Green tea extract (EGCG)

What it is

Green tea is made from the leaves of Camellia sinensis, without fermentation. This preserves the polyphenols, above all the catechins. The most abundant and best studied of these is epigallocatechin gallate, EGCG for short.

Two forms are on the market. Green tea extracts are concentrated extracts from the leaves, often decaffeinated, with catechin content that varies by manufacturer and process. In addition, there is highly purified EGCG with a purity of at least 90 percent. With green tea as a beverage, people in the EU take in 90 to 300 mg of EGCG per day on average; according to EFSA, food supplements provide between 5 and 1,000 mg.

How it is supposed to work

In the lab, EGCG is a jack of all trades. It acts as an antioxidant and, in cell cultures and animal experiments, influences numerous signaling pathways related to inflammation, cell growth and metabolism. That is where the hopes for cancer prevention and healthy aging come from.

In humans, the main effect measured is on energy expenditure. In a study with 10 men in a metabolic chamber, an extract with EGCG and caffeine increased 24-hour energy expenditure by 4 percent and shifted metabolism toward fat burning; caffeine alone did not. The researchers explain this by an activation of the sympathetic nervous system; urinary excretion of noradrenaline rose.

How much EGCG reaches the blood depends strongly on how it is taken. On an empty stomach and as a large single dose, blood levels rise considerably more than with food and spread over the day. That is interesting for the effect and decisive for safety.

What users are looking for

Many reach for green tea extract to help with weight loss, often in fat-burner combinations with caffeine. Others take it as an antioxidant for the heart and blood vessels or in a longevity stack, inspired by the long-lived green tea drinkers in Japan. Many report more alertness and somewhat less appetite. These are user reports that are probably partly due to the caffeine it contains and that, for weight, go beyond what the large analyses show. Green tea extract is often combined with caffeine or L-theanine.

What the studies show

The Minnesota Green Tea Trial

1,075 postmenopausal women took green tea extract with 843 mg of EGCG or placebo daily for one year. Breast density, as a marker of breast cancer risk, did not change overall; only in women aged 50 to 55 was there a signal. Side effects were not more frequent overall than under placebo, but the liver value ALT rose in 6.7 percent, compared with 0.7 percent under placebo. This study is one of the most important foundations of today’s EU upper limit.

The Cochrane review on weight loss

The Cochrane authors analyzed studies of at least 12 weeks in overweight adults. In the studies outside Japan, the weight difference was 0.04 kg, not statistically significant. The Japanese studies ranged from 0.2 to 3.5 kg but were too heterogeneous to pool. An older meta-analysis found a weight loss of 1.31 kg, with larger effects in people used to little caffeine.

The 2018 EFSA opinion

The European Food Safety Authority reviewed all available data on green tea catechins. Its result: tea in usual amounts is considered safe. From 800 mg of EGCG per day from food supplements, liver values rose significantly in studies. A dose that is safe for extracts could not be determined, among other reasons because a single product had been linked to liver damage at as little as 375 mg of EGCG per day.

Where the data stop

For weight loss the data are weak. The Cochrane review sees no clinically relevant effect outside Japan, and where effects do appear, they depend heavily on caffeine. The large analyses do not show a fat-burner effect beyond that of a coffee. Cholesterol and blood pressure are surrogate markers; there are no studies with hard endpoints such as heart attacks for extracts.

For cancer prevention and longevity, hopes remain hopes. The large Minnesota study missed its primary endpoint. In the Interventions Testing Program of the US aging research institute, which tests substances in genetically heterogeneous mice, green tea extract did not significantly extend lifespan. The Japanese cohort data concern tea as part of a lifestyle and showed no association with cancer mortality. Many of the mechanisms of EGCG come from cell cultures with concentrations that are not reached in the blood. Finally, it remains open who has an increased liver risk with extracts: sensitivity varies greatly between individuals, and in case reports damage occurred at as little as 140 mg of EGCG per day.

Status, approval and legal

Green tea extract is permitted in Germany as a food supplement, but has been restricted since EU Regulation 2022/2340. A daily portion must contain less than 800 mg of EGCG, the EGCG content per portion must be stated on the label, plus three warnings: do not take if other green tea products are consumed on the same day; not for pregnant or breastfeeding women or children under 18; not on an empty stomach. Older products could be sold until June 21, 2023. In addition, the extracts are under Union scrutiny: the Commission is to decide within four years whether they will be permanently restricted or banned; I have not yet found a decision. Highly purified EGCG is authorized as a novel food and exempt from this rule. None of the five health claims applied for was authorized. As a medicine, green tea extract exists only as an ointment for genital warts. EGCG is not on the 2026 WADA list.

Safety

The central side effect concerns the liver. The US database LiverTox classifies green tea extract as a well-documented cause of liver damage, with more than 100 described cases, mostly 1 to 6 months after starting. Most recover after stopping, but there are also fatal courses. Therefore: not on an empty stomach and not as a large single dose, not with liver disease, not during pregnancy and breastfeeding. In case of abdominal pain, dark urine or yellowing of the skin, stop immediately and see a doctor. Other side effects are nausea and stomach complaints. Green tea can greatly reduce the absorption of some medicines; with the beta blocker nadolol, blood levels fell by 85 percent. Anyone taking medicines should clarify this beforehand.

Sources

• EFSA ANS Panel, EFSA J 2018 – Scientific opinion on the safety of green tea catechins
• Regulation (EU) 2022/2340 – green tea extracts containing EGCG
• Dostal et al., Food Chem Toxicol 2015 – safety in the Minnesota Green Tea Trial
• Samavat et al., Cancer Prev Res 2017 – green tea extract and breast density
• Jurgens et al., Cochrane Database Syst Rev 2012 – green tea for weight loss
• Xu et al., Nutr J 2020 – meta-analysis of green tea and blood lipids
• Khalesi et al., Eur J Nutr 2014 – green tea catechins and blood pressure
• Strong et al., J Gerontol A 2013 – green tea extract in the Interventions Testing Program
• LiverTox (NIH) – Green Tea
• Misaka et al., Clin Pharmacol Ther 2014 – green tea and nadolol