Are There Any Side Effects of Green Tea?

Health and Nutrition

Green tea is prepared from Camellia sinensis leaves and buds that have not undergone the same withering and oxidation process used to make Oolong teas and black teas. Green tea is being used for its medicinal value since ancient times. 

Green tea has been endowed with a large number of health benefits. Green tea has antioxidant activity, anticarcinogenic activity and so on. But nothing is good when taken in excessive amounts. Here are a few reasons why you should take green tea in moderation.

Side effects of green tea if taken in excessive amounts

Caffeine in green tea and its side effects

Caffeine is the most commonly consumed psychoactive drug in the world (1).

Green tea contains caffeine along with other constituents such as catechins. A cup of green tea (180 to 240 ml) may contain about 30 to 60 mg of caffeine (2).

Based on the literature reviewed it was concluded that a healthy adult can take up to 400 mg of caffeine that is equivalent to 6 mg per kg body weight. This amount was not linked to any negative effects such as cardiovascular system, bones, calcium balance, behaviour or any other system in the body (3). 

The consumption of less than 200 mg of caffeine is recommended for pregnant and lactating women (4, 5). One gets caffeine from other sources such as chocolates, coffee, desserts, some medications etc throughout the day. 

Therefore, to avoid any adverse effects pregnant and lactating women should keep green tea consumption to the minimum one or two cups a day based on the other foods with caffeine they consume.

Green tea tannins affect iron absorption

Tannins in green tea have the effect of binding with non-heme iron, that is the iron from plant sources (2). Therefore, it affects the iron absorption in the body. Do not have tea for a couple of hours after a meal to make sure maximum iron is absorbed. 

According to a case report excessive green tea consumption may lead to iron deficiency anaemia (6).

Green tea and dehydration

Green tea is a natural diuretic. Intake of more than 5 cups of green tea may cause excessive urination. This condition may lead to dehydration and electrolyte imbalance (2). Dehydration may again cause other symptoms such as headaches, fatigue and altered heart rate (2).


Green tea and folate

Green tea constituents also may inhibit absorption of folate, that is another form of B vitamin folic acid, which may also lead to anaemia (2).

Final word

Everything is good in moderation. 2 cups of green tea a day would be a decent amount to take. There are several foods in nature which contribute towards health so why not take a variety of foods and beverages in moderation.

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  1. Temple, J. L., Bernard, C., Lipshultz, S. E., Czachor, J. D., Westphal, J. A. and Mestre, M. A. (2017) The Safety of Ingested Caffeine: A Comprehensive Review, Frontiers in psychiatry. Vol. 8 (80).


  1. Nawab, A. and Farooq, N. (2015) Review on green tea constituents and its negative effects, The Pharma Innovation Journal. Vol. 4 (1).


  1. Nawrot, P., Jordan, S., Eastwood, J., Rotstein, J., Hugenholtz, A. and Feeley, M. (2003) Effects of caffeine on human health, Food Additives & Contaminants. Vol. 20 (1).


  1. American College of Obstetricians and Gynaecologists, Women’s health care physicians (2010). Moderate Caffeine Consumption during Pregnancy.


  1. EFSA NDA Panel (Europeon Food Safety Authority Panel on Dietetic Products, Nutrition and Allergies). (2015) Scientific Opinion on the safety of caffeine, EFSA Journal. Vol. 13 (5).


  1. Fan, F. S. (2016) Iron deficiency anemia due to excessive green tea drinking, Clinical case reports. Vol. 4(11).


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