The explanation is long and a little contorted, but it breaks down to this:
Green tea contains a flavonoid called epigallocatechingallate (EGCG). EGCG binds to HSP90, a "chaperone" protein that binds to many different cells and receptors in the body. HSP90 is found in elevated levels in many cancer cells. When bound to EGCG, HSP90 is no longer capable of activating the aryl hydrocarbon (AH) receptor. The AH receptor, in turn, has been shown to turn on often harmful genes in the human body when exposed to dioxin and chemicals found in cigarette smoke. These genes, when activated, are what can turn normal cells into cancer cells.
This concludes today's lecture on biochemistry. :) But seriously, folks, this is a good example of how complex the chemical reactions in the body are.
The article also comments that such results will someday allow the production of pharmaceuticals that contain these health-promoting compounds. Yes, but many folks believe that it's better to get health-promoting nutrients directly from their natural source!
For instance, taking a green tea pill or other extract also introduces the danger of "too much of a good thing." After all, aspirin was touted as a miraculous pain reliever, but taking too much of it can have life-threatening results.
Besides, science is far from knowing how the natural compounds in green tea act together to promote good health. Besides, you have to wonder what sort of chemicals are used in making today's green tea extracts. Finally, who knows what other disease-fighting compounds there are in green tea yet to be discovered? It's better to be safe and get them all by drinking real, honest-to-goodness green tea!