A Phase II randomized, placebo-controlled clinical trial of purified isoflavones in modulating steroid hormones in men diagnosed with localized prostate cancer

Nutr Cancer. 2007;59(2):163-8. doi: 10.1080/01635580701432678.


Our purpose was to evaluate the safety and effectiveness of purified isoflavones in producing an increase in plasma isoflavones and a corresponding change in serum sex hormone binding globulin (SHBG) and steroid hormone levels in men diagnosed with early stage prostate cancer. In this Phase II randomized, double-blinded, placebo-controlled trial, 53 prostate cancer patients with a Gleason score of 6 or below were supplemented with 80 mg purified isoflavones or placebo for 12 weeks. Changes in plasma isoflavones, serum steroid hormones, and safety markers were analyzed from baseline to 12 wk. A total of 50 subjects completed the study. Although significant increases in plasma isoflavones (P < 0.001) was observed with no clinical toxicity, the corresponding modulation of serum SHBG, total estradiol, and testosterone in the isoflavone-treated group compared to men receiving placebo was nonsignificant. Increasing plasma isoflavones failed to produce a corresponding modulation of serum steroid hormone levels in men with localized prostate cancer. The study establishes the need to explore other potential mechanisms by which prolonged and consistent purified isoflavone consumption may modulate prostate cancer risk.

Publication types

  • Clinical Trial, Phase II
  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural

MeSH terms

  • Aged
  • Aged, 80 and over
  • Antineoplastic Agents, Phytogenic / adverse effects
  • Antineoplastic Agents, Phytogenic / blood
  • Antineoplastic Agents, Phytogenic / therapeutic use*
  • Dietary Supplements
  • Double-Blind Method
  • Estradiol / blood
  • Humans
  • Isoflavones / adverse effects
  • Isoflavones / blood*
  • Isoflavones / therapeutic use*
  • Male
  • Middle Aged
  • Neoplasm Staging
  • Phytoestrogens / metabolism
  • Prostatic Neoplasms / drug therapy*
  • Safety
  • Sex Hormone-Binding Globulin / metabolism*
  • Testosterone / blood
  • Treatment Outcome


  • Antineoplastic Agents, Phytogenic
  • Isoflavones
  • Phytoestrogens
  • Sex Hormone-Binding Globulin
  • Testosterone
  • Estradiol