quantities, may disrupt the function of the thyroid gland. If you take thyroid medications, consult with your doctor about how much Green tea is acceptable.
  19. Keep in mind that all drinks that contain caffeine are natural diuretics, which can be beneficial, but too much of these beverages may even aggravate the bladder if you are sensitive.

The Bottom Line

As it is often the case with power drinks, supplements, and super foods, don’t be blindsided by the hype that often follows them. Do your own research. Green tea is no exception!

Green tea can be extremely useful, but also potentially dangerous in some situations.

Especially if you use it as in a form of extract. Or if you are pregnant.

Examine your current health profile and nutritional needs, and decide accordingly. Consult an experienced expert if you have to, and make an informed decision.

To your health!


[1] Can green tea preparations help with weight loss?

[2] The effects of green tea on weight loss and weight maintenance: a meta-analysis.

[3] The Effects of Green Tea on Obesity and Type 2 Diabetes

[4] Tea Drinkers Reap Blood Pressure Benefits

[5] Green tea and heart health

[6] Green tea: A boon for periodontal and general health

[7] Green Tea: The Eyes Have It


[9] Anti-Allergic Action ofO-methylated EGCG in Green TeaCultivar Benifuuki

[10] Intestinal microbiota, probiotics and mental health: from Metchnikoff to modern advances: Part II – contemporary contextual research

[11] Green Tea Benefits: New Research And Well-Known Reasons To Sip Now

[12] Effects of green tea on Escherichia coli as a uropathogen.

[13] Green Tea May Protect Against Effects Of Parkinson’s Disease

[14] Green tea extract enhances parieto-frontal connectivity during working memory processing.

[15] Green tea extract enhances parieto-frontal connectivity during working memory processing

[16] Cancer and metastasis: prevention and treatment by green tea

[17] Green Tea Extract in Preventing Cervical Cancer in Patients With Human Papillomavirus and Low-Grade Cervical Intraepithelial Neoplasia

[18] Effect of green tea on volatile sulfur compounds in mouth air.

[19] Effects of green tea on urinary stone formation: an in vivo and in vitro study.

[20] Green tea extract and catechin ameliorate chronic fatigue-induced oxidative stress in mice.

[21] Athlete’s foot: Overview

[22] Green tea and prevention of esophageal and lung cancers

[23] Green tea in dermatology.

[24] Green Tea and Bone metabolism

[25] Iron deficiency anemia due to excessive green tea drinking.


4 Comments on 33 Science-Backed Health Benefits and 19 Side Effects of Green Tea

  1. “Indians love tea very much and it’s the most drink beverage in entire India, hence I suggest this should be in the purest form and hence organic india tulsi green tea is best for both children , adults and old women.
    Greetings from India
    Keep bringing more!!”

  2. great post! thanks for sharing

  3. I always have green tea when I have dinner.

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