Soy isoflavones and radiation therapy: a pilot study


Soy isoflavones are known to have antioxidant and anti-inflammatory activities and to sensitize prostate cancer cells to radiation therapy.

Ahmad et al. carried out a small, pilot study to explore whether soy isoflavones could reduce risk of complications of radiation therapy among prostate cancer patients. Patients were randomized to receive 200 mg soy isoflavone (Group 1) or a placebo (Group 2) daily for 6 months. Soy isoflavone therapy was started on the first day of radiation therapy. Radiation therapy was administered on a standard schedule for a total of 73.8 to 77.5 Gy. Patients were asked to complete a quality of life questionnaire at 3 and 6 months after initiation of radiation therapy.

The results of this pilot study are as follows:

  • 42 patients were initially enrolled in the study.
  • 26 patients completed the QoL survey at 3 months and 27 patients at 6 months.
  • Urinary, bowel, and sexual adverse symptoms induced by radiation therapy were decreased in Group 1 compared to Group 2 at 3 and at 6 months.
  • At 3 months, patients in Group 1 had less urinary incontinence, less urgency, and better erectile function compared to patients in Group 2.
  • At 6 months, the symptoms of patients in Group 1 were further improved as compared to the symptoms of patients in Group 2.
    • Dripping/leakage of urine: 7.7 percent in Group 1 vs. 28.4 percent in Group 2.
    • Rectal cramping/diarrhea: 7.7 percent in Group 1 vs. 21.4 percent in Group 2.
    • Pain with bowel movements: 0 percent in Group 1 vs. 14.8 percent in Group 2.
  • At 6 months, patients in Group 1 reported a higher overall erectile function (77 percent) than patients in Group 2 (57.1 percent).

The authors conclude that soy isoflavone therapy may be able to reduce the urinary, intestinal, and sexual adverse effects commonly associated with prostate-specific radiation treatment for prostate cancer.

Clearly this is only a pilot study, and a larger trial would help to establish whether this effect is replicated in a larger set of patients. Such an additional study would be a relatively easy “add-on” to a larger trial exploring some other aspect of the role of radiation therapy in management of localized prostate cancer.

It should be noted that soy isoflavones can and do have estrogen-like side effects. Use of soy isoflavones in association with radiation therapy is something patients should discuss with their doctors and not carry out without medical guidance.

One Response

  1. This is really interesting news. I had heard the statistics on Japanese men in Hawaii who ate tofu at least 5 times per week and had 65% less chance of developing prostate cancer than those who ate tofu only once a week or less … but I had never seen the pilot study you’re presenting here. Of course, it’s a slightly different angle than the Japanese men, but very very interesting and promising. Thank you for this post!

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