Many signs have pointed to green tea's beneficial impact for health, including multiple studies with animals and hints that green tea drinkers and people living in green tea growing areas are less likely to develop cancer.

In this new study, Palermo and his colleagues probe deeply into one of the mechanisms suggested by previous research for how green tea might have beneficial effects. This suggestion is that plant compounds in green tea interfere with a specific molecular action of dioxin, preventing it from turning on genes that are involved in causing cancer.

Reported in this publication in Chemical Research in Toxicology, their results confirm this earlier work and identify the specific plant compounds most likely to be responsible for green tea's action at suppressing gene activation.

The scientists remain uncertain about whether their findings reveal the way green tea has beneficial health effects, however. Their results indicate that the concentrations of the active compounds required to work against dioxin via this mechanism are high compared to the levels reached in people's blood after drinking green tea.

A number of chemical contaminants cause their damaging effects through the molecular pathway that green tea shuts down, including dioxins, some PCBs, and some polycyclic aromatic hydrocarbons among others, contaminants that are virtually ubiquitous. Hence this line of research offers some promising possibilities for preventing diseases. Given how much remains to be learned and confirmed about this, however, long-term prospects for developing chemical treatments to prevent diseases shouldn't diminish efforts to reduce and eliminate exposures in the first place.

They then used some tools out of analytical chemistry to separate the crude extract into different components, as the crude is a complex mixture of multiple plant compounds. That separation then allowed them to confirm the identity of the components.

For the next round of experiments, they bought commercial versions of the identified components and performed a series of experiments with these pure substances, and mixtures thereof. The experiments again looked at whether or not different concentrations of the compounds interfered with dioxin-mediated gene activation.

What does it mean? Most of these results provide support for the idea that people drinking green tea may benefit from the plant compounds' inteference with gene activation via the Ah receptor. That pathway is one of the main molecular mechanisms for toxic effects of dioxin and related compounds.

The principal argument against this conclusion is that the concentrations of the compounds necessary to cause a reduction in gene activation are much higher than what can be measured in people's blood after drinking green tea. Note in the graphs above that the percentage of gene activation does not begin to fall until concentrations are between 10 and 100 µg/ml. Direct measurements in people's blood, in contrast, typically are less than one-tenth this amount.

In evaluating that argument, Palermo et al. pointed to two considerations

In sum, this study adds to a growing body of evidence indicating that drinking green tea brings significant health benefits. It suggests that additional work will further refine what we understand about exactly how green tea has that effect, and this deeper knowledge may point to treatments that prevent cancers even in the face of continuing exposures to dioxins and related compounds.