But the dietary supplement didn't have the same effect in men who had undergone surgery, radiation or hormone therapy for prostate cancer, say researchers from the University of California, Davis Cancer Center.
PSA is a blood marker for prostate cancer. An increase is PSA is a warning sign of first-time prostate cancer or a sign of recurrence or progression of the disease in men who have been treated for prostate cancer.
The study included 62 men with prostate cancer and elevated PSA levels. They were given 5 grams a day of genistein concentrated polysaccharide for six months. Sixteen of the men were on watchful waiting for the disease and 46 had undergone surgery, radiation or hormone therapy.
Watchful waiting is recommended for some men with prostate cancer whose cancer causes no symptoms, is expected to grow slowly, and is small and contained within one area of the prostate.
Among the 16 men on watchful waiting, three had to drop out of the study due to diarrhea. Of the 13 who completed the study, eight had a drop in their PSA levels. Those reductions ranged from 3 percent to 61 percent.
The other five in that group had increased PSA levels by the end of the study.
In the group of 46 men who had received treatment, one man had no change in his PSA level and all the rest had increases in PSA.
The study was presented April 30 at the American Urological Association meeting in Chicago.
Here's where you can learn more about prostate cancer.