The effects of soy isoflavones on total testosterone and follicle-stimulating hormone levels in women with polycystic ovary syndrome: a systematic review and meta-analysis

Objectives: The aims of this systematic review and meta-analysis were to evaluate the effectiveness of soy isoflavones on serum levels of total testosterone (TT) and follicle-stimulating hormone (FSH) in women with polycystic ovary syndrome (PCOS). Methods: A meta-analysis was performed by searching for relevant randomised controlled trials (RCTs) in several databases. Of the four trials found, the eligibility criteria to evaluate the efficacy of soy isoflavones on serum levels of FSH were met by three trials and of TT by four trials. The Cochrane scale was used to evaluate the risk of bias. Fixed-effects and random-effects models were used to evaluate overall effect. The chi(2) test (Cochran's Q test) and the I-2 index were used to assess the heterogeneity of RCTs. Results: Our results showed that soy isoflavones significantly decreased TT (weighted mean difference [WMD] - 0.14; 95% confidence interval [CI] - 0.2, -0.02; p = 0.016; I-2 = 89%, p < 0.001) but had no significant effect on FSH levels (WMD -0.25; 95% CI -0.54, 0.02; p = 0.06; I-2 = 0%, p = 0.85). Conclusion: Although the results of this meta-analysis showed that soy isoflavones in women with PCOS decreased TT and had no significant effect on FSH, better and more valid studies are needed to confirm these results.