Green tea long has been touted for its health properties in regards to fending off cancer, heart disease and immune-related diseases, but some researchers think those who take green tea mega-doses should be cautious.

Investigators at the University of Mississippi completed a study on the effect of high doses of the active ingredients in green tea extract (ECG) on hypoxia-inducible factor-1 (HIF-1), a key regulator of how tumor cells adapt to low-oxygen conditions. The trial showed that, at high doses, ECG activates HIF-1, something it does not do in low concentrations; this suggests ECG may suppress new tumors in low doses, but facilitate more aggressive tumors in larger doses. The study was published in a recent issue of the Journal of Natural Products.

The researchers caution the results are preliminary, as the research was done in a lab. They also said the benefits of green tea are evidenced in those who drink the tea, not necessarily those who ingest the substance in a supplement form.

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