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. SYSTEMATIC REVIEW REGISTRATION PROSPERO registration no. CRD42018082070.