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's 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.
Genistein is one of two compounds in soy that belong to a family of chemicals known as isoflavones. Isoflavones are phytoestrogens, plant-based chemicals that mimic the effects of estrogen in the body.
Estrogens are best known for their effects upon the female reproductive system, where they play a major role in ovulation, implantation, pregnancy maintenance, childbirth and lactation. Estrogen is also essential for sperm production in males.
Genistein concentrated polysaccharide has been widely used as a complementary therapy for various cancers in Japan, Korea and other parts of Asia.
The University Researchers say that watchful waiting is recommended for some men with prostate cancer whose cancer causes no symptoms and is expected to grow slowly. Also it 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.
Given the small sample size the results must be interpreted cautiously, it was noted.
The university's Davis Cancer Center researchers Davis reported their findings at a meeting of the American Urological Association in Chicago in April last. Four years ago too the same Centre had presented similar findings, it may be recalled here.
Meanwhile in another study of prostate cancer patients living in California, it was found that most Asian men with the disease survived longer than their white counterparts. The exception was men from South Asia; their survival was worse than that of white men.
The study involved an analysis of data for 108,076 whites and 8840 Asians who were diagnosed with prostate cancer from 1995 to 2004. The cohort included six of the largest ethnic subgroups of Asians: Chinese, Filipino, Japanese, Korean, South Asian, and Vietnamese. South Asians included men from southern India, Pakistan, Bangladesh, Sri Lanka, Nepal, Bhutan and Sikkim.
The overall 10-year prostate cancer-specific death rate was 11.9 percent, according to the report in the medical journal Cancer. The researchers were surprised by "how much variation there was across the Asian groups, all the way from an 8 percent risk of death over 10 years in Japanese men to a 16 percent risk in South Asian men."
All of the Asian groups had worse risk factor profiles than whites, yet only in South Asian men did the profile correspond with poorer survival, said Dr. Anthony S.Robbins of the California Cancer Registry in Sacramento.
Nonetheless, "The take-home message is that for five out of six Asian groups, 'being Asian' was a favorable prognostic factor for prostate cancer survival," Robbins said.
"Obviously, the main question we are still trying to explain is why these five Asian groups had better survival. What is behind the 'Asian edge' in prostate cancer? Diet? Lower comorbidity? Less overweight/obesity?"