Genistein is a type of isoflavone (i.e., polyphenol) found in soy products. It preferentially acts on an estrogen receptor thought to play important roles in cognitive functions, menopausal symptoms, and premenstrual syndrome. No studies have tested genistein specifically for preventing cognitive decline, but studies of soy isoflavone treatments that included genistein did find benefit in some cognitive functions for people of specific ages and genders. Genistein intake via diet or supplementation is generally regarded as safe.
No clinical trial has tested genistein specifically, though numerous trials have examined the effects of soy isoflavone treatments that included genistein. Our search identified:
No clinical trials have tested genistein specifically, though some studies have examined the effects of soy isoflavone treatments in menopausal women (see Soy Isoflavones rating for details).
An observational study of 195 Japanese and 185 Chinese women reported that dietary intake of genistein was not significantly associated with measures of cognitive performance in either ethnic group .
Genistein binds to an estrogen receptor called ERβ, which is expressed in brain regions important for executive function and memory . Cognitive benefits of genistein have been observed in preclinical models of brain toxicity , inflammation , diabetes-induced cognitive decline , Parkinson's disease , and Alzheimer's disease . In these studies, genistein inhibited cell death , increased levels of a protein that protects brain cells , decreased levels of the enzyme that breaks down the neurotransmitter? acetylcholine , lowered inflammation , and prevented mitochondrial dysfunction . In preclinical models of Alzheimer's disease, genistein decreases beta-amyloid? levels  and inhibits death of neurons induced by beta-amyloid . These effects have not been confirmed in humans.
No studies have tested genistein specifically in dementia patients. A randomized controlled trial of 59 Alzheimer's disease patients reported that soy isoflavone treatment (100 mg/day) for six months did not significantly improve cognitive function over placebo, despite increased plasma levels of isoflavones .
Genistein is generally considered safe, but most safety data come from large studies with soy isoflavones or dietary consumption of soy products. The largest study that examined genistein specifically was a meta-analysis of seven randomized controlled trials including a total of 670 subjects . In trials lasting two to three years, about 19% of subjects reported gastrointestinal symptoms. Although genistein acts on estrogen receptors, several studies including one lasting three years reported that genistein is not associated with any significant adverse effect on breast density, the uterus, or endometrial thickness. Drug interactions with genistein are not well-documented , but because genistein binds to estrogen receptors, it will likely interact with drugs that target the estrogen system.
NOTE: This is not a comprehensive safety evaluation or complete list of potentially harmful drug interactions. It is important to discuss safety issues with your physician before taking any new supplement or medication.
Genistein is found in soybeans, tofu, and fava beans . It is also available as supplements in tablet and capsule forms. Doses that showed improvement in a few cognitive functions in clinical studies ranged from 60–100 mg of soy isoflavones a day, which contains genistein doses of ~52 mg/day . Genistin, a sugar-bound soy isoflavone that is biologically inactive, can be broken down into a bioavailable form in our digestive tract after exposure to high temperatures, such as cooking .
A randomized controlled trial is testing the effects of genistein treatment on amyloid beta levels in the cerebral spinal fluid of Alzheimer’s disease patients.