Green tea extract

Green tea extract is a concentrated pill or powder of green tea's catechins, chiefly epigallocatechin gallate (EGCG). It has caused rare but serious liver injury, Europe's food-safety regulator could not name a dose it considers safe, and longer trials of it on bones, the brain and the gut missed their main goals.

Don't take green tea extract for health or longevity; drink tea instead. The risk is highest at 800 mg of EGCG a day or more and when pills are taken on an empty stomach, but no dose has been shown to be safe.

What it is

Green tea extract packs the leaf's polyphenols, the catechins, into a capsule. The main one is EGCG, the compound behind most of green tea's health claims. A day of ordinary green tea drinking supplies roughly 90–300 mg of EGCG; supplements range from 5 to 1,000 mg a day.

The liver risk

Concentrated catechin supplements have caused rare cases of liver injury, some severe enough to need a transplant. In a US network that tracks drug-induced liver injury, 40 cases were put down to green tea, 3% of all its cases. A third were severe and three people needed a new liver; no one died.

The European Food Safety Authority (EFSA) reviewed the trials in 2018. Doses of 800 mg or more of EGCG a day raised liver enzymes, a sign of liver injury, in some people, and the panel could not identify any supplemental dose it could call safe.^[1] It found no liver harm below 800 mg a day for up to twelve months, though one product caused liver injury at a dose of about 375 mg. In the trials, liver tests were checked regularly and people with abnormal results were taken off the pills; someone buying them in a shop has no such safety net.

Taking the pills on an empty stomach, as a single dose, significantly raises the amount of EGCG reaching the blood compared with taking them with food in split doses, and in animal studies fasting made the extract more toxic.

The injury appears to be an immune reaction with a strong genetic susceptibility. About 72% of the cases that were genetically tested carried one immune-gene variant, HLA-B*35:01, against about 11% of the general population.^[2]

Brewed tea is a different exposure. EFSA considers traditionally brewed green tea safe at usual intakes, though it notes rare liver reactions to tea itself, most probably idiosyncratic.

What it does for blood pressure and blood sugar

In trials, many using concentrated extracts, green-tea catechins lower systolic pressure by about 2 mmHg, more in people whose pressure is already high and more from extracts than from a brewed cup;^[3] the largest recent analysis puts it nearer 1 mmHg.^[4] That is a small effect.

The striking metabolic effects of EGCG come almost entirely from cells and rats, at doses equal to well over a gram of EGCG in a person. In people, a concentrated extract slowed the digestion of starch from a test meal in a 28-person study.^[5]

The longer trials missed their main goals

Bones. A year of high-dose green tea extract in postmenopausal women left bone density unchanged in the 121 women scanned.^[6]
Brain. Adding EGCG to a lifestyle programme for a year in 129 people at genetic risk of Alzheimer's disease missed its main goal.^[7]
Gut. Green-tea catechins with a prebiotic fibre for twelve weeks, in 96 adults, did not reduce belly fat, its main goal, though insulin resistance, a secondary measure, improved; no change in any gut bacterium survived statistical correction.^[8]

Who should be careful

People on bortezomib, a cancer drug. Concentrated green-tea polyphenols weaken it in laboratory and animal studies; there are no human data.^[9]
People on nadolol, a beta-blocker. Even ordinary brewed green tea cut its blood levels sharply; see Tea.

What to do

Skip it. The benefits are small or untested and the liver risk is real.
If you already take it, know where the risk sits: doses of 800 mg of EGCG a day or more, and pills taken on an empty stomach. No dose has been shown to be safe.
Drink tea instead if you want green tea's catechins. The wider evidence on tea is on Tea.