Green Tea (GT)

Tea is the most widely consumed beverage in the world, second only to water. The three kinds of true tea—green, black, and oolong—are all derived from the Camellia sinensis plant. At harvest, tea leaves contain high levels of active constituents but after harvest these constituents are rapidly oxidized  to a complex mixture of other derivatives that are responsible for the characteristic color of oolong and black tea. Green tea (GT), however, is produced by heat-treating leaves soon after harvest, thereby preserving these constituents from oxidation.


The constituents in green tea include powerful antioxidants that offer many health benefits. In addition, green tea constituents inhibit COMT, an enzyme that metabolizes various neurotransmitters including dopamine and noradrenaline. As a result of these actions, it is believed that ingesting green tea may be useful in conditions including cardiovascular health, anxiety and depression, arthritis, weight loss, fatty liver disease and possibly breast cancer in select individuals.


For a list of downloadable journal publications reviewing the many potential health benefits of green tea, please scroll to the bottom of this page.


See also:


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Green Tea phytosome


Green Tea


Green Tea vs Black or Oolong Tea

Green tea catechins, including (-)-epicatechin (EC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin (EGC) and (-)-epigallocatechin gallate (EGCG), are oxidized and dimerized during the manufacture of black tea and oolong tea to form orange-red pigments, theaflavins.  Studies indicate tha the antioxidant capacity of theaflavins meet or exceed those of green tea catechins. However, it is not evident that the weight loss benefit of the theaflavins matches those of green tea catechins.


Green Tea – Preparatiom, Dosing and Effect

Tea is the most widely consumed beverage in the world, second only to water. The three kinds of true tea—green, black, and oolong—are all derived from the Camellia sinensis plant. At harvest tea leaves contain high levels of catechins, a particular class of polyphenols. After harvest catechins may be rapidly converted by enzymatic oxidation to a complex mixture of other derivatives, thearubigins and theaflavins, responsible for the characteristic color of oolong and black tea. Green tea (GT), however, is produced by heat-treating leaves soon after harvest, thereby preserving the catechins from oxidation.


The amount of catechins in a cup of GT is highly variable, depending on the precise type of tea, the ratio of dry tea to water and on the time and temperature that the leaves are infused before consumption. Catechins constitute about 14 to 33% of the dry green tea leaf weight. An average serving of 250 ml of GT may contains as little as 10mg (ready-to-drink versions)  and 200 mg of catechins (brewed, loose leaf). In addition, GT contains a variable amount (typically around 30 mg/serving) of caffeine. The addition of milk to the tea does not seem to affect the absorption of the catechins.


To get the most catechins from your cup of green tea:

  1. Quality counts. Avoid mass market brands and choose a specialist brand from Japan or China.
  2. Choose either powdered or loose leaf green tea
  3. Whether you choose green or white tea doesn’t matter – they both have similar antioxidant potential and ECGC levels. But oolong and black tea have similar antioxidant potential  but have significantly less catechins.
  4. Brew your tea in boiling hot water for 3 to 4 minutes.
  5. Drink your tea or take your supplements on an empty stomach – absorption may be as much as 3-4x higher.

Consumption of tea catechins (375–612 mg/d from oolong tea, green tea, or green tea extract) with caffeine (150– 270 mg/d) may modestly (3–4%) increase 24-h energy expenditure. One study did not show enhanced 24-h energy expenditure or fat oxidation with EGCG at doses of 270, 600, 900, and 1200 mg, each with 600 mg caffeine. The effects of caffeine and catechins may be additive to a point, but the dose of caffeine employed by these investigators may have been high enough that catechins could not enhance the responses.

Green Tea – Toxicity
There have been reports of rare liver toxicity associasted with the use of green tea/ECCG supplements, although most cases were associated with multi-nutrient supplements and a causal effect for green tea is uncertain. To be safe, do not exceed recommended doses and discontinue supplements if any side effects are experienced.

Drug Interactions with Green Tea

While the clinical significance has not yet been established, green tea has been shown to inhibit P-gp, a transporter that affects blood levels and central nervous system levels of certain drugs. As a
result of this inhibition, it may be possible that green tea can decrease blood levels but at the same time increase central nervous levels of fentanyl, morphine, methadone and possibly oxycodone. This could result in either increased or decreased therapeutic effect and/or side effects. When taking green tea while also taking these medications, caution should be emphasized by monitoring for changes in responsiveness to the medications and it may be necessary to reduce the dose of these medications to avoid side effects.


Green Tea – Genetics and COMT activity

A recent study evaluated the role of genetic variability of COMT activity and the effect of  green tea catechins on energy expenditure and fat oxidation. Thermogenesis, the calorie-burning process of producing body heat, is regulated by norepinephrine and norepinephrine is metabolized by COMT. Inhibiting COMT prolongs norepinephrine-driven thermogenesis causing more energy expenditure and fat to be oxidized and more calories to be burned, ultimately contributing to improved weight loss. The catechin components of green tea are strong inhibitors of COMT. The greater an individual’s COMT activity, the greater the impact and benefit green tea will have on fat oxidation and weight loss. Genetic testing allows prediction of an individual’s COMT activity and can therefore predict benefit of green tea as a weight loss supplement.


Green Tea – Visceral Fat

The sympathetic nervous system is thought to play a role in regional differences in mobilization of lipid from adipose depots. Therefore, it is possible that catechins, by enhancing sympathetic effects, might have differential influences on lipid storage in various fat depots. Findings from studies in animals suggest that mesenteric and hepatic (visceral) fat accumulation are markedly reduced by catechin (and caffeine) feeding. Research  supports the belief that catechin consumption may enhance reductions in visceral fat.


Greater visceral fat loss is of particular interest because excess visceral fat is an important risk factor for cardiovascular disease. Intra-abdominal (visceral) fat has the highest rate of triglyceride turnover and excess visceral adiposity is the most closely related to metabolic disturbances, particularly insulin resistance and hypertriglyceridemia. Upper body subcutaneous fat is the next most active and lower body subcutaneous fat has the lowest rate of triglycerides turnover; therefore, excess lower body subcutaneous fat is the least metabolically adverse.

Commercial Products

Because there are many variables in the preparation of green tea that affect the quality and quantity of active constituents available, commercial products have been developed that  provide reliable, measured levels of the active constituents. Most studies evaluating the health benefits of green tea constituents are performed using supplements rather than tea in order to control dosing and maintain consistency to allow for predictable conclusions.


In addition to the fact that studies support the health benefits of supplements containing green tea constituents, there is the added convenience of using a supplement rather than preparing tea leading to a greater ease of adherence to regular use.


Because the natural constituents of green tea do not always absorb well from the gut, supplements may include phytosomal components that enhance absorption and improve likelihood of benefit.


Green Tea Phytosome – Thorne

Greenselect® Phytosome – a well-absorbed complex of green tea polyphenols and phosphatidylcholine*

The antioxidant, liver protective, and metabolic benefits of green tea without the caffeine*

Provides thermogenic (fat burning) effects*

Optimum bioavailability from phytosome preparation*



One Capsule Contains:
Green Tea Phytosome* (leaf) (Camellia sinensis extract (leaf) / Phosphatidylcholine complex) 250 mg.

Other Ingredients:

High and low viscosity hydroxypropyl methylcellulose and CalciumCitrateLaurate (Time-Sorb*), Hypromellose (derived from cellulose) capsule, Leucine, Silicon Dioxide.
*Green Tea Phytosome complexed with Time-Sorb®, a time-release matrix.
This product uses Indena S.p.A.’s green tea phytosome (Greenselect®). Greenselect is a registered trademark of Indena S.p.A.
Contains ingredient derived from soy (phytosome).

Product Description

A study on healthy volunteers compared absorption of a single 400-mg dose of green tea polyphenols as non-complexed standardized extract Greenselect or as the same extract complexed with phosphatidylcholine – Greenselect Phytosome. Peak blood concentration of EGCG from the phytosome, measured over a period of six hours, was approximately double that of the non-complexed green tea extract.*


Green tea polyphenols are powerful antioxidants due to their particular flavonoid structures, and their glutathione-sparing activity has been well documented.* Green tea polyphenols also help maintain the body’s normal inflammatory response to oxidative stressors.*


Green tea has a thermogenic effect.* Extracts of EGCG increase energy expenditure and fat oxidation, thus essentially burning calories.* Greenselect Phytosome was tested in obese subjects (n=100) of both genders on a low-caloric diet; 50 subjects were assigned to the green tea extract plus the low-calorie diet, while the other 50 subjects followed the low-calorie diet only. After 90 days of treatment, significantly greater improvement in weight and body mass index was observed in the Gree
nselect P
hytosome group compared to the diet-only group.*


Human studies of green tea’s weight management properties resulted in greater calorie burning by individuals taking the extract.* Although some of the effects of green tea extract have been attributed to the caffeine content, a study found increased metabolic rate and greater fat metabolism in study subjects taking green tea extract compared to those taking a placebo, even though the green tea extract did not contain caffeine.*


* These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

Reference Publications

Green tea –  Overviews

  1. Green tea | University of Maryland Medical Center
  3. Health-promoting effects of green tea – 2012
  4. Antioxidant effects of green tea – 2011
  5. New insights into the mechanisms of polyphenols beyond antioxidant properties – lessons from the green tea polyphenol, epigallocatechin 3-gallate -2014


  Green tea – Anxiety and Depression

  1. Novel Therapeutic Targets in Depression and Anxiety – Antioxidants as a Candidate Treatment
  2. Anxiolytic properties of green tea polyphenol (-)-epigallocatechin gallate (EGCG). – PubMed – NCBI
  3. Epigallocatechin gallate attenuates acute stress responses through GABAergic system in the brain – 2006
  4. Psychiatric Disorders and Polyphenols – Can They Be Helpful in Therapy? – 2015

Green tea –  Bioavailability

  1. Bioavailability and activity of phytosome complexes from botanical polyphenols – the silymarin, curcumin, green tea, and grape seed extracts – 2009
  2. Food Inhibits the Oral Bioavailability of the Major Green Tea Antioxidant Epigallocatechin Gallate in Humans – 2015


Green tea –  Black Tea, Oolong Tea

  1. Green Tea, Black Tea, and Oolong Tea Polyphenols Reduce Visceral Fat and Inflammation in Mice Fed High-Fat, High-Sucrose Obesogenic Diets – 2014
  2. Theaflavins in black tea and catechins in green tea are equally effective antioxidants. – Sunphenon


Green tea – COMT

  1. The Role of Catechol-O-Methyl Transferase Val(108:158)Met Polymorphism (rs4680) in the Effect of Green Tea on Resting Energy Expenditure and Fat Oxidation – 2014
  2. Human Catechol-O-Methyltransferase Haplotypes Modulate Protein Expression by Altering mRNA Secondary Structure – 2006
  3. Enzymology of Methylation of Tea Catechins and Inhibition of COMT by Epigallocatechin Galleate
  4. The impact of the catechol-O-methyltransferase genotype on vascular function and blood pressure after acute green tea ingestion. – PubMed – NCBI


Green tea – COVID

  1. < a href=” CG-a-Green-Tea-Catechin-as-a-Potential-Therapeutic-Agent-for-Symptomatic-and-Asymptomatic-SARS-CoV-2-Infection-2021.pdf”>EGCG, a Green Tea Catechin, as a Potential Therapeutic Agent for Symptomatic and Asymptomatic SARS-CoV-2 Infection – 2021

 Green tea – Dosing

  1. Hack Your Tea – How To Get 5 Times More Out Of A Cup Of Green Tea

Green teaDrug Interactions

  1. Overview of P-glycoprotein inhibitors – a rational outlook – 2012
  2. Emerging Significance of Flavonoids as P-Glycoprotein Inhibitors in Cancer Chemotherapy – 2009
  3. Herbal modulation of P-glycoprotein. [Drug Metab Rev. 2004] – PubMed – NCBI


 Green tea – Fatty Liver (NAFLD)

  1. Green Tea Extract Rich in Epigallocatechin-3-Gallate Prevents Fatty Liver by AMPK Activation via LKB1 in Mice Fed a High-Fat Diet – 2015

Green tea – Metabolic Syndrome, Heart Disease

  1. Epigallocatechin Gallate – A Review of Its Beneficial Properties to Prevent Metabolic Syndrome – 2015
  2. Green and black tea for the primary prevention of cardiovascular disease. – PubMed – NCBI

Green tea – Nanoformulations

  1. Nanoencapsulation Enhances Epigallocatechin-3-Gallate Stability and Its Anti-atherogenic Bioactivities in Macrophages – 2014
  2. Greenselect Phytosome as an adjunct to a low-calorie diet for treatment of obesity – a clinical trial – 2009

Green tea – Osteoarthritis

  1. Green tea polyphenol treatment is chondroprotective, anti-inflammatory and palliative in a mouse posttraumatic osteoarthritis model – 2014


Green tea – Quercetin

  1. Quercetin increased bioavailability and decreased methylation of green tea polyphenols in vitro and in vivo


Green tea – Toxicity

  1.  Hepatotoxicity of green tea: an update. – PubMed – NCBI

Green tea – Visceral Fat

  1. Green Tea Catechin Consumption Enhances Exercise-Induced Abdominal Fat Loss in Overweight and Obese Adults – 2009
  2. A Green Tea Extract High in Catechins Reduces Body Fat and Cardiovascular Risks in Humans – 2007
  3. Effects of Catechin Enriched Green Tea on Body Composition – 2010

Green tea – Uterine Fibroids

  1. Treatment of symptomatic uterine fibroids with green tea extract – 2013

Green tea – Wt Loss 

  1. Green tea for weight loss and weight maintenance in overweight or obese adults. – PubMed – NCBI
  2. The Role of Catechol-O-Methyl Transferase Val(108:158)Met Polymorphism (rs4680) in the Effect of Green Tea on Resting Energy Expenditure and Fat Oxidation – 2014
  3. Effects of Catechin Enriched Green Tea on Body Composition – 2010
  4. Effect of a Thermogenic Beverage on 24-Hour Energ
    y Metabolism in Humans – 2007
  5. The putative effects of green tea on body fat: an evaluation of the evidence and a review of the potential mechanisms. – PubMed – NCBI

Green tea – Breast Cancer

  1. Tea Intake, COMT Genotype, and Breast Cancer in Asian-American Women

Emphasis on Education


Accurate Clinic promotes patient education as the foundation of it’s medical care. In Dr. Ehlenberger’s integrative approach to patient care, including conventional and complementary and alternative medical (CAM) treatments, he may encourage or provide advice about the use of supplements. However, the specifics of choice of supplement, dosing and duration of treatment should be individualized through discussion with Dr. Ehlenberger. The following information and reference articles are presented to provide the reader with some of the latest research to facilitate evidence-based, informed decisions regarding the use of conventional as well as CAM treatments.


For medical-legal reasons, access to these links is limited to patients enrolled in an Accurate Clinic medical program.


Should you wish more information regarding any of the subjects listed – or not listed –  here, please contact Dr. Ehlenberger. He has literally thousands of published articles to share on hundreds of topics associated with pain management, weight loss, nutrition, addiction recovery and emergency medicine. It would take years for you to read them, as it did him.


For more information, please contact Accurate Clinic.


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