Epigallocatechin

Epigallocatechin, commonly encountered as its gallate ester epigallocatechin gallate (EGCG), is a type of catechin, a flavanol polyphenol, found predominantly in green tea. EGCG is the most abundant catechin in green tea and is a major contributor to its antioxidant activity.

Chemically, EGCG is the ester of epigallocatechin and gallic acid. It contains multiple phenolic rings and hydroxyl groups that confer strong radical-scavenging properties. In black tea, much of the EGCG is oxidized during processing, resulting in lower levels compared to green tea.

Oral EGCG undergoes limited absorption in the small intestine, and systemic availability is further reduced by rapid metabolism and conjugation in the intestinal wall and liver (glucuronidation, sulfation, and methylation). The gut microbiota also contribute to its biotransformation, producing various metabolites.

Biological effects attributed to EGCG include antioxidant, anti-inflammatory, and potential anti-carcinogenic activities in experimental systems. It can modulate cell signaling pathways such as MAPK and NF-kB and influence energy metabolism. Evidence from human studies is mixed, and EGCG is not approved as a medical treatment or disease cure.

Safety considerations surround high-dose EGCG supplementation, which in some instances has been linked to liver injury. Typical amounts obtained from normal dietary green tea consumption are considered safe for most people, though individual tolerance varies. Cautions include avoiding very high doses, especially on an empty stomach or in individuals with liver disease or who consume alcohol regularly.