There is evidence that tea consumption can reduce the risk of cardiovascular disease, apparently by lowering cholesterol levels in the blood. Although the mechanisms involved have not been established, one possibility is that tea may inhibit cholesterol synthesis (formation) in the liver. In a recent NCCAM-funded study, researchers from the University of Kentucky examined extracts from both green tea and black tea, as well as some components of green tea, for their effects on the synthesis of cholesterol in liver cells from rats.
Both green tea and black tea extracts decreased cholesterol synthesis in the rat liver cells, green tea by 55 percent and black tea by 78 percent. Both extracts appeared to cause this decrease by acting on enzymes involved in cholesterol synthesis. Epigallocatechin-3-gallate (EGCG), green tea's main polyphenol and generally thought to be responsible for most of its biological activity, was much less effective than whole green tea extract in decreasing cholesterol synthesis, suggesting that other, minor components of green tea may contribute to this effect.
The study's finding that black tea was more effective than green tea in decreasing cholesterol synthesis in rat liver cells was unexpected, as was the finding that EGCG alone was less effective than whole green tea. Additional research may reveal more about the cholesterol-lowering mechanisms of both kinds of tea, for example: Does black tea act mainly by suppressing cholesterol synthesis in the liver or by limiting absorption of cholesterol in the intestine? What constituents in green and black tea are responsible for reducing cholesterol synthesis?
Singh DK, Banerjee S, Porter TD. Green and black tea extracts inhibit HMG-CoA reductase and activate AMP kinase to decrease cholesterol synthesis in hepatoma cells. Journal of Nutritional Biochemistry.;20(10):816–822.2009