Distribution of soy-derived phytoestrogens in human breast tissue and biological fluids

Soy-derived phytoestrogens may exert several health-beneficial effects. Although plasma and urine levels of these compounds after ingestion have been thoroughly investigated, little is known about their tissue distribution, which is particularly important for tissues with high endogenous estrogen and estrogen receptor concentrations. We aimed to investigate the concentrations of genistein, daidzein, and equol in human breast tissue homogenate and to compare these with the corresponding values in serum and urine.

A randomized, double-blind, placebo-controlled study was undertaken to evaluate the concentrations of soy-derived phytoestrogens achieved in breast tissue homogenate, serum, and urine after ingestion of either a soy-based food supplement (n = 9) or a placebo tablet (n = 19) for 5 consecutive evenings before aesthetic breast surgery. To account for the heterogeneity of the breast tissue samples, markers for cellularity, epithelial content, blood vessel content, and total fat were determined.

Urine concentrations of genistein, daidzein, and equol were significantly higher in the soy-supplemented subjects than in the subjects ingesting the placebo (P <.05). Only genistein was found to be significantly higher in serum of the soy group than in the placebo group, and no significant differences were found in breast tissue homogenate concentrations of all analytes between the 2 groups.

Intake of soy-based food supplements for 5 consecutive days did not result in significantly higher genistein, daidzein, and equol concentrations in breast tissue homogenate when compared with the placebo group. The concentrations were in the low nanomolar range, whereas in the corresponding serum samples, concentrations were a hundred-fold higher.