A mix of dietary supplements including antioxidants and plant-based estrogens may slow the rise of a biomarker for prostate cancer progression in some men, preliminary research suggests.

The study of 37 men with the disease found that 6 weeks on the supplements generally lowered patients’ levels of male sex hormones, which fuel prostate cancer growth, and, in some patients, put the brakes on rising levels of prostate-specific antigen (PSA).

PSA is a protein produced by the prostate gland; rising PSA levels in a man’s blood can signal cancer or, in men already diagnosed with the disease, cancer progression.

However, the PSA effects seen in this study do not necessarily mean the supplement was hindering the men’s tumors from growing, according to the study authors. The question of whether the change in patients’ PSA rise translates into a change in tumor size “remains unresolved,” they report in the International Journal of Cancer.

But more “thought-provoking” is the possibility that diet changes could help lower a man’s risk of developing prostate cancer, said lead study author Dr. Ries Kranse, of Erasmus Medical Center Rotterdam in the Netherlands.

The supplement mixture he and his colleagues studied included a powder-based drink that contained green tea extract, a soy extract supplying estrogen-like compounds called phytoestrogens, and antioxidants such as lycopene. Patients also used margarine spiked with cholesterol-fighting plant sterols and the antioxidants vitamin E and selenium.

The men in the study, all of whom had prostate cancer and rising PSA levels, used the supplements for 6 weeks; each also used inactive, or placebo, supplements for another 6 weeks.

Kranse and his colleagues found that the patients’ male hormone levels were lower when they were on the supplement compared with when they were taking the placebo.

In the 21 men who showed a dip in a hormone measure called the free androgen index, the supplement also appeared to slow rising PSA levels. When these men were on the placebo, it took an average of 36 weeks for their PSA levels to double, versus 115 weeks with the supplement.

This finding, according to Kranse, suggests that if the supplement proves capable of slowing or stopping tumor growth, it would be through the hormonal effects of the estrogen-like compounds.

If this is the case, he said, a “dietary intervention” could eventually serve as an alternative to certain hormone-suppressing drugs used in prostate cancer treatment.

“Much more thought-provoking, however, is the possible role of a change in diet in primary prevention,” Kranse added.

The current findings, he noted, are in line with studies of the general population that suggest diets rich in antioxidants and phytoestrogens may lower the risk of prostate cancer. Fruits and vegetables are prime antioxidant sources, while phytoestrogens are found in foods such as soybeans and soy products, whole grains and flaxseed.

SOURCE: International Journal of Cancer, February 20, 2005.