Is Green Tea Good for You? What the Evidence Actually Says

Search for green tea in English and you will find it described as an antioxidant powerhouse, a metabolism booster, and a cancer preventative. Search for it in Japanese and you will mostly find people arguing about which bottled brand tastes best.

Both of those are describing the same leaf. The difference is that one market sells it as a supplement and the other sells it as a drink.

That distinction turns out to be the single most useful thing to hold on to, because the evidence for green tea as a beverage and the evidence for concentrated green tea extract point in different directions — and almost every confusing headline comes from mixing them up.

This article is not medical advice. It is a summary of what published research does and does not establish. If you have a condition, are pregnant or nursing, or take medication, ask a doctor rather than a tea blog.

What the large studies actually found

The best-known of the cohort studies followed 40,530 Japanese adults aged 40 to 79 from 1994, and reported that higher green tea consumption was associated with lower mortality, particularly from cardiovascular causes.

Kuriyama S. et al., "Green tea consumption and mortality due to cardiovascular disease, cancer, and all causes in Japan: the Ohsaki study", JAMA 2006;296(10):1255–65.

That is a real result from a large, careful study. It is also where the trouble starts.

Why "associated with" is doing a lot of work

A cohort study observes people and records what happens to them. It cannot tell you that the tea caused the outcome — only that tea-drinking and the outcome travelled together.

And in Japan, tea-drinking travels with a great deal else. People who drank five cups a day in 1994 were, on average, doing plenty of other things at once: eating a Japanese diet heavy in fish and vegetables, smoking at different rates than the low-tea group, sitting down to meals at home rather than eating on the move. Researchers adjust for the factors they measured. They cannot adjust for what they did not.

This is not a reason to dismiss the findings. It is a reason to read them as what they are: a plausible signal, from a population whose entire way of eating differs from the reader's, that has not been confirmed by the kind of trial that could establish cause.

The trials that can establish cause — randomised, controlled, giving one group tea compounds and the other a placebo — are mostly short, mostly small, and mostly conducted with extracts rather than brewed tea. Which brings us to the part of this subject where the evidence is genuinely clear, and where it points the other way.

The one thing that is clearly documented

In 2018 the European Food Safety Authority reviewed the safety of green tea catechins and reached a split conclusion that is worth quoting the shape of.

For green tea as a drink — brewed with hot water, plus instant and ready-to-drink products of similar strength — EFSA found no indication of liver harm even at high consumption. The rare human cases reported appeared to be unpredictable individual reactions.

For green tea extract taken as a supplement, EFSA found evidence from clinical trials that doses at or above 800 mg of EGCG per day produced a statistically significant rise in liver enzymes compared with controls. The panel could not identify a dose it was willing to call safe. The EU subsequently required that a daily portion stay under 800 mg of EGCG and that labels carry warnings for under-18s, pregnancy and breastfeeding.

The gap between those two findings is the practical takeaway of this entire article. The compound that the health marketing is built around is the same compound behind the only well-documented risk, and it becomes a risk at concentrations you cannot reach by drinking tea. A capsule is not a strong cup of tea. It is a different product with a different safety profile.

If you want the benefits that the cohort studies gesture at, the version that was actually studied in those populations is the drink.

What nobody in Japan is thinking about

Here is the part that reframes the research.

In a Japanese supermarket, green tea is not in a health aisle. It is in the drinks fridge, next to the coffee and the sports drinks, and people choose between brands the way they choose between colas — by taste and habit. Ask someone why they buy a particular bottled tea and the answer is that they like it, not that it is good for them.

I can say that much from my own week: the tea I drink is bottled, bought at a convenience store, chosen because it tastes better than the alternatives. Health has never been the reason.

This matters for reading the studies. The 40,530 people in that Ohsaki cohort were not a wellness population making a deliberate health choice. They were drinking tea because tea is what you drink — with breakfast, at work, after dinner, without deciding anything. The thing being measured was not a supplement regime. It was ordinary life in a place where tea replaces most other beverages.

Which suggests the useful question is not "should I add green tea to my routine for the antioxidants." It is: what is the tea replacing? A population that drinks unsweetened tea all day is a population not drinking something else all day. That may be doing more work in the data than any catechin.

What this means for your cup

• Drinking green tea appears to be, at worst, harmless, and quite possibly mildly good. That is a modest claim, and it is the honest one
• The benefit most likely to be real is substitution. Unsweetened tea instead of sweetened drinks is a change with well-established effects, and it needs no antioxidant story
• Treat extracts and capsules as a separate decision with a separate risk profile, and read the label
• Caffeine still counts. Matcha and gyokuro carry a lot of it, which matters more day to day than any of the above. We covered where each tea sits
• Do not drink tea instead of getting a symptom looked at. No cup does that job

If substitution is the part worth acting on, the practical problem is volume: you need unsweetened tea available in the quantity you would otherwise drink something else. Cold brewing a jug overnight solves that more reliably than brewing cup by cup, and it makes no claim beyond being an easy way to have tea in the fridge:

The short version

• Large Japanese cohort studies link tea drinking with lower mortality; they cannot show that tea caused it
• Those populations differ from most readers' in almost every other respect too
• Controlled trials are short, small, and mostly test extracts rather than tea
• EFSA (2018): no indication of liver harm from the drink; documented enzyme elevation from supplements at 800 mg EGCG per day or more
• The most defensible reason to drink it is that it is a pleasant drink with no sugar in it
• In Japan, nobody is drinking it for their health, and the research population was not either

This article is not medical advice. If you are pregnant, nursing, taking medication, or managing a liver condition, speak to a doctor — particularly before taking any concentrated green tea supplement.

For the practical number that actually affects your day, see how much caffeine is in each Japanese tea. And for what tea drinking in Japan really looks like, read what Japanese people actually drink.