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Green Tea Leaves Extract

Also known as: Camellia sinensis, Green tea, Green tea leaves extract

Overview

Green tea extract is derived from the leaves of the *Camellia sinensis* plant, the same plant used to produce black and oolong tea. Unlike black tea, green tea leaves are steamed or pan-fried to prevent fermentation, preserving their high content of beneficial compounds called catechins. The most abundant and well-researched catechin in green tea is epigallocatechin gallate (EGCG). Green tea extract is commonly used as a dietary supplement due to its potential health benefits, including supporting cardiovascular health, aiding in weight management, and providing antioxidant protection. It is available in various forms, including capsules, tablets, and powders, offering a concentrated source of these bioactive compounds. Research on green tea extract is extensive, with numerous studies exploring its effects on various aspects of health.

Benefits

Green tea extract (GTE) has shown promise in improving cardiovascular health. A meta-analysis indicated that GTE supplementation significantly reduced total cholesterol, LDL cholesterol, fasting blood sugar, HbA1c, and diastolic blood pressure, while increasing HDL cholesterol. These benefits were more pronounced in males, individuals with a BMI between 25-29.9 kg/m², and those without a history of type 2 diabetes. However, another meta-analysis found no significant effect of green tea or GTE on fasting plasma glucose, fasting serum insulin, 2-h plasma glucose in the oral glucose tolerance test (OGTT), HbA1c, or the homeostasis model of insulin resistance (HOMA(IR)) index in populations at risk of type 2 diabetes mellitus (T2DM). Evidence regarding the effectiveness of green tea extract for post-exercise muscle pain and recovery is limited and inconsistent, requiring further high-quality studies.

How it works

Green tea catechins, especially EGCG, exert their effects through multiple biological pathways. These include antioxidant activity, which helps neutralize harmful free radicals, and anti-inflammatory effects, which can reduce inflammation throughout the body. EGCG also modulates lipid metabolism and blood pressure regulation, contributing to cardiovascular health. It interacts with various body systems, including the cardiovascular system, metabolic pathways, and the antioxidant defense system. EGCG targets molecular pathways involved in lipid metabolism (e.g., LDL receptors), blood pressure regulation (e.g., angiotensin-converting enzyme), and antioxidant defense (e.g., glutathione S-transferase). The bioavailability of green tea catechins is relatively low, but the presence of other compounds in green tea may enhance EGCG absorption.

Side effects

Green tea extract is generally considered safe when consumed in moderate amounts. Common side effects are not consistently reported across studies, but some individuals may experience gastrointestinal disturbances such as nausea and diarrhea. Rare cases of liver toxicity have been associated with high doses of green tea extract, although these are uncommon and may be related to other factors. Green tea extract may interact with certain medications, such as blood thinners and some antidepressants, due to its catechin content. Caution is advised for individuals with liver disease or those taking medications that could interact with green tea catechins. Pregnant or breastfeeding women should consult healthcare providers before using green tea extract due to limited safety data in these populations.

Dosage

While the minimum effective dose for cardiovascular benefits is not definitively established, studies have explored doses ranging from 250 mg to 1000 mg per day of green tea extract. For cardiovascular health, doses of 500-1000 mg per day of green tea extract, containing approximately 200-400 mg of EGCG, have shown significant benefits. There is no established maximum safe dose, but high doses (over 2000 mg/day) may increase the risk of side effects such as liver toxicity. It is generally advised to take the supplement with meals to enhance bioavailability. Capsules or tablets containing standardized green tea extract are commonly used. The presence of other nutrients, such as vitamin C, may enhance the bioavailability of green tea catechins.

FAQs

Is green tea extract safe?

Green tea extract is generally safe, but high doses and interactions with certain medications should be considered. Individuals with liver issues or those on blood thinners should exercise caution.

When should I take green tea extract?

There is no specific timing recommended, but taking it with meals may help enhance absorption. Consistency is key to experiencing potential benefits over time.

What results can I expect from taking green tea extract?

Consistent supplementation over several weeks may lead to reductions in cardiovascular risk factors. However, it's not a substitute for medical treatment and should complement a healthy lifestyle.

Can green tea extract replace my medications?

No, green tea extract is not a substitute for medical treatment. It should be used in conjunction with a healthy lifestyle and under the guidance of a healthcare professional.

Research Sources

https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2022.1084455/full – This systematic review and meta-analysis of 55 RCTs found that green tea extract supplementation significantly reduced total cholesterol, LDL cholesterol, fasting blood sugar, HbA1c, and diastolic blood pressure, while increasing HDL cholesterol. The benefits were more significant with longer durations of supplementation (≥ 12 weeks) and in specific subgroups, such as males and individuals with a BMI between 25-29.9 kg/m².
https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD005004.pub3/references – This Cochrane review assesses the effects of green tea for the treatment of rheumatoid arthritis. While the full text requires a subscription, the reference list provides valuable context on the types of studies considered in evaluating green tea's anti-inflammatory potential, highlighting the need for rigorous, controlled trials to determine efficacy.
https://pubmed.ncbi.nlm.nih.gov/34966132/ – This systematic review examined the effects of green tea extract on post-exercise muscle pain and recovery. The review concluded that the evidence is inconsistent and that more high-quality studies are needed to determine the efficacy of green tea extract in this area, highlighting the need for further research with robust methodologies.
https://pubmed.ncbi.nlm.nih.gov/24206044/ – This meta-analysis of 7 RCTs involving 510 participants found no significant effect of green tea or green tea extract on fasting plasma glucose, fasting serum insulin, OGTT-2 h glucose, HbA1c, or HOMA(IR) index in populations at risk of type 2 diabetes mellitus. The study suggests that green tea may not be effective for improving glycemic control in at-risk populations.
https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD009934.pub2/full – This Cochrane review investigates the effectiveness of green tea for preventing cardiovascular disease. The review assesses multiple trials and provides a comprehensive overview of the evidence, concluding that more high-quality research is needed to fully determine the impact of green tea consumption on cardiovascular outcomes.