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Quick answer
Brewed green tea is a healthy drink for most people. Population studies, especially in Japan and China, link regular green tea drinking with a lower risk of heart disease and stroke, and trials suggest it may slightly lower LDL ("bad") cholesterol. Its gentle caffeine content can improve alertness.
The popular claims for weight loss are mostly overstated: any effect is very small. Green tea extract supplements are not the same as tea. High doses have caused liver injury, and green tea can interact with some medicines.
What is in green tea
Green tea comes from the same plant as black tea, Camellia sinensis, but the leaves are heated soon after picking to stop them oxidising. This keeps high levels of catechins, a group of polyphenols, with the best known being EGCG (epigallocatechin gallate). Green tea also contains:
- Caffeine: about 20 to 45 mg per cup (roughly a third to half of a cup of coffee), depending on the tea and how it is brewed
- L-theanine: an amino acid that may promote calm alertness, especially combined with caffeine
What the research says
Heart and blood vessels
Large observational studies following hundreds of thousands of people have found that regular green tea drinkers have a lower risk of cardiovascular disease and death. A Japanese study of over 40,000 adults found lower cardiovascular death rates in people drinking five or more cups a day. Observational studies cannot prove cause and effect, because green tea drinkers may differ in other healthy ways, but the findings are consistent.
Randomised trials and meta-analyses show green tea or catechins lower LDL cholesterol modestly, on the order of a few percent, and may lower blood pressure slightly.
Weight
Green tea catechins and caffeine may slightly increase energy use. Reviews, including a Cochrane review, found that green tea preparations produced only a very small, not clinically important weight loss in overweight adults, often less than 1 kg, and studies varied a lot.
Alertness and mood
Caffeine improves alertness and reaction time. Small studies suggest the combination of caffeine and L-theanine may improve attention more smoothly than caffeine alone.
Cancer and other claims
Lab studies are interesting, but human studies have not shown that green tea prevents cancer. The evidence is inconsistent, and it should never be used as a cancer treatment.
How to enjoy green tea
- Brew it well: use water just below boiling (about 70 to 80 °C) and steep for 2 to 3 minutes. Boiling water and long steeping make it bitter.
- Two to three cups a day is a sensible amount for most adults and gives a moderate amount of caffeine. Healthy adults can usually have up to about 400 mg of caffeine a day from all sources.
- Avoid late-afternoon cups if caffeine affects your sleep.
- Drink it between meals if you are prone to low iron, because tea reduces the absorption of iron from plant foods.
- Matcha is powdered whole tea leaf, so it contains more catechins and caffeine per serving.
Possible side effects and interactions
Brewed tea side effects are mostly from caffeine: trouble sleeping, jitteriness, a fast heartbeat, headaches, or acid reflux in some people.
Extracts have been linked to rare but serious liver injury, sometimes needing transplantation. Risk seems higher with high doses and fasting.
Interactions:
- Nadolol (a beta-blocker): green tea can greatly reduce its absorption
- Warfarin: large amounts of green tea may contain enough vitamin K to affect warfarin; keep your intake consistent
- Stimulant medicines and other caffeine sources add up
- Iron: reduces absorption of non-haem iron from food
- Some antidepressants and medicines processed by the liver may be affected by high-dose extracts
Who should limit it
- Pregnant women: limit total caffeine to 200 mg a day (about four cups of green tea, counting all other caffeine sources too) and avoid extracts
- People with iron-deficiency anaemia: drink between meals rather than with them
- People with anxiety, palpitations or insomnia that caffeine worsens
- People with liver disease: avoid extracts entirely
- Anyone taking nadolol or warfarin: talk to your doctor or pharmacist
- Children: limit caffeine and avoid extracts
When to see a doctor
- You notice signs of liver problems after taking a supplement: yellow skin or eyes, dark urine, pale stools, abdominal pain or unusual tiredness. Stop the supplement and see a doctor promptly.
- You have palpitations, chest pain or feel faint
- You are managing high cholesterol, high blood pressure or heart disease. Tea can be part of a healthy diet, but it does not replace treatment.
Frequently asked questions
Does green tea help you lose weight?
Only very slightly, if at all. It can be a healthy, unsweetened replacement for sugary drinks, which is where most of its weight benefit is likely to come from.
Is decaffeinated green tea still healthy?
Decaf green tea still contains catechins, although some are lost during processing. It is a good choice if caffeine bothers you.
Does green tea stain teeth?
Less than black tea or coffee, but it can contribute to staining. Rinsing with water afterwards helps. Unsweetened tea is far kinder to teeth than sugary drinks.
How many cups is too many?
For most adults, the limit is set by caffeine: up to about eight cups spread over the day is usually within safe caffeine limits, but most people feel best with fewer.
References
- National Center for Complementary and Integrative Health (NCCIH). Green tea. https://www.nccih.nih.gov/health/green-tea
- Kuriyama S, et al. Green tea consumption and mortality due to cardiovascular disease, cancer, and all causes in Japan: the Ohsaki study. JAMA, 2006.
- Jurgens TM, et al. Green tea for weight loss and weight maintenance in overweight or obese adults. Cochrane Database of Systematic Reviews, 2012.
- European Food Safety Authority (EFSA). Scientific opinion on the safety of green tea catechins. EFSA Journal, 2018.