Prostatic soy isoflavone concentrations exceed serum levels after dietary supplementation.

BACKGROUND

The effects of soy isoflavones on prostate cancer may be concentration-dependent. The impact of soy supplementation on isoflavone concentrations in prostate tissues and serum remain unclear.

OBJECTIVE

To assess and compare concentrations of soy isoflavones in prostate tissue and serum among 19 men with prostate cancer who had elected to undergo radical prostatectomy.

METHODS

Participants were randomized to receive either daily soy supplements (82 mg/day aglycone equivalents) or placebos for 2 weeks (14 days) prior to surgery. Serum samples were obtained at the time of the surgery. Isoflavone concentrations were measured by HPLC/ESI-MS-MS.

RESULTS

The median (25th, 75th percentile) total isoflavone concentration in the isoflavone-supplemented group was 2.3 micromol/L (1.2, 6.9) in the prostate tissue and 0.7 micromol/L (0.2, 1.2) in the serum. Total isoflavone concentrations in this group were an average of approximately 6-fold higher in prostate tissue compared to serum; the tissue versus serum ratio was significantly lower for genistein than daidzein, 4-fold versus 10-fold, P = 0.003. Tissue and serum levels of isoflavones among the placebo group were negligible with a few exceptions.

CONCLUSIONS

The findings from the present study suggest that prostate tissue may have the ability to concentrate dietary soy isoflavones to potentially anti-carcinogenic levels.