Green tea: benefits, dosage, contraindications
Other name(s)
Camellia thea, Camellia theifera, Thea bohea, Thea sinensis, Thea viridis.
Scientific name(s)
Camellia sinensis
Family or group:
Plants
Active ingredients:
Catechins
L-Theanine
GABA
Caffeine
Epigallocatechin gallate
Indications
Scoring methodology
EFSA approval.
Warts ✪✪✪✪✪
A specific green tea extract ointment providing 150 mg of sinecatechins per gram of ointment, applied three times a day, is effective for external warts. In fact, it enables the removal of external genital and perianal warts in 24% to 60% of cases after 10-16 weeks of treatment.
Posologie
Topical: leaf
16 - weeks
Polyphenon E: a new treatment for external anogenital warts
Topical Polyphenon E in the treatment of external genital and perianal warts: a randomized controlled trial
Efficacy, safety and tolerability of green tea catechins in the treatment of external anogenital warts: a systematic review and meta-analysis
A randomized, double-blind, four-arm parallel-group, placebo-controlled Phase II/III study to investigate the clinical efficacy of two galenic formulations of Polyphenon E in the treatment of external genital warts
Cardiovascular diseases ✪✪✪✪✪
A large-scale epidemiological study in Japan found that consuming at least 3 to 5 cups of green tea per day is associated with a reduced risk of death from cardiovascular disease (stroke and heart disease) compared with consuming less than one cup per day. This effect is more pronounced in women than in men. Another epidemiological study in a population at high risk for coronary disease showed that drinking more than three cups of green tea per day is associated with a 46% reduction in the risk of coronary disease. A meta-analysis found that each additional cup of green tea consumed is associated with a 5% reduction in the risk of death from cardiovascular disease and a 3% reduction in the risk of cardiovascular events.
Posologie
Oral: leaf
3 - 10 cups
Relation between green tea consumption and the severity of coronary atherosclerosis among Japanese men and women
Inverse association of tea and flavonoid intakes with incident myocardial infarction: the Rotterdam Study
Black and green tea consumption and the risk of coronary artery disease: a meta-analysis
Associations between Green Tea Consumption and Coffee Consumption and the Prevalence of Coronary Artery Disease
Green tea consumption and mortality due to cardiovascular disease, cancer, and all causes in Japan: the Ohsaki study
Does tea affect cardiovascular disease? A meta-analysis
Tea consumption and mortality after acute myocardial infarction
Dose-Response Relation between Tea Consumption and Risk of Cardiovascular Disease and All-Cause Mortality: A Systematic Review and Meta-Analysis of Population-Based Studies
Hypercholesterolemia ✪✪✪✪✪
Clinical research in people with or without hyperlipidemia shows that consumption of green tea or green tea extract containing 150 - 2500 mg of catechins per day for 24 weeks reduces total cholesterol and LDL cholesterol compared with control. There is also preliminary evidence that taking a green tea extract containing 676 mg of catechins per day for 12 weeks reduces LDL cholesterol oxidation compared with placebo.
Posologie
Oral use: leaf
150 - 2500 mg
24 - weeks
catechins
Green tea consumption and risk of cardiovascular and ischemic related diseases: A meta-analysis
The effect of green tea on blood pressure and lipid profile: a systematic review and meta-analysis of randomized clinical trials
Effects of green tea extract combined with brisk walking on lipid profiles and the liver function in overweight and obese men: A randomized, double-blinded, placebo-control trial
Green tea catechins decrease total and low-density lipoprotein cholesterol: a systematic review and meta-analysis
Green and black tea for the primary prevention of cardiovascular disease
Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials
Effects of green tea catechin extract on serum lipids in postmenopausal women: a randomized, placebo-controlled clinical trial
Hypertension ✪✪✪✪✪
Epidemiological research in China shows that daily consumption of 120 to 599 ml of green tea is associated with a 46% reduced risk of developing hypertension. Consumption of more than 600 ml per day is associated with a 65% reduced risk. nnMeta-analyses in patients with or without hypertension, including overweight or obese adults, suggest that green tea reduces systolic and diastolic blood pressure by 1 to 3 mmHg. nn
Posologie
Oral: leaf
120 - 600 mL
The effects of regular consumption of green or black tea beverage on blood pressure in those with elevated blood pressure or hypertension: A systematic review and meta-analysis
Green and black tea for the primary prevention of cardiovascular disease
Effects of tea intake on blood pressure: a meta-analysis of randomized controlled trials
The effect of green tea on blood pressure and lipid profile: a systematic review and meta-analysis of randomized clinical trials
Green tea extract reduces blood pressure, inflammatory biomarkers, and oxidative stress and improves parameters associated with insulin resistance in obese, hypertensive patients
Effect of green tea supplementation on blood pressure: A systematic review and meta-analysis of randomized controlled trials
Effect of green tea supplementation on blood pressure among overweight and obese adults: a systematic review and meta-analysis
The effect of green tea and sour tea on blood pressure of patients with type 2 diabetes: a randomized clinical trial
Cold ✪✪✪✪✪
A randomized, double-blind, placebo-controlled trial found that the group that received green tea had a significantly lower incidence of influenza. The administered dose was six capsules of green tea extract per day (total catechins 378 mg/day and theanine 210 mg/day). nnAn observational study in Japan found that consuming 1 to 5 cups of green tea per day is associated with a decreased incidence of influenza. nn
Posologie
Oral: leaf
1 - 5 cups
Endometrial cancer ✪✪✪✪✪
Research meta-analyses have found that people who frequently drink green tea, usually more than once a day, have a 21% to 23% lower risk of developing endometrial cancer compared with those who never or rarely drink green tea. A meta-analysis also found that an increase in green tea consumption of one cup per day is associated with an 11% reduction in the risk of developing endometrial cancer. nn
Posologie
Oral: leaf
Ovarian cancer ✪✪✪✪✪
A meta-analysis suggests that a high green tea intake is associated with a 36% reduced risk of ovarian cancer compared with a low intake. Another study found that women who consume 2 cups of tea or more per day have a 46% lower risk of ovarian cancer compared with women who do not regularly consume tea. It also appears that a longer duration of consumption further reduces the risk of ovarian cancer. However, green tea does not appear to prevent ovarian cancer recurrence.
Posologie
By mouth: leaf
5 cups
Tea consumption and ovarian cancer risk: a case-control study in China
Green tea (Camellia sinensis) for the prevention of cancer
Meta-analysis of green tea drinking and the prevalence of gynecological tumors in women
Tea consumption and ovarian cancer risk in a population-based cohort
Cancer ✪✪✪✪✪
A Cochrane review concluded that there was conflicting evidence regarding the association between green tea consumption and reduced cancer risk, and suggested that the anticancer effect of green tea is not consistently proven. Other reviews and meta-analyses have suggested a trend toward protection in breast and prostate cancers and an improvement in survival rates in epithelial ovarian cancer. Another study found that increased green tea consumption was associated with an apparent delay in the onset of cancer and cancer-related death. The contradictory results among different studies may be due to confounding factors in different populations, and differences in the epigallocatechin gallate content of green teas.
Posologie
By mouth: leaf
5 cups
UV exposure ✪✪✪✪✪
Research conducted on human volunteers found that topical application of green tea to the skin half an hour before ultraviolet exposure protects against the development of sunburn and epidermal damage. The effect appears to be dose-dependent and strongest for the polyphenols epigallocatechin gallate and epicatechin gallate.
Posologie
Oral: leaf
Depression ✪✪✪✪✪
An epidemiological study suggests that consumption of at least four cups of green tea per day is associated with a 44% to 51% reduction in the prevalence of mild to severe depression compared to consumption of one cup or less per day.
Posologie
Oral: leaf
4 cups
Weight control ✪✪✪✪✪
Animal studies have shown that green tea consumption reduces food intake, decreases leptin levels and body weight, and increases thermogenesis. Clinical studies on the effects of green tea on weight loss have yielded mixed results; however, in some studies green tea is associated with moderate weight loss, a reduction in waist circumference, and improvements in metabolic parameters, and may be useful when combined with an exercise program. The wide variability of green teas, green tea extracts, and dosing protocols significantly hinders the pooling of results in meta-analyses.
Posologie
Oral: leaf
610 mg
12 weeks
catechins
Properties
Antioxidant
We think that the antioxidant effects of green tea and its constituent catechins explain some of its clinical effects, particularly its anti-inflammatory, anticancer, hepatoprotective, and cardiovascular benefits. In human studies, green tea and its catechins have been shown to protect against oxidative damage caused by exercise and smoking, as well as by general oxidative exposure. The antioxidant effects of green tea and its constituents may be related to their ability to scavenge free radicals, chelate redox-active transition metal ions, inhibit pro-oxidant enzymes, and induce antioxidant enzymes.
Usages associés
Anti-inflammatory
Catechins in green tea may have anti-inflammatory activity. Green tea–derived catechins inhibit cyclooxygenase-1 (COX-1). Green tea catechins may also inhibit leukotriene B4 production and 5-lipoxygenase activity. Epigallocatechin gallate (EGCG) inhibits COX-2 activity and interleukin (IL)-1 beta–induced nitric oxide synthase. EGCG and other green tea catechins may also reduce inflammation and protect cartilage by inhibiting the degradation of proteoglycans and collagen. In vitro, the anti-inflammatory activity of catechins may be due to inhibition of inflammatory cell and cytokine activity, or inhibition of proteins that promote the chemotaxis of these cells. In human research, the effects of green tea on inflammatory mediators are unclear. Studies show that green tea increases IL-6 levels, decreases TNF-alpha levels, but does not affect C-reactive protein levels.
Usages associés
Anticancer
The polyphenols in tea appear to have antimutagenic effects and may protect DNA. In humans, green tea reduces DNA damage in lymphocytes, probably by increasing the activity of the DNA repair enzyme oxoguanine glycosylase 1 (hOGG1) and the antioxidant enzyme heme oxygenase-1. Preliminary animal research suggests that epigallocatechin gallate (EGCG) may prevent the growth of new blood vessels (angiogenesis) in tumors. EGCG may also inhibit tumor cell proliferation by causing cell cycle arrest or apoptosis through the generation of reactive oxygen species. Green tea is also thought to be beneficial for preventing skin damage and cancer caused by ultraviolet (UV) rays because of the antioxidant effects of green tea polyphenols.
Usages associés
Digestive effect
The tannins contained in green tea may have antidiarrheal effects. The polyphenols in green tea could increase levels of lactobacilli and bifidobacteria and reduce the number of enterobacteria. On the other hand, the caffeine in green tea stimulates gastric acid secretion.
Lipid-lowering
In human studies, orally administered green tea appears to reduce total lipoproteins and low-density lipoproteins (LDL cholesterol). Some of these studies also suggest that green tea may reduce triglycerides and increase high-density lipoprotein (HDL cholesterol) levels. In animals, green tea has also led to decreases in total cholesterol, LDL cholesterol, and triglycerides.
Usages associés
Antibacterial
In vitro, green tea extract has moderate inhibitory effects on the growth of many types of pathogenic bacteria, including strains of Staphylococcus, Streptococcus, and Salmonella, Escherichia coli, and a strain of Corynebacterium suis. Another in vitro study demonstrated that green tea can significantly reduce the release of cytokines induced by bacterial endotoxins and may therefore reduce mortality from sepsis.
Antiviral
A number of in vitro studies have shown that epigallocatechin gallate (EGCG) strongly inhibits HIV replication and inhibits the attachment of HIV to T cells. Antiviral activity has also been identified against Epstein-Barr virus, herpes simplex virus 1, influenza A and B, rotavirus and enterovirus. In vitro research shows that green tea extract and EGCG inhibit human papillomavirus in human cervical cancer cells. The antiviral activity is probably due to interference with viral adsorption.
Usages associés
Cardiovascular
Studies in animals and humans reveal that green tea has multiple effects on the cardiovascular system, notably hypolipidemic, hypocholesterolemic, anti-inflammatory, antithrombotic, antioxidant, antihypertensive and anti-atherosclerotic effects, and it also shows a beneficial effect on endothelial function in healthy volunteers.
Usages associés
Neurological
In vivo studies have found a neuroprotective effect of epigallocatechin gallate (EGCG) on dopaminergic neurons, which is being investigated as a potential preventive treatment for Parkinson's disease. Two animal studies have shown that EGCG can prevent oxidation and apoptosis of neurons, and reduce beta-amyloid deposits. This may have implications for the development and progression of Alzheimer's disease. On the other hand, the caffeine contained in green tea stimulates the central nervous system. Possible mechanisms include blockade of adenosine receptors and inhibition of phosphodiesterase. By blocking adenosine receptors, caffeine is thought to increase the release of neurotransmitters such as dopamine. It has also been proposed that caffeine may decrease GABA and serotonin signaling.
Usages associés
Hypotensive
In vitro experiments show that green tea extracts inhibit angiotensin-converting enzyme (which catalyzes the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor). Animal experiments have also shown that a green tea extract protected against angiotensin II-induced hypertension. In humans, clinical research results remain contradictory. Some clinical studies suggest that taking green tea extract reduces blood pressure in hypertensive or normotensive patients.
Usages associés
Dermatological effect
Some evidence suggests that oral intake and the topical application of products containing green tea may improve skin elasticity and hydration. Evidence suggests that epigallocatechin gallate (EGCG) and epicatechin gallate (ECG) might inhibit 5-alpha-reductase and could potentially be useful in androgen-mediated skin disorders such as androgenetic alopecia, hirsutism, and acne. Green tea is also thought to be beneficial for preventing skin damage and cancer caused by ultraviolet (UV) rays due to the antioxidant effects of green tea polyphenols. Green tea polyphenolic extracts, particularly EGCG and epicatechin-3-gallate, appear to provide dose-dependent topical protection against UVA and UVB rays.
Usages associés
Hepatoprotective
Clinical research shows that green tea consumption is associated with decreased concentrations of liver enzymes, including aspartate aminotransferase and alanine transaminase, indicating a protective effect against liver disorders.
Safe dosage
Adult: 3 cups - 10 cups (tea/infusion/tisane)
The dose varies depending on the indication. Some research suggests that 8 to 10 cups of green tea per day are required, while other studies indicate that only 3 to 5 cups of green tea per day are necessary. The dose is also likely to depend on the quality of the green tea and the concentration of catechins in the preparation. One cup of tea provides about 50 mg of caffeine and 80 to 100 mg of polyphenols.
Interactions
Médicaments
Adenosine: moderate interaction
Theoretically, green tea could reduce the vasodilatory effects of adenosine. The caffeine in green tea is a competitive inhibitor of adenosine at the cellular level.
Amphetamines: strong interaction
Theoretically, the caffeine in green tea could increase the risk of additive effects on the central nervous system.
Antidiabetic: weak interaction
Theoretically, concomitant use of green tea and antidiabetic medications could interfere with blood sugar control due to the caffeine in green tea. Reports indicate that green tea and/or caffeine may increase or decrease blood glucose.
Cimetidine: moderate interaction
Concurrent use could increase the adverse effects of the caffeine in green tea. Cimetidine can reduce caffeine clearance by 31% to 42%.
Clozapine: moderate interaction
Concurrent administration of green tea and clozapine could theoretically cause an acute exacerbation of psychotic symptoms due to the caffeine present in green tea. Caffeine can increase the effects and toxicity of clozapine.
Cocaine: strong interaction
Theoretically, the caffeine in green tea could increase the risk of additive effects on the central nervous system.
Oral contraceptives: moderate interaction
Concurrent use of green tea and oral contraceptives could increase the adverse effects of the caffeine in green tea. Oral contraceptives can reduce caffeine clearance by 40% to 65%.
Nadolol: strong interaction
Preliminary clinical research shows that green tea consumption reduces plasma concentrations of nadolol and significantly reduces its antihypertensive effect.
Atorvastatin: strong interaction
In healthy humans, taking green tea extract at doses of 300 mg or 600 mg with atorvastatin reduces plasma atorvastatin levels by about 24%. Atorvastatin elimination is not affected.
Quinolone: moderate interaction
Green tea contains caffeine. Quinolones (also called fluoroquinolones) can decrease caffeine clearance by inhibiting the cytochrome P450 1A2 enzyme.
Plantes ou autres actifs
Green tea: moderate interaction
Green tea appears to reduce the absorption of non-heme iron from foods.
Precautions
Pregnant women: use with caution
Usual dietary intakes appear to be safe. However, excessive use is not recommended because of the caffeine content of green tea. Pregnant women should limit their caffeine intake to less than 200 mg per day, as it crosses into the fetal bloodstream.
Breastfeeding women: use with caution
Usual dietary intakes appear to be safe. However, excessive use is not recommended because of the caffeine content of green tea. Breastfeeding women should limit their caffeine intake to less than 200 mg per day, as it passes into breast milk.
High blood pressure: avoid
Green tea contains caffeine and can temporarily increase blood pressure. nn
Liver disorders: avoid
Green tea extract supplements have been associated with several cases of hepatotoxicity. nn
Osteoporosis: avoid
Green tea contains caffeine which can increase urinary calcium excretion. nn
Anemia: avoid
Green tea may worsen anemia in people with iron deficiency. nn
Anxiety: use with caution
Taking more than 400 mg of caffeine per day, as found in about 8 cups of green tea, has been shown to worsen anxiety disorders. nn
Heart disorders: avoid
Green tea contains caffeine, which could cause cardiac arrhythmias in sensitive individuals. nn
Sleep disorders: avoid
Green tea contains caffeine that can worsen insomnia. nn
Type 2 diabetes: avoid
People with diabetes should avoid consuming large amounts of tea or caffeine, as the latter appears to cause an increase in blood sugar, especially late in the day.nn
