Effects of soy isoflavones on cognitive function: a systematic review and meta-analysis of randomized controlled trials

Context: The results of preclinical and observational studies support the beneficial effect of soy isoflavones on cognition. Objective: This review aimed to evaluate the effects of soy isoflavones on cognition in adults. Data Sources: The PUBMED, EMBASE, Ovid Medline, Cochrane Library, and clinicaltrials.gov databases were searched. Study Selection: Two researchers independently screened 1955 records, using the PICOS criteria: participants were adults; intervention was dietary sources with soy isoflavones or isolated soy isoflavones; comparator was any comparator; outcome was cognitive function; study type was randomized controlled trials (RCTs). A third researcher was consulted to resolve any discrepancies. Sixteen RCTs were included and their quality assessed. Data Extraction: Information on study design, characteristics of participants, and outcomes was extracted. PRISMA guidelines were followed. Data Analysis: A random-effects meta-analysis was used to pool estimates across studies. In the 16 RCTs (1386 participants, mean age = 60 y), soy isoflavones were found to improve overall cognitive function (standardized mean difference [SMD], 0.19; 95% confidence interval [CI], 0.07-0.32) and memory (SMD, 0.15; 95%CI, 0.03-0.26). Conclusion: The results showed that soy isoflavones may improve cognitive function in adults.