How we rate
“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.
Green tea
Slightly lowers LDL cholesterol, blood sugar and blood pressure; almost nothing on weight, and a real risk to the liver at high doses in capsules.
Benefits
- Lowers total cholesterol and LDL: meta-analysis of 14 trials on 1,136 adults, confirmed by another of 20 trials on 1,415 people (145 to 3,000 mg of catechins per day, 3 to 24 weeks), with no effect on HDL
- Lowers blood pressure by 2.08 mmHg for systolic and 1.71 mmHg for diastolic (meta-analysis of 13 trials), slightly more when baseline systolic reaches 130 mmHg
- Lowers fasting blood sugar and HbA1c (meta-analysis of 17 trials, 1,133 people)
- With exercise, about 625 mg of catechins per day for 12 weeks caused greater loss of abdominal fat and lower triglycerides compared to exercise without catechins in overweight adults
- A dose of 366 mg of EGCG increased fat utilization by 17% during exercise in healthy young men
- In 128 women over 75 years old with sarcopenia, exercise combined with catechins improved walking and leg muscle mass, compared to simple health education
Precautions
The liver first. EFSA notes rare cases of liver damage with supplements, and rising transaminases in trials starting from 800 mg of EGCG per day. In the largest trial, 843 mg of EGCG per day for one year in 1,075 postmenopausal women, 6.7% had elevated ALT (a liver enzyme), including 1.3% severely, along with more nausea and skin reactions. Out of 1,414 patients with supplement- or medication-related liver injuries, 40 cases were attributed to green tea, often severe, sometimes leading to transplantation, and linked to a gene (HLA-B*35:01) suggesting an individual-specific reaction. The US Pharmacopeia review recorded 216 reports, including 34 liver damages, more frequent with a concentrated extract taken on an empty stomach; one case of acute liver failure has also been published. The trial finding weight loss used 856.8 mg of EGCG per day, above EFSA's 800 mg threshold. Limitations: on weight, the Cochrane review finds a small, clinically insignificant loss and no effect on weight maintenance; another meta-analysis mentions a small effect. The effect on fat utilization at rest and during exercise is deemed inconclusive by one review. The effects on blood sugar partly come from at-risk individuals, such as the trial in 60 volunteers with borderline diabetes.
Recommended dosage
456 to 625 mg of catechins per day in two trials; in capsules, no more than 338 mg of EGCG per day (level deemed safe)
How to take it
- Dose: a systematic review considers 338 mg of EGCG per day in capsules or tablets and 704 mg in beverage to be safe; EFSA sees liver transaminases rise starting from 800 mg of EGCG per day as a supplement.
- Not on an empty stomach: the US Pharmacopeia review finds more side effects when the concentrated extract is taken on an empty stomach.
- No high doses all at once: liver injuries appear mostly with concentrated preparations taken at high doses all at once.
- Infusion or extract: according to EFSA, catechins from traditional infusions are generally safe at usual doses; the risk to the liver is described with concentrated supplements.
- With exercise: about 625 mg of catechins per day, in a beverage, for 12 weeks in the trial on abdominal fat.
- What doesn't work: 300 mg of EGCG per day for 12 weeks made no difference to fat loss in 83 dieting women.
Did you know?
In 10 men, a green tea extract increased 24-hour energy expenditure by 4%, more than caffeine alone.
What the studies say
This meta-analysis of 13 randomized controlled trials evaluated the effect of green tea consumption on blood pressure and other parameters. It showed a significant reduction in systolic blood pressure (-2.08 mmHg) and diastolic blood pressure (-1.71 mmHg). In addition, significant decreases in total cholesterol and LDL cholesterol were observed. The effects on blood pressure appeared more pronounced in participants with systolic pressure greater than or equal to 130 mmHg and when consuming green tea extracts.
Khalesi S, Sun J, Buys N, Jamshidi A, Nikbakht-Nasrabadi E, Khosravi-Boroujeni H. — European journal of nutrition (2014) — View the source study
For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more