Serum prostate-specific antigen but not testosterone levels decrease in a randomized soy intervention among men

Abstract

Background: Low prostate cancer incidence and high soy intake in Asian countries suggest a possible protective effect of soy foods against prostate cancer. The goal of this pilot study was to evaluate the feasibility of a randomized, crossover soy trial among men and to investigate the effects of daily soy intake on serum prostate-specific antigen (PSA) and testosterone levels. Methods: We randomized 24 men to a high or a low soy diet for 3 months. After a 1-month washout period, the men crossed over to the other treatment. During the high soy diet, the men consumed two daily soy servings; during the low soy diet, they maintained their usual diet. During the entire study each man donated four blood samples and five overnight urine samples. Dietary compliance was assessed by soy calendars, 24-h dietary recalls, and urinary isoflavone excretion measured by highpressure liquid chromatography with photodiode array detection. Blood samples were analyzed for serum testosterone and PSA by radioimmunoassay. When necessary, variables were log transformed. Two sample t-tests compared the two groups before each study period. Mixed models incorporating the repeated measurements were used to evaluate the effect of the soy diet on urinary isoflavone excretion and serum analytes. Results: Twenty-three men aged 58.777.2 years completed the study. The compliance with the study regimen was high according to self-reported soy food intake and urinary isoflavone excretion. No significant between-group and within-group differences were detected. During the high soy diet, dietary isoflavone intake and urinary isoflavone excretion increased significantly as compared to the low soy diet. A 14% decline in serum PSA levels (P ¼ 0.10), but no change in testosterone (P ¼ 0.70), was observed during the high soy diet in contrast to the low soy diet. Conclusion: The high adherence as shown by three measures of compliance in this pilot trial demonstrated the feasibility of an intervention based on soy foods among free-living men.

Perspectives on the Role of Isoflavones in Prostate Cancer

“…In another randomized, double-blind trial involving prostate cancer patients with rising PSA levels after radical prostatectomy or radiotherapy, administration of dietary supplements, which included soy and isoflavones, resulted in delayed PSA progression (81). A randomized trial with data from 23 men (aged 58.7±7.2 years) found a 14% decline in serum PSA levels when the subjects were on high soy diet (two servings of soy per day) (82). Another phase II trial with isoflavones reported a significantly lowered PSA slope in the intervention group supporting an effect of isoflavones on PSA (83).…”

Phytoestrogens and their Potential Role in Prostate Cancer Prevention and Treatment

“…However, a few studies conducted in subjects with high baseline PSA revealed a decrease in the PSA level while on soy supplementation [63]. Data from a randomized crossover study performed by Maskarinec et al [59] in 23 healthy men with a mean age of 58 years revealed a 14% statistically significant decline in PSA with no change in testosterone level when the subjects were given a high soy diet compared with a low soy diet. A randomized controlled trial done by Ide et al [60] in Japenese men (n=85) with a median age of 73 years showed that PSA levels significantly decreased in the supplement treated group (isoflavones 40 mg plus curcumin 100 mg daily for 6 months) only in those subjects with a baseline PSA level greater than 10 ng/ml, with no prostate cancer.…”

Dietary Manipulation for Therapeutic Effect in Prostate Cancer

“…One randomized, placebocontrolled trial of 12 weeks treatment with genistein in men with early prostate cancer found no significant difference in PSA levels between the treatment and placebo groups (Kumar et al, 2004), although the authors suggested that surrogate measures were being affected by treatment. Other trials support the idea that isoflavones, even given over relatively short periods of time, can possibly slow the rate of rise of PSA, though no statistically significant conclusions can be drawn (Dalais et al, 2004;Hussain et al, 2003;Maskarinec et al, 2006;Pendleton et al, 2008 (Davis et al, 2000;Takahashi et al, 2006;Tepper et al, 2007) b. c. d. (Nakamura et al, 2002;Tsui et al, 2008 (Davis et al, 1998) b. (Palozza et al, 2010) c. (Benitez et al, 2007;Kuwajerwala et al, 2002) d. (Davis et al, 1998;Lian et al, 1998) c. (Benitez et al, 2007;Kuwajerwala et al, 2002;Mitchell et al, 1999) d. (Bhatia & Agarwal, 2001;Kazi et al, 2003;Rice et al, 2007) c. (Benitez et al, 2007;Kuwajerwala et al, 2002) d. Protein tyrosine kinase a. Inhibition of EGF tyrosine kinase activation by genistein c. Resveratrol inhibits tyrosine kinase d. Curcumin inhibits EGF-R signaling a.…”

“…As the studies in Table 3 Non -significant decline in testosterone levels, but compensated rise in LH levels (Rannikko et al, 2006) High or low soy diet for 3 months N=24, randomized crossover to alternative diet after 1 month washout Decline of PSA (not significant) of 14% while on high soy diet (Maskarinec et al, 2006) Lycopene with or without soy isoflavones for 6 months N=71, includes hormone sensitive and resistant patients. Randomized trial.…”