Grean Tea extract
Also known as: Green tea extract, GTE, matcha, epigallocatechin gallate, EGCG, epicatechin, epicatechin gallate, epigallocatechin, Camellia sinensis extract
Overview
Green tea extract (GTE) is a concentrated botanical supplement derived from the leaves of Camellia sinensis, the plant from which green tea is made. It is rich in polyphenols, particularly catechins like epigallocatechin gallate (EGCG), which is considered its primary bioactive compound. GTE is widely used for its antioxidant properties and is commonly supplemented for weight management, cardiovascular health, and to combat oxidative stress. Research on GTE is extensive, with numerous randomized controlled trials and meta-analyses supporting its efficacy for body composition and cardiovascular markers, though evidence for cognitive benefits remains mixed or inconclusive. It is available in various forms, including capsules, powders, and as matcha, a powdered green tea variant.
Benefits
Green tea extract offers several evidence-based benefits, primarily due to its high catechin content. A meta-analysis of 59 randomized controlled trials (n=3802) demonstrated that GTE supplementation significantly reduced body mass (BM), body mass index (BMI), and body fat percentage (BFP) (p<0.05), with some dose- and duration-dependent effects on fat mass (FM) and waist circumference (WC). It also significantly increased total antioxidant capacity (TAC) and reduced malondialdehyde (MDA), markers of oxidative stress, particularly within 12 weeks of supplementation. For cardiovascular health, a systematic review and meta-analysis reported modest but significant reductions in systolic blood pressure (~−1.98 mmHg) and improvements in lipid and glycemic profiles. GTE has also been shown to increase adiponectin, an obesity-related hormone. While these benefits are statistically significant, the magnitude of effect on body weight and blood pressure is modest. Antioxidant benefits may be more pronounced in men, while weight and metabolic benefits are observed across adults with overweight or obesity. Cognitive function benefits, however, are not statistically significant at typical consumption levels.
How it works
The primary mechanism of action for green tea extract involves its catechin content, especially EGCG. These catechins act as potent antioxidants by scavenging free radicals and upregulating the body's endogenous antioxidant enzymes, thereby reducing oxidative stress. GTE interacts with various body systems by modulating lipid metabolism, enhancing fat oxidation, and improving endothelial function, which contributes to cardiovascular health. At a molecular level, EGCG is known to inhibit catechol-O-methyltransferase (COMT), an enzyme that degrades catecholamines, potentially prolonging their thermogenic effects. It also affects the AMP-activated protein kinase (AMPK) pathway, which plays a role in energy homeostasis, and modulates inflammatory cytokines, contributing to its anti-inflammatory properties. Catechins have moderate oral bioavailability, which can be influenced by formulation and food intake.
Side effects
Green tea extract is generally considered safe when consumed within recommended dosages, with adverse effects being rare. The most common side effect reported is mild gastrointestinal discomfort, which may include stomach upset or nausea. Less common side effects (1-5% frequency) can include headache and dizziness. In rare instances (<1%), liver toxicity has been reported, typically associated with very high doses or highly concentrated extracts, particularly when taken on an empty stomach, and is not common with standard supplementation. Individuals with pre-existing liver conditions should exercise caution. GTE can interact with certain medications; its caffeine content may interact with stimulant medications, and it may potentiate the effects of blood thinners like warfarin. Contraindications include individuals with liver disease or those highly sensitive to caffeine. Pregnant and breastfeeding women should avoid high-dose extracts due to insufficient safety data.
Dosage
The minimum effective dose for green tea extract varies, but studies commonly use doses around 300–500 mg of total catechins per day. Optimal dosage ranges typically fall between 300–800 mg/day of catechins, often standardized to EGCG content. The maximum safe dose is generally considered up to 800 mg EGCG per day for most adults; higher doses should only be taken under medical supervision due to potential risks. GTE can be taken with or without food, though absorption may be improved on an empty stomach, which could also increase the likelihood of gastrointestinal side effects. Extracts standardized for catechin content are preferred for consistent dosing. While no specific cofactors are strictly required, some formulations may include vitamin C or piperine to enhance bioavailability. Timing is flexible, with some individuals preferring to take it in the morning or before exercise.
FAQs
Is green tea extract effective for weight loss?
Yes, meta-analyses of randomized controlled trials have shown modest but statistically significant reductions in body weight, BMI, and body fat percentage with green tea extract supplementation.
Is it safe for long-term use?
Generally, green tea extract is considered safe for long-term use at recommended dosages. However, very high doses should be avoided without medical advice due to potential liver toxicity.
Does it improve cognitive function?
Current scientific evidence does not consistently support significant cognitive benefits in humans at typical green tea extract consumption levels.
When is the best time to take green tea extract?
The timing is flexible; it can be taken with or without food. Some prefer taking it in the morning or before exercise. Taking it on an empty stomach might enhance absorption but could increase GI side effects.
Does the caffeine content in green tea extract matter?
Yes, the caffeine content contributes to stimulant effects and can cause side effects like jitters or sleep disturbances in caffeine-sensitive individuals. Decaffeinated versions are available.
Research Sources
- https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/effects-of-green-tea-extract-supplementation-on-body-composition-obesityrelated-hormones-and-oxidative-stress-markers-a-gradeassessed-systematic-review-and-doseresponse-metaanalysis-of-randomised-controlled-trials/5F7DCFF04BE51796D39A6CC5B0A3089A – This high-quality systematic review and meta-analysis of 59 RCTs (n=3802) found that green tea extract significantly reduced body mass, BMI, and body fat percentage. It also increased total antioxidant capacity and adiponectin while reducing malondialdehyde, indicating benefits for body composition and oxidative stress markers.
- https://pubmed.ncbi.nlm.nih.gov/38031409/ – This PubMed entry corresponds to the same Hadi et al. (2023) study, confirming its findings on the effects of green tea extract supplementation on body composition, obesity-related hormones, and oxidative stress markers. It highlights the robust methodology, including GRADE assessment, used to evaluate the evidence.
- https://www.nature.com/articles/srep06251 – This meta-analysis of 13 RCTs investigated the effect of green tea on blood pressure, reporting a modest but significant reduction in systolic blood pressure by approximately 1.98 mmHg. While the effect size is small, it suggests a potential benefit for cardiovascular health at a population level, despite some variability in study quality.
- https://www.neurology.org/doi/10.1212/WNL.0000000000211496 – This systematic review focused on the cognitive effects of matcha green tea in humans. It concluded that there was no statistically significant improvement in cognitive function observed at typical consumption levels, suggesting that cognitive benefits remain unproven for green tea extract in human populations.
- https://pmc.ncbi.nlm.nih.gov/articles/PMC9871939/ – This systematic review and meta-analysis examined the impact of green tea on cardiovascular risk factors. It found improvements in lipid and glycemic profiles, indicating a beneficial role for green tea in managing cardiovascular health, although it noted variability in study designs and limited long-term data.
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