soy isoflavones and your brain

Soy Isoflavones

  • Food & Drink
  • Updated June 19, 2018

Soy isoflavones are polyphenols found in soy products and other plants. They preferentially interact with a type of estrogen receptor involved in cognitive functions. Because they interact with estrogen receptors, soy isoflavones have also been studied for preventing menopausal symptoms and premenstrual syndrome. Some clinical studies have suggested that soy isoflavone treatments may improve a few cognitive functions, though the benefits appear to depend on age, gender, and ethnicity. Soy isoflavone intake via diet or supplementation is generally regarded as safe.

Evidence

Numerous randomized controlled trials have tested the effects of soy isoflavones, though results appear to depend on age, gender, and ethnicity. Our search identified:

  • 1 meta-analysis based on 10 randomized controlled trials
  • 7 clinical trials testing soy isoflavones (1 in Alzheimer's patients and the others in postmenopausal women)
  • Numerous preclinical studies on possible mechanisms of action

Potential Benefit

Clinical studies of soy isoflavones suggest they benefit some cognitive functions, though benefits appear to vary by age, gender, and region [1]. A large meta-analysis of 10 randomized controlled trials reported that soy isoflavone supplementation significantly improved overall cognitive function and visual memory in people under 60 years old from non-US countries [2].

In a large double-blind randomized controlled trial of postmenopausal women, treatment with isoflavone-rich soy protein for several years improved visual memory, but not other cognitive functions compared to control [3]. More benefits were seen in women between 5–10 years of menopause than those 10 years post-menopause. Other smaller randomized controlled trials in postmenopausal women reported that isoflavone treatment improved episodic memory, attention, and category fluency, but not nonverbal memory, category generation, planning, or rule-learning [4][5].

In older men and women, soy isoflavones treatment resulted in improved spatial memory and construction, verbal fluency, and dexterity, but worse executive function [6]. In young healthy adults, high soy diet for 10 weeks resulted in significant improvements in short-term and long-term memory and in mental flexibility, but not in attention or category generation compared to those in the control diet [7]. Women, but not men, on the high soy diet also improved in letter fluency and planning.

Soy isoflavones bind to an estrogen receptor called ERβ, which is expressed in brain regions important for executive function and memory and in preclinical models can lead to improved cognitive functions [8][9]. Soy isoflavones also exhibit antioxidant and anti-inflammatory activities [10]. See Genistein rating for more details on this specific soy isoflavone.

APOE4 Carriers:

In a randomized controlled trial of 59 people with Alzheimer's disease, APOE4 genotype did not affect the response to soy isoflavone treatment [11]. For more information on what the APOE4 gene allele means for your health, read our APOE4 information page.

For Dementia Patients

A randomized controlled trial of 59 Alzheimer's disease patients reported that soy isoflavone treatment (100 mg/day) for 6 months did not significantly improve cognitive function over placebo, despite increased plasma levels of isoflavones [11].

Safety

Soy isoflavones are generally considered safe [12]. Numerous randomized controlled trials in menopausal women reported that side effects were not significantly different between soy isoflavone and placebo groups [2][13]. Adverse events were generally mild [3] and included gastrointestinal and musculoskeletal complaints [2]. One systematic review of over 100 studies in patients with or at risk of breast cancer suggested that while there is no clear evidence of harm, better evidence confirming safety is required before use of high dose (over 100 mg/day) isoflavones can be recommended for breast cancer patients [14]. Drug interactions with soy isoflavones are not well-documented [15], but because they bind to estrogen receptors, it may 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.

How to Use

Soy isoflavones are present in soybeans, tofu, fava beans, and other plants. It is also available as a supplement in tablet and capsule forms. Doses that showed improvement in some cognitive functions in clinical studies ranged from 60–100 mg/day [4][6][7].

Learn More

Evaluation of soy isoflavones' potential biological effects from Examine.com

Quality Control of Sources: United States Pharmacopeial Convention (USP) and FDA Information on Dietary Supplements offer information on the quality of specific supplements and can assist in finding a trusted brand.

References

  1. North American Menopause S (2011) The role of soy isoflavones in menopausal health: report of The North American Menopause Society/Wulf H. Utian Translational Science Symposium in Chicago, IL (October 2010). Menopause 18, 732-753.
  2. Cheng PF, Chen JJ, Zhou XY et al. (2015) Do soy isoflavones improve cognitive function in postmenopausal women? A meta-analysis. Menopause 22, 198-206.
  3. Henderson VW, St John JA, Hodis HN et al. (2012) Long-term soy isoflavone supplementation and cognition in women: a randomized, controlled trial. Neurology 78, 1841-1848.
  4. Duffy R, Wiseman H, File SE (2003) Improved cognitive function in postmenopausal women after 12 weeks of consumption of a soya extract containing isoflavones. Pharmacol Biochem Behav 75, 721-729.
  5. Kritz-Silverstein D, Von Muhlen D, Barrett-Connor E et al. (2003) Isoflavones and cognitive function in older women: the SOy and Postmenopausal Health In Aging (SOPHIA) Study. Menopause 10, 196-202.
  6. Gleason CE, Carlsson CM, Barnet JH et al. (2009) A preliminary study of the safety, feasibility and cognitive efficacy of soy isoflavone supplements in older men and women. Age Ageing 38, 86-93.
  7. File SE, Jarrett N, Fluck E et al. (2001) Eating soya improves human memory. Psychopharmacology (Berl) 157, 430-436.https://www.ncbi.nlm.nih.gov/pubmed/11605103
  8. Zhao L, Brinton RD (2005) Structure-based virtual screening for plant-based ERbeta-selective ligands as potential preventative therapy against age-related neurodegenerative diseases. J Med Chem 48, 3463-3466.
  9. Turner JV, Agatonovic-Kustrin S, Glass BD (2007) Molecular aspects of phytoestrogen selective binding at estrogen receptors. J Pharm Sci 96, 1879-1885.
  10. Kalaiselvan V, Kalaivani M, Vijayakumar A et al. (2010) Current knowledge and future direction of research on soy isoflavones as a therapeutic agents. Pharmacogn Rev 4, 111-117.
  11. Gleason CE, Fischer BL, Dowling NM et al. (2015) Cognitive Effects of Soy Isoflavones in Patients with Alzheimer's Disease. J Alzheimers Dis 47, 1009-1019.
  12. Munro IC, Harwood M, Hlywka JJ et al. (2003) Soy isoflavones: a safety review. Nutr Rev 61, 1-33.
  13. Chen MN, Lin CC, Liu CF (2015) Efficacy of phytoestrogens for menopausal symptoms: a meta-analysis and systematic review. Climacteric 18, 260-269.
  14. Fritz H, Seely D, Flower G et al. (2013) Soy, red clover, and isoflavones and breast cancer: a systematic review. PLoS One 8, e81968.
  15. Soy. Drugs.com.