Red clover is one of the herbs that commonly stirs up controversy regarding it’s safety with patients that have hormonally driven tumors. Some practitioners routinely avoid isoflavone containing herbs and foods because of the possibility of antagonizing estrogen receptor positive tumor cells. An overview of the data shows that although there are some studies showing a stimulating effect of these isoflavones in vitro, clinical and epidemiological data does not generally support the conclusions of these studies. Also, isolating and concentrating these isoflavones tends to have a very different effect then when they are administered as part of a whole plant or food. The estrogenicity of red clover is estimated to be weak at best, and this study shows that the isoflavone biochanin A markedly inhibits aromatase of estrogen, decreasing the body’s endogenous estrogen production. It could be that avoiding clover or other herbs and foods because of their reputed estrogenicity could be throwing the baby out with the bathwater.
 
The red clover (Trifolium pratense) isoflavone biochanin A inhibits aromatase activity and expression.Wang Y, Man Gho W, Chan FL, Chen S, Leung LK.
Department of Biochemistry, The Chinese University of Hong Kong, Shatin NT, Hong Kong.