Green tea contains epigallocatechin gallate, or EGCG, the most abundant flavonoid in tea, alongside other catechins, theanine, and caffeine. The combination of these compounds produces effects that differ from those of coffee or isolated caffeine supplementation. The strongest evidence comes from large Japanese population studies where green tea is consumed habitually, and from laboratory and clinical trials examining specific mechanisms.
The Evidence by Condition
- Cardiovascular: a prospective study of 40,000 Japanese adults found that those drinking 5 or more cups of green tea daily had a 26 percent lower risk of cardiovascular mortality than those drinking less than 1 cup; effect sizes were larger in women
- Cognitive decline: a cross-sectional study of 1,000 Japanese adults found that green tea consumption was inversely associated with cognitive impairment; EGCG inhibits beta-amyloid aggregation in laboratory studies
- Cancer: the relationship is complex and varies by cancer type; strongest evidence for reduced risk of prostate cancer and certain gastrointestinal cancers in population studies; less clear for other types
- Metabolic: a meta-analysis of 17 RCTs found green tea catechins modestly reduced body weight and fasting glucose, with effects stronger in studies without additional caffeine supplementation
The Appropriate Dose
Three to five cups of green tea daily represents the dose range associated with the protective effects in prospective studies. Matcha provides approximately 10 times more EGCG than standard green tea per gram of leaf. High-dose EGCG supplements have been associated with liver toxicity in rare cases; whole tea is safer than isolated supplements at equivalent EGCG doses.