by Dr. Leo Galland
High intake of soy foods among men is associated with a decreased risk of prostate cancer according to research studies. In laboratory experiments components of soy called isoflavones have shown the potential to inhibit the growth of prostate cancer cells.
Researchers at Stanford University Medical School administered soy isoflavones for 2 weeks to men who were about to have prostate surgery. They found that isoflavone levels in the prostate were 6 times higher than in the blood of the subjects in the study. The isoflavone daidzen was taken up by the prostate much more avidly than the isoflavone genistein.
Writing in the journal The Prostate, the Stanford researchers concluded: “The findings from the present study suggest that prostate tissue may have the ability to concentrate dietary soy isoflavones to potentially anti-carcinogenic levels.” (Gardner et al.)
References and Abstracts:
Am J Clin Nutr. 2009 Apr;89(4):1155-63. Epub 2009 Feb 11.
Soy consumption and prostate cancer risk in men: a revisit of a meta-analysis.
Yan L, Spitznagel EL.
Grand Forks Human Nutrition Research Center, ARS, USDA, Grand Forks, ND 58202-9034, USA. lin.yan@ars.usda.gov
BACKGROUND: Epidemiologic studies have shown that the consumption of soy foods may be associated with a reduction in cancer risk in humans.
OBJECTIVE: The purpose of this study was to conduct a meta-analysis on the association between soy consumption and prostate cancer risk in men.
DESIGN: We systematically reviewed studies obtained through a thorough Medline literature search and identified 15 epidemiologic publications on soy consumption and 9 on isoflavones in association with prostate cancer risk. We extracted the most adjusted relative risks (RRs) and odds ratios (ORs) of the highest and the lowest reported categories of intake from each study and conducted this analysis using a random-effects model in which studies with smaller SEEs are given greater weight in the summary measure.
RESULTS: Our analysis of studies on soy intake yielded a combined RR/OR of 0.74 (95% CI: 0.63, 0.89; P = 0.01). When separately analyzed, studies on nonfermented soy foods yielded a combined RR/OR of 0.70 (95% CI: 0.56, 0.88; P = 0.01) and those on fermented soy foods yielded a combined RR/OR of 1.02 (95% CI: 0.73, 1.42; P = 0.92). The analysis of studies on isoflavones yielded a combined RR/OR of 0.88 (95% CI: 0.76, 1.02; P = 0.09). Further separate analyses showed a combined RR/OR of 0.52 (95% CI: 0.34, 0.81; P = 0.01) from studies with Asian populations and 0.99 (95% CI: 0.85, 1.16; P = 0.91) from studies with Western populations.
CONCLUSIONS: The results of this analysis suggest that consumption of soy foods is associated with a reduction in prostate cancer risk in men. This protection may be associated with the type and quantity of soy foods consumed.
Prostate. 2009 May 15;69(7):719-26.
Prostatic soy isoflavone concentrations exceed serum levels after dietary supplementation.
Gardner CD, Oelrich B, Liu JP, Feldman D, Franke AA, Brooks JD.Department of Medicine, Stanford Prevention Research Center, Stanford University Medical School, Stanford, California 94305, USA. cgardner@stanford.edu
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.
