Le thé vert est une boisson quotidienne agréable, dotée de quelques effets modestes et bien documentés. Bu régulièrement, il abaisse un peu le cholestérol total et la pression artérielle systolique, tous deux mesurés dans des essais courts. Sa qualité la plus distinctive est l'association L-théanine et caféine présente dans la feuille, qui procure une vigilance calme.
Les réputations plus grandes — cancer, perte de poids, glycémie — reposent sur des bases plus fragiles. Un produit comporte un risque réel : l'extrait concentré de thé vert a provoqué des lésions hépatiques à fortes doses. Le matcha utilise la feuille entière broyée, il frappe donc plus fort.
Findings & Outcomes
What It Is
Green tea is the leaf of Camellia sinensis, the same plant as black tea. It is dried without oxidation, so it keeps more of its pale-green catechins. The chief one is EGCG, the compound most health research tracks. The leaf also carries caffeine and L-theanine, the amino acid behind its steady, calm lift. A mug delivers perhaps 50 to 100 mg of catechins.
Matcha is the whole leaf, stone-ground to powder and whisked into water, so a serving carries more catechins and more caffeine than a steeped, strained cup. Concentrated extract capsules pull the catechins out of the drink; one can hold several hundred milligrams of EGCG in a single dose.
What It Does
Pooled across randomized trials, daily green tea lowers total cholesterol by about 7 mg/dL and systolic blood pressure by about 2 mmHg. The drop is larger where the starting numbers were high, and both come from short trials. Weight loss, movement, and whole food move these same markers far more, so tea is a modest addition on top of the real work.
The calm-alertness effect is quicker and just as measurable as the lipid change, clearest in the first hour or two after a cup. The bigger reputations rest on weaker ground: the cancer, weight-loss, and blood-sugar effects are small or unconfirmed.
The Research & Studies
Everything here is based on the research we have collected and checked, sorted into groups and ordered with the strongest evidence first. Click any claim to open the studies behind it.
Cholesterol And Lipids
Total cholesterol down about 7 mg/dL, LDL down 2 mg/dL, HDL unchanged
Drinking green tea regularly nudged total cholesterol down by a small amount, with a smaller drop in LDL and no change in the good HDL.
Meta-analysis of 14 RCTs (Zheng 2011), pooling green tea beverages and extracts; effects were consistent across catechin dose, study duration and health status, and heterogeneity was low. A separate meta-analysis of 20 RCTs (Onakpoya 2014) found similar reductions in total and LDL cholesterol and judged the lipid effect moderate.
The studies · 2
Zheng 2011, Am J Clin Nutr · Am J Clin Nutr
Onakpoya 2014, Nutr Metab Cardiovasc Dis · Nutr Metab Cardiovasc Dis
Counts once: this finding and 1 other here come from the same source, so they are one body of evidence, not separate confirmations.
Heart And Vascular
Pression artérielle systolique en baisse d'environ 2 mmHg
Boire du thé vert a fait baisser la tension artérielle d'environ deux points en moyenne, un effet faible mais constant.
Revue systématique et méta-analyse de 20 ECR (Onakpoya 2014). Les effets indésirables rapportés dans les essais inclus comprenaient éruption cutanée, élévation de la pression artérielle et gêne abdominale. Les auteurs ont appelé à des essais indépendants à plus long terme.
The study · 1
Onakpoya 2014, Nutr Metab Cardiovasc Dis · Nutr Metab Cardiovasc Dis
Counts once: this finding and 1 other here come from the same source, so they are one body of evidence, not separate confirmations.
Longevity And Mortality
Mortalité toutes causes et par maladie cardiaque plus faible chez les plus grandes consommatrices (femmes HR 0.77 et 0.69), aucun lien avec la mortalité par cancer
Dans une large population japonaise, les personnes qui buvaient le plus de thé vert avaient moins de risque de mourir de maladie cardiaque et de toute cause, mais pas moins de risque de mourir d'un cancer.
Cohorte prospective suivie jusqu'à 11 ans pour la mortalité toutes causes et jusqu'à 7 ans pour la mortalité par cause spécifique (Kuriyama 2006). Les associations inverses étaient plus fortes chez les femmes. Il s'agit d'une association observationnelle, non d'un essai, et la consommation de thé vert au Japon est corrélée à d'autres habitudes.
The study · 1
Kuriyama 2006, JAMA · JAMA
Weight And Fat Loss
Le thé vert n'a pas produit de perte de poids significative (-0.09 lb (-0.04 kg) en dehors du Japon)
Le thé vert entraîne très peu de perte de poids ; dans les essais non japonais plus comparables, le changement moyen était pratiquement nul.
Revue Cochrane des ECR d'au moins 12 semaines (Jurgens 2012). Les essais menés en dehors du Japon, une fois regroupés, ne montraient pratiquement aucun effet ; les essais japonais étaient trop hétérogènes pour être regroupés et montraient des pertes plus importantes mais incohérentes. Une méta-analyse antérieure (Hursel 2009) a trouvé un effet tout aussi faible, plus important avec une consommation habituelle de caféine plus faible.
The studies · 2
Jurgens 2012, Cochrane Database Syst Rev · Cochrane Database Syst Rev
Hursel 2009, Int J Obes (Lond) · Int J Obes (Lond)
Cognition
Léger regain d'attention à court terme grâce à la théanine associée à la caféine
La théanine et la caféine du thé procurent un léger regain d'attention et de vigilance, de courte durée, plus fiable lorsqu'elles sont prises ensemble comme dans la feuille.
Méta-analyse d'études randomisées (Payne 2025). Les effets étaient aigus et modestes, et la combinaison de L-théanine et de caféine, telle qu'elle se présente dans la feuille, portait le signal le plus net. Voir la page [l-theanine](/go/integrative/practice/l-theanine) pour les preuves complètes.
The study · 1
Payne 2025, Nutr Rev · Nutr Rev
Blood Sugar
Glycémie à jeun et HbA1c: en baisse de 1.6 mg/dL (0.09 mmol/L) et 0.30 % dans une méta-analyse, inchangées dans deux autres
Le thé vert modifie à peine la glycémie. La plus grande revue a trouvé de minuscules baisses de la glycémie à jeun et de l'HbA1c, tandis que deux revues ultérieures chez des personnes à risque de ou vivant avec un diabète de type 2 n'ont trouvé aucun changement.
Liu 2013 pooled green tea beverages and extracts across healthy and at-risk adults and found small but statistically significant reductions in fasting glucose and HbA1c, with a fasting-insulin reduction only in the higher-quality subset. Wang 2014, restricted to people at risk of type 2 diabetes, and Li 2016, restricted to people with established type 2 diabetes, each found no significant change in fasting glucose or HbA1c, so the small pooled signal does not hold in the groups who would most want it.
Who this may not transfer to:Pooled from trials spanning healthy, at-risk and type 2 diabetic adults of both sexes. The small reductions came from the broadest analysis; in the at-risk and diabetic subgroups, where a glucose effect would matter most, the meta-analyzes found none.
The studies · 3
Liu et al., effect of green tea on glucose control and insulin sensitivity, a meta-analysis of randomized controlled trials · Am J Clin Nutr
Wang et al., effects of green tea or green tea extract on insulin sensitivity and glycaemic control in populations at risk of type 2 diabetes · J Hum Nutr Diet
Li et al., effects of tea or tea extract on metabolic profiles in patients with type 2 diabetes, a systematic review and meta-analysis · Diabetes Metab Res Rev
Cancer Risk And Outcome
Aucun signe clair que le thé vert prévient le cancer dans les essais
Malgré sa réputation, les essais ne montrent pas que le thé vert prévient le cancer ; la plupart des résultats encourageants proviennent d'études de population qui ne peuvent pas prouver que le thé en était responsable.
Revue systématique Cochrane (Filippini 2020) d'études observationnelles et interventionnelles ; les résultats variaient selon le site cancéreux et la conception de l'étude, et les preuves interventionnelles étaient rares. La cohorte Ohsaki (Kuriyama 2006) a trouvé une mortalité cardiovasculaire plus faible mais pas une mortalité par cancer plus faible, renforçant l'idée que le signal contre le cancer est faible.
The study · 1
Filippini 2020, Cochrane Database Syst Rev · Cochrane Database Syst Rev
How it works
Dépense énergétique sur 24 heures augmentée de 4 % par les catéchines associées à la caféine
Les catéchines du thé vert associées à la caféine ont augmenté la dépense calorique de l'organisme de quelques pourcents sur une journée, plus que ce que la caféine seule pouvait expliquer.
Étude croisée randomisée en chambre respiratoire chez 10 hommes en bonne santé (Dulloo 1999). L'extrait a également augmenté la noradrénaline urinaire, suggérant une activation sympathique. Il s'agit d'une petite étude mécanistique ; elle démontre la voie thermogénique, pas un changement de poids cliniquement significatif.
Who this may not transfer to:Measured only in 10 healthy men. Thermogenesis and catecholamine response can differ with body composition and sex hormones, so the size of any energy-expenditure effect in women is not established here, only plausible.
The study · 1
Dulloo 1999, Am J Clin Nutr · Am J Clin Nutr
Activité des ondes cérébrales alpha en hausse dans les 45 minutes environ suivant la prise de L-théanine
La L-théanine du thé oriente le cerveau vers un état calme mais éveillé, visible sur un EEG, ce qui explique pourquoi le thé apaise sans sédater.
Études EEG humaines résumées dans Nobre 2008 ; une faible dose a augmenté l'activité alpha, distinguant le calme du thé de la sédation. Il s'agit d'un marqueur mécanistique sous-jacent à l'expérience de calme-vigilance, non d'un résultat clinique.
The study · 1
Nobre 2008, Asia Pac J Clin Nutr · Asia Pac J Clin Nutr
How It Works
The cardiovascular numbers trace to the catechins, EGCG chief among them, acting on blood vessels and metabolism. In the vessel lining, catechins help keep nitric oxide available, the signal that relaxes the artery wall. That is a credible route to the lower pressure. In the gut, catechins reduce how much cholesterol is absorbed, which is the route to the lipid change. Caffeine and catechins together also raise energy expenditure and fat oxidation by a few percent, the mechanism behind the thermogenesis claims.
The calm alertness runs on a separate route. L-theanine reaches the brain within roughly 60 minutes and shifts the balance toward calm, while the caffeine raises arousal. The two effects do not cancel. Together they help focus and memory without the jitter of coffee. On an EEG, the combination shows up as more alpha activity, the marker of a mind relaxed and awake at once.
Anatomy of the Practice
1Within an hour
The calm-alertness effect appears within an hour of a cup. This is the fast, repeatable response, and it is why a cup of green tea steadies most people.
2Over weeks
With daily green tea, total cholesterol and blood pressure settle a little lower over the weeks the cardiovascular trials measured. This is the effect those trials were built to catch.
3Over years
Over years, whether the drink adds up to less disease and a longer life has only been watched in large populations, never tested in a trial. Those are associations, and the leaf’s own contribution is unconfirmed.
How to Drink It
Almost every finding here came from two or three cups a day. Start there.
Ways to Do It
The benefit is in the drink. A concentrated extract is the only option with a safety caution.
This is the food-first option and the amount behind almost all the evidence. Two or three cups spread through the day supply the catechins, L-theanine, and a modest dose of caffeine. That is the intake behind the cholesterol and blood-pressure findings. Steep at slightly below boiling for a minute or two; water that is too hot makes it bitter without adding benefit.
Matcha delivers a stronger dose, so switching some cups to it is a simple way to raise your intake. Treat the extra caffeine seriously if you are sensitive to it or drinking it late.
Green tea is one source of flavan-3-ol catechins among several; [cocoa](/go/integrative/practice/cocoa-flavanols), apples, and berries carry relatives of the same family. A varied diet covers the compound class without leaning on any single source. It is also the diet pattern the population studies described.
A concentrated green tea extract is the one way to take EGCG far above what the drink provides, and the one option with a documented liver risk. The Cautions below give the dose and safety rules.
Go Deeper
- Caffeine: the stimulant half of tea, how long it lasts in you, and whether an afternoon cup is costing you sleep.
- L-theanine: the amino acid that gives tea its calm, and what the calm-alertness pairing does.
- Cholesterol and lipids: where tea's small drop sits among the levers that move cholesterol, and the ones that move it more.
- High blood pressure: the fuller set of things that lower blood pressure, and how a drink-sized effect compares.
- Focus and memory: the goal the theanine-plus-caffeine lift belongs to, and the other levers for attention.
- Cocoa flavanols: another polyphenol whose short-term vascular markers look good and whose long-term trials came in mixed, a useful comparison for reading this kind of evidence.
The Chinese Medicine View
Chinese medicine reasoned about tea for well over a thousand years, long before any trial existed. Green tea, 綠茶 lǜ chá, holds a settled place in Chinese dietary and medical thought.
Tea is classed as cool in nature, bitter and sweet in flavor, entering the Heart, Lung, and Stomach. Its recorded actions read close to what a modern drinker wants from it:
- clears heat, and clears the head and the eyes
- lifts and settles the mind, so thinking is sharp without agitation
- transforms phlegm
- quenches thirst
- promotes urination
- helps resolve food stagnation after a rich meal
The clearing-the-head quality, an unclouded alertness, is the traditional description that sits nearest to the calm-alertness that L-theanine and caffeine produce. That closeness does not make the old account a prediction of the chemistry; the tradition reasoned about a whole leaf, centuries before anyone isolated EGCG.
The tradition is at its most useful in saying plainly that tea does not suit everyone. Its cool, downward-moving nature is wrong for someone who runs cold, and its bitterness can burden a weak digestion. A cold, damp constitution or a delicate stomach is the tradition's signal to go easy: keep the tea weak, and never drink it strong on an empty stomach. Drunk to excess or late, a cooling stimulant is understood to unsettle the Shen, the spirit that should quiet at night. If you work with a practitioner, tea is a reasonable thing to ask about.
Cautions For This Practice
Everything to be aware of is here, in one place. This practice suits most healthy people; a few situations call for real care.
L'extrait concentré a endommagé le foie à des doses de 140 à 1,000 mg d'EGCG par jour
Revue systématique de l'USP (Oketch-Rabah 2020) portant sur des données animales, humaines et des rapports de cas ; elle a conduit l'USP à ajouter une mise en garde sur l'étiquette recommandant de prendre l'extrait avec de la nourriture, non à jeun, et d'arrêter et de consulter en cas de signes de trouble hépatique. La boisson n'était pas mise en cause.Oketch-Rabah 2020, Toxicol Rep
Enzymes hépatiques élevées chez 6.7 % avec 843 mg d'EGCG par jour, contre 0.7 % sous placebo
Analyse de sécurité du Minnesota Green Tea Trial (Dostal 2015). Les événements indésirables globaux étaient pour la plupart légers, mais l'élévation de l'ALT était clairement liée à la dose de l'extrait concentré, ce qui concorde avec la revue de l'USP sur l'hépatotoxicité. L'essai utilisait un extrait, pas du thé infusé.Dostal 2015, Food Chem Toxicol
Liver injury from concentrated extract, not from the drink
A United States Pharmacopeia review of case reports and trials concluded that high-dose green tea extract can cause liver injury. Reported doses ran from about 140 mg to roughly 1,000 mg of EGCG a day, and susceptibility varied widely between people. Taking it on an empty stomach raised the exposure. In the Minnesota Green Tea Trial, 6.7% of women on 843 mg of EGCG daily had raised liver enzymes, against 0.7% on placebo. The brewed drink is not implicated. If you use an extract: take it with food, keep the dose modest, and avoid it if you have any liver problem. Stop and see a clinician for abdominal pain, dark urine, or yellowing of the skin or eyes.
The caffeine, and more of it in matcha
Green tea carries caffeine, and matcha carries more because you drink the whole leaf. That is enough to affect sleep, reflux, anxiety, or heart rhythm in people sensitive to caffeine, and enough to matter if you are already limiting it. The timing and dose rules are on the [caffeine](/go/integrative/practice/caffeine) page. A late or large green tea is a real caffeine dose: count it as one.
Iron absorption at meals
The tannins in tea reduce how much non-heme iron the gut absorbs from plant foods, which matters mainly for people who are iron-deficient, anemic, or relying on plant iron. The simple fix is to drink tea between meals and to keep it away from an iron supplement.
Medications and blood thinners
Green tea contains vitamin K, and its catechins can change how some drugs are handled. If you take warfarin, another anticoagulant, or a narrow-margin drug, keep your intake steady and tell your prescriber. A concentrated extract is more likely to interact than the occasional cup.
Pregnancy, breastfeeding and high-dose use
In pregnancy, the concern is caffeine, and moderate tea is generally within limits. A concentrated extract is not advisable without a clinician’s approval. Discuss any high-dose or supplement use, in pregnancy or alongside other treatment, with your clinician first.
Start slow, be smart, read the research, and consult a professional if you have any concerns. This is here to inform your choice, not make it for you.
Common Questions
Does green tea prevent cancer?
The largest careful review, a Cochrane analysis, found the human data limited and inconsistent, resting mostly on observational studies. Those studies cannot separate the tea from the healthier lives of the people who drink it. In the large Ohsaki cohort in Japan, regular drinkers had less heart-disease death but no reduction in cancer death.
Treating green tea as cancer protection goes past what the trials support.
Is matcha better than regular green tea?
It is stronger, and whether that counts as better depends on what you want. Because you drink the whole leaf, the dose is larger. That helps if you want more from the drink. It is also a reason for more care with caffeine if you are sensitive, prone to reflux, or drinking it in the afternoon.
Does it help you lose weight?
The weight change measured over months is small. In the Cochrane review it was not clinically important, and the pooled result outside Japan came to essentially zero. Green tea is a fine drink in place of sugary ones, and that swap probably does more for weight than the leaf itself.
Does it lower blood sugar?
The largest meta-analysis, 17 trials in 1,133 people, found fasting glucose down 1.6 mg/dL (0.09 mmol/L) and HbA1c down 0.30%. Both are small. Two later reviews found no change at all: one in people at risk of type 2 diabetes, another in people who already have it.
Explore Related
Other pages this one connects to, by the evidence they share, the outcomes they touch, and the ground they cover.
All 15 sources on this page independently checked and cross-referenced.
Thomas Dehli, Founder & Editor, Sacred Lotus
Sacred Lotus has published Chinese medicine reference material since 2001. Integrative pages are held to the same standard as the herb and formula library: cite the source, grade the claim at its real strength, and say where the research has not looked. This page is educational and it is not medical advice. Last reviewed and updated August 9, 2026.
Evidence strength
How confidently the research supports a claim. Strength describes the evidence, not our endorsement.