What is green tea?
Green tea is a type of tea made from Camellia sinensis, originated in China and is produced in many other countries now. This is the same plant that is used to prepare. It is the same as black tea but there is no fermentation process of the leaves in the case of green tea.
Green tea is composed of several compounds which are natural in plants, moreover it contains compounds that are known as bioactives, which means they can have or can have a biological activity in the human body. The compounds with these associated functions are mainly catechins, epicatechins and theanine., which are part of a group of chemical compounds called polyphenols.
Types of green tea
There are different classifications of green tea, based on leaf shape, flavor,region or time of harvest.
Nutrients we can get from green tea
Notably, the best source of catechins is unfermented green tea. Depending on the type and origin of green tea leaves, their antioxidant properties may be uneven. The main nutrients present are polyphenols, particularly catechin and epigallocatechin galate (EGCG). In lesser amount but also present in green tea, there can be, moreover the processing of green tea also changes nutrient content.
Green tea health benefits
A lot of scientific research has been conducted in laboratories to understand the benefits green tea , using cells derived from humans or animals, and the suggested benefits are the following:
- Caffeine content for brain function and L-theanine
- Reduce cognitive decline
- Cardiovascular disease
- Weight loss, burning fat and boosting metabolic rate
- Glycemic/blood sugar content- lowered the risk of type 2 diabetes
- Could lower Cholesterol and subsequently inflammation
- Antioxidants help prevent cell damage and formation of free radicals in the body
Moreover, some of these effects have also been reported in the scientific literature in studies from different geographical regions and thus, support some of the previous claims of beneficial effects of green tea on health. These studies can be further read and found in the references, and although benefits have been found in these many studies,
but they are not completely conclusive as the impact of green tea on metabolism is still an area of study for scientists.
Side effect and risks
The main concern and study of the negative effects of green tea is in association with the liver, where a lot of processes such as detoxification of substances in the body occurs. Live injury itself is rare, nonetheless there is evidence in the scientific literature about cases in which oure green tea extracts and other extract containing products caused liver damage after consumption with characteristic symptoms of liver injury, such as jaundice, which is when the skin or whites of the eyes turn yellow.
The understanding of how green tea can act into damaging the liver is part of ongoing research, where the mechanisms involved are yet to be fully understood. The consumption of herbal or dietary supplements should be done with the supervision and advice of healthcare professionals.
Published data shows adverse event case reports associate toxicity to the liver with intake of EGCG amounts from 140 mg to approximately 1000 mg/ day, with susceptibility associated with other factors specific to each individual.
Moreover, the consumption of green tea during pregnancy, breast-feeding should be taken carefully, and upon consultation with a healthcare professional, since it can have effects on the mother or baby's development.
The American Journal of Nursing also states in the best practice recommendations, that in assessing patients for anemia, nurses should ask about their tea intake, since it can interfere with iron absorption and potentially cause anemia.
How much is enough?
According to the National Center for Complementary and Integrative Health (NCCIH) a division of NIH, it is safe to consume up to 8 cups of green tea per day, however , high doses may interact with certain medications. The potential interactions with medicines is something you discuss with your healthcare practitioner to prevent any side effects.
Moreover, the dosage of the bioactive compounds is not fully controlled or known in the case of tea as compared to green tea extracts taken in pill form. For the latter, liver problems have been reported due to increased concentrations in a short period of time.
Despite this, the amount of green tea or how much it can be consumed can vary between individuals, type of green tea, as with other caffeinated beverages.
Green may offer important health benefits for some, however, caution should be taken for the risk of affecting those undertaking certain medications, caffeine sensitivity and any reaction that you feel is unusual in your body after drinking green tea.
Even though for some, drinking green tea can be beneficial, for some this may not be the case, as each person can react differently. If you have doubts about what to do it is best to ask your healthcare provider or dietitian for guidance, moreover there are differences between drinking green tea compared to consuming any sort of extract in which the dose, or amount of green tea, tends to be much higher.
- Musial C, Kuban-Jankowska A, Gorska-Ponikowska M. Beneficial Properties of Green Tea Catechins. Int J Mol Sci. 2020 Mar 4;21(5):1744. doi: 10.3390/ijms21051744. PMID: 32143309; PMCID: PMC7084675.
- Khan N, Mukhtar H. Tea polyphenols in promotion of human health. Nutrients. 2019 Jan;11(1):39.
- Johnson R, Bryant S, Huntley AL. Green tea and green tea catechin extracts: an overview of the clinical evidence. Maturitas. 2012;73:280-7.
- Yu F, Jin Z, Jiang H, Xiang C, Tang J, Li T, He J. Tea consumption and the risk of five major cancers: a dose–response meta-analysis of prospective studies. BMC Cancer. 2014 Dec;14(1):197.
- Yang YC, Lu FH, Wu JS, Wu CH, Chang CJ. The protective effect of habitual tea consumption on hypertension. Arch Intern Med. 2004;164:1534-40.
- Complete Guide to Green Tea – BornTea
- Hepatotoxicity of green tea: an update - PubMed (nih.gov)
- Green Tea for Cancer Prevention : AJN The American Journal of Nursing (lww.com)
- Green Tea - LiverTox - NCBI Bookshelf (nih.gov)
- Varieties of Green Tea (itoen-global.com)
- United States Pharmacopeia (USP) comprehensive review of the hepatotoxicity of green tea extracts - PubMed (nih.gov)
- Toxicological effects of Camellia sinensis (green tea): A review - PubMed (nih.gov)
- Tea | The Nutrition Source | Harvard T.H. Chan School of Public Health