Does phytoestrogen supplementation improve cognition in humans? A systematic review

Recent evidence indicates that resveratrol, a phytoestrogen, can improve cognitive function in postmenopausal women by enhancing cerebral vasodilator responsiveness. We examine the effects of phytoestrogen supplementation on cognition and compare resveratrol with other phytoestrogens. Databases were searched for reports of randomized controlled trials (RCTs) containing terms describing phytoestrogens together with terms relating to cognition. Effect sizes were determined for changes in cognition. We identified 23 RCTs, 15 with isoflavone and eight with resveratrol or grape formulations. Six soy isoflavone studies showed positive cognitive effects of medium size. Greater benefits were seen in women who were <10 years postmenopausal and supplemented for <6 months. Small-to-medium effect-size cognitive benefits of resveratrol were seen in four studies of older adults of mixed gender and in postmenopausal women who took 150-200 mg resveratrol daily for at least 14 weeks. No benefits were seen in three studies using red clover or grape formulations. Supplementation with either soy isoflavone or resveratrol improved executive function and memory domains of cognitively normal older adults in half of the included studies, mostly with medium effect sizes. The cognitive benefit of resveratrol was related to improved cerebral perfusion.