Detection of estrogenic activity in herbal teas by in vitro reporter assays

Herbal teas have become popular as alternatives to caffeinated beverages during past two decades. However, toxicological studies of herbal teas have been limited and the safety of herbal teas thus remains unknown. We focused on the estrogenic activities of herbal teas since some of their ingredients are similar to those used in herbal remedies for menopause relief and therefore contain phytoestrogens. To investigate the potential estrogenic activity of extracts prepared from herbal tea mixtures commercially available and to provide useful information for the safety assessment of those products, we initially screened the estrogenic activity in extracts of 15 different herbal teas by an assay using recombinant yeast cells expressing the human estrogen receptor (YES). A distinct estrogenic activity was thus detected in the ethanolic extracts from four herbal tea mixtures. Licorice root was specified as a ingredient responsible for the estrogenic activity in those extracts. In contrast, the aqueous extracts of all herbal tea mixtures we tested exhibited distinct estrogenic activity in YES, thus suggesting the existence of various ingredients that contain estrogenic constituents extractable with water. Among them, the extract of peppermint tea exhibited the highest estrogenic activity. The estrogenic activity in extracts of herbal tea mixtures and specified ingredients were thereafter confirmed by a reporter assay system using transiently transfected HEK293 cells.