Green Tea

Green Tea

Green tea (Camellia sinensis) is one of the most studied drinks in the world, with thousands of clinical and epidemiological publications. It originated in Japan and China, where it has been consumed for thousands of years both as a drink and as a medicine.

Green tea, black tea and white tea all come from exactly the same bush. The only thing that sets them apart is what happens to the leaf after picking: for green tea the leaf is steamed or pan-fired immediately, which deactivates the enzyme polyphenol oxidase and stops oxidation. As a result, the catechins — a group of polyphenols that underlies most of its benefits — are preserved almost entirely, instead of being converted into theaflavins as in black tea.

Is there caffeine in green tea?

Yes. A cup of green tea (240 ml) usually contains 20-45 mg of caffeine — a third to a half of the caffeine in a cup of drip coffee (95-165 mg). Matcha has more, about 60-70 mg, because you drink the whole ground leaf and not just the infusion.

The exact amount depends less on the type of tea and more on how it is prepared:

The caffeine in green tea comes with L-theanine, which slows its absorption and softens its effect — so it is experienced as moderate, lasting alertness rather than a sharp spike followed by a crash. That is why many people tolerate green tea even when coffee makes them jittery or anxious.

Decaffeinated green tea keeps most of the catechins but loses the alertness effect. The decaffeination method matters: carbon dioxide (CO₂) decaffeination preserves EGCG much better than decaffeination with the solvent ethyl acetate, which can remove up to about 70% of the catechins.

Green tea extract — what it is and when it’s a problem

Green tea extract (GTE) is the catechins from the leaf concentrated into a powder or capsule. It is not the same as drinking tea, and the difference is not only in strength.

• How many times stronger: a cup of green tea provides about 50-100 mg of EGCG. An extract capsule usually provides 200-400 mg, and sometimes as much as 700 mg — meaning one capsule is equivalent to 4-10 cups.
• The liver problem: the European Food Safety Authority (EFSA) determined that intake of 800 mg of EGCG or more per day from extract is associated with raised liver enzymes. Dozens of cases of acute liver injury (hepatotoxicity) linked to green tea extract supplements have been documented, mainly when taken on an empty stomach — where blood EGCG levels jump 3-5 times higher.
• The tea itself was not found to be a problem. The same EFSA review found no concern with drinking green tea as a beverage, even in large amounts. The difference is the concentration and the rate of absorption.
• What does work: studies that showed a significant metabolic effect mostly used 250-500 mg of EGCG a day, usually combined with caffeine. The effect on weight was consistent but small — about 1-1.5 kg over 12 weeks.

The practical conclusion: if you want the benefits, 3-4 cups of tea a day provide a similar range of EGCG without the liver risk. If you take extract anyway — not on an empty stomach, not above 400 mg of EGCG a day, and not alongside drugs processed by the liver.

More detail: what EGCG is, the effective dose and the side effects.

Which green tea is best?

The practical choice for most people is whole-leaf Japanese sencha. It provides most of the benefit at a reasonable price. Matcha is better for those who want the maximum concentration and are willing to pay, but with matcha it is especially important to choose a quality grade (ceremonial) and a known source — because you drink the whole leaf, any heavy metals and fluoride it absorbed are consumed in full as well.

Whole leaves over tea bags: tea bags usually contain “dust” and low-grade leaf fragments that have lost some of their volatile oils. Whole leaves provide a higher catechin concentration and a cleaner flavor.

Research-based health benefits

• EGCG (epigallocatechin gallate): the main catechin in green tea and one of the most powerful known antioxidants. It inhibits oxidative enzymes, reduces inflammation, and is linked to activity against tumor growth in lab studies. It makes up about 50%-60% of the leaf’s total catechins.

• The caffeine + L-theanine combination: caffeine increases alertness, focus and metabolic rate. L-theanine — an amino acid almost unique to tea — increases alpha brain waves and balances the effect of caffeine. The combination creates a state of “calm alertness” considered a natural nootropic formula.

• Heart health: large prospective studies in Japan (the Ohsaki study, about 40,000 participants) found an association between drinking 3-5 cups a day and lower mortality from heart disease and lower stroke rates. Catechins reduce LDL oxidation and improve endothelial function.

• Fat metabolism: EGCG inhibits the enzyme COMT, which breaks down norepinephrine, and so prolongs the action of the sympathetic nervous system. The effect is real but modest — on the order of 3%-4% of daily energy expenditure, not “fat burning” on a scale that justifies the marketing.

• Insulin sensitivity: regular consumption has been linked to improvements in fasting glucose and in the insulin response to a meal.

• Brain health: EGCG has been studied for neuroprotection against Alzheimer’s and Parkinson’s, possibly by reducing the buildup of beta-amyloid and alpha-synuclein. The evidence is still early and based mainly on models.

• Oral health: catechins inhibit Streptococcus mutans, the main bacterium behind cavities, and the leaf’s natural fluoride also contributes.

Downsides and considerations

• Inhibits iron absorption: tannins and catechins form complexes with non-heme iron from plant sources and reduce its absorption by 25%-50%. This is the most significant downside for people prone to anemia. The solution is simple: drink tea between meals, at least an hour apart, and not with them.

• Caffeine and sleep: if you are sensitive to caffeine, don’t drink it after 2:00 p.m. (14:00). Caffeine’s half-life is 5-6 hours in the average person, and up to 9 hours in slow metabolizers.

• Fluoride: the tea leaf absorbs fluoride from the soil, and it accumulates especially in the older leaves used for cheap tea. Drinking more than 8-10 cups a day for years has been linked to fluoride buildup in the bones. At 2-4 cups the risk is negligible.

• Concentrated extract and the liver: as detailed above — the risk is in supplements, not in the drink.

• Drug interactions: green tea contains vitamin K and may interfere with warfarin, and catechins affect CYP enzymes and the absorption of some drugs (including nadolol and some statins).

• Bitterness from incorrect brewing: boiling water extracts excess tannins and catechins from the leaf and creates intense bitterness. This is the most common reason people “don’t like green tea.”

How to brew it properly

1. Temperature: 70-80°C (158-176°F). Boil and wait 3-5 minutes, or pour a little cold water into the kettle. Matcha — 70-75°C (158-167°F).
2. Time: 2-3 minutes for sencha, 1-2 minutes for gyokuro. Longer steeping mainly adds bitterness.
3. Amount: a teaspoon (2-3 grams) per 200 ml.
4. Re-steeping: whole leaves are good for two and even three infusions. The second infusion is richer in L-theanine and mellower.
5. Lemon improves absorption: vitamin C stabilizes catechins in the gut and significantly increases their bioavailability. A slice of lemon is a real upgrade, not just flavor.
6. Don’t add milk: milk proteins bind some of the catechins and reduce their availability.

Summary

2-4 cups of green tea a day are one of the simplest and best-supported additions to your diet — catechins, a balanced caffeine-theanine effect, and a consistent association with cardiovascular health. The practical rules: whole-leaf sencha or matcha, water at 80 degrees and not boiling, between meals and not with them so as not to block iron, and caution with concentrated extracts — that is where the real risk lies, not in the drink.