Green tea's ability to fight cancer is even more potent and varied than scientists suspected, say researchers who have discovered that chemicals in green tea shut down one of the key molecules targeted by tobacco to cause cancer.
This could help explain why people who drink green tea are less likely to develop cancer, say the scientists at the University of Rochester's Environmental Health Science Center.
Green tea has been linked for some time to strong anti-cancer effects as well as other purported abilities such as preventing rheumatoid arthritis and lowering cholesterol, but scientists still do not know how the substance works. It is thought that the tea's antioxidants could fight harmful molecules but the Rochester team, writing in the July 21 issue of Chemical Research in Toxicology, decided to look at its role on the aryl hydrocarbon (AH) receptor.
Director of Rochester's Environmental Health Science Center Dr Thomas Gasiewicz has previously shown how both tobacco smoke and dioxin manipulate the molecule, which frequently helps turn on genes that can be harmful, causing havoc within the body.
"It's likely that the compounds in green tea act through many different pathways," said Gasiewicz. "Green tea may work differently than we thought to exert its anti-cancer activity."
The team isolated the chemicals that make up green tea and found two that inhibit AH activity - epigallocatechingallate (EGCG) and epigallocatechin (EGC), both similar to other flavonoids found in broccoli, cabbage, grapes and red wine that are known to help prevent cancer.
These chemicals shut down the AH receptor in cancerous mouse cells, and early results indicate the same is true in human cells as well, reported the researchers.
THe AH-inhibiting effects of green tea become evident when EGCG and EGC reach levels typical of those found in a cup of green tea, said the scientists although laboratory tests do not yet guarantee the same effects among the general population. How green tea is metabolized by the body is crucial to its effectiveness, noted the researchers.
"Right now we don't know if drinking the amount of green tea that a person normally drinks would make a difference, but the work is giving us insight into how the proteins work," said graduate student Christine Palermo. "There are a lot of differences between various kinds of green tea, so a lot more research is needed."
It is clear however that green tea is the source of potentially numerous health benefits and as the most popular beverage in the world, it is possibly one of the most acceptable nutraceuticals. Roche recently started commercial production of the tea's active chemical epigallocatechingallate (EGCG), showing the industry's growing interest in its properties.