The ability of isoflavones and soy products to alleviate menopausal hot flashes has been researched for more than 25 years,1 and yet, questions about efficacy remain. In the past 5 years, many published reviews and clinical trials have evaluated the efficacy of isoflavones. The evidence overall justifies the use of isoflavones for the alleviation of menopausal symptoms.
One issue that complicates the interpretation of the scientific literature is the failure of many technical reviews and meta-analyses to sub-analyze the data according to the type of supplement used (few trials use soyfoods because they make blinding difficult) in the clinical trials. In 2012, supplements that have a relative isoflavone concentration similar to whole soybeans (genistein>daidzein>>glycitein) were found to be significantly more efficacious than supplements derived from soy germ, which have a different isoflavone concentration (daidzein>glycitein>>genistein) than whole soybeans.2
Quotations from reviews published since 2016:
“In total, we could see that genistein and S-equol could significantly improve hot flashes. Additionally, soy isoflavone might also have beneficial effects on these symptoms.”3
“In the literature we reviewed, isoflavones reduce hot flashes even accounting for placebo effect …”.4
“In particular, literature show that a specific dosage of isoflavones … might improve menopausal symptoms, particularly in reducing the frequency of hot flashes (from 50-120mg/day) …”5
“… isoflavones could be useful in reducing hot flushes associated with menopause.”6
Quotations from clinical trials published since 2017:
“Soy germ extract with 100mg of isoflavone glycosides was shown to modestly, but significantly, reduce menopausal hot flushes.”7
“Soy drink consumption had no effect on cognitive function in post-menopausal women. Consumption of ~ 350ml/day (35mg Ifs [isoflavones]) for 12 weeks significantly reduced VMS [vasomotor symptoms] in those with more severe symptoms at baseline.”8
“Effects of isoflavone on frequency and severity of hot flushes in perimenopausal women is observed.”9
“Soy isoflavone improves the MRS [menopause rating scale] score among both the perimenopausal and postmenopausal women. As they are most effective for somatic and psychological symptoms, their use could be beneficial during perimenopause.”10
“In a randomized, double-blind, placebo-controlled trial postmenopausal women were randomly given either soybean (Soygan 500mg capsule; n = 60), or omega-3 fatty acids (Omega-rex 1000mg soft gel; n = 60), or placebo (n = 60) daily for 12 weeks … Soygan and Omega-rex reduced the MRS [menopause rating scale] score and improved menopausal symptoms in postmenopausal women.”11
“The consumption of a cereal bar containing phytoestrogens was able to improve the symptoms of climacteric syndrome.”12
“There were reduced menopausal symptoms between baseline and follow-up for vasomotor [symptoms] …There were no between-group differences for dose for vasomotor [symptoms].”13
“The intervention, a proprietary combination of soy isoflavone, black cohosh, chasteberry and evening primrose oil extracts, and the placebo, were administered to each group for total of 12 weeks … These data indicate that a nutraceutical containing a combination of four medicinal herbs effectively and safely improved menopausal symptoms14
It is evident from the above studies that isoflavones continue to be evaluated as agents for use in the alleviation of menopausal symptoms. Of the 8 trials cited above, only 1 failed to observe that isoflavones alleviated hot flashes,13 but in two of these, isoflavones were combined with other bioactives.12,14 In one case, isoflavones were combined with lignans12 and in the other, they were combined with black cohosh, chasteberry, and evening primrose oil extracts.14 Furthermore, in one study, it is not possible to determine from the information provided in the manuscript the precise makeup of the intervention product, although it was derived from soybeans.11
Despite the extensive research that has been conducted, it may not be possible to reach a definitive conclusion about the efficacy of isoflavones for alleviating hot flashes. However, the evidence does justify recommending isoflavones for such purpose for women who do not want to use hormone therapy. This recommendation is especially justified because unlike hormone therapy,15 isoflavones do not increase in vivo breast cell proliferation,16 a marker of breast cancer risk. Most isoflavones trials have intervened with 50-100mg/day.
- Murkies AL, Lombard C, Strauss BJ, et al. Dietary flour supplementation decreases post-menopausal hot flushes: effect of soy and wheat. Maturitas. 1995;21:189-95.
- Taku K, Melby MK, Kronenberg F, et al. Extracted or synthesized soybean isoflavones reduce menopausal hot flash frequency and severity: systematic review and meta-analysis of randomized controlled trials. Menopause. 2012;19:776-90.
- Guo PP, Li P, Zhang XH, et al. Complementary and alternative medicine for natural and treatment-induced vasomotor symptoms: An overview of systematic reviews and meta-analyses. Complement Ther Clin Pract. 2019;36:181-94.
- Chen LR, Ko NY, Chen KH. Isoflavone supplements for menopausal women: A systematic review. Nutrients. 2019;11.
- Perna S, Peroni G, Miccono A, et al. Multidimensional effects of soy isoflavone by food or supplements in menopause women: A systematic review and bibliometric analysis. Nat Prod Commun. 2016;11:1733-40.
- Gomez-Zorita S, Gonzalez-Arceo M, Fernandez-Quintela A, et al. Scientific evidence supporting the beneficial effects of isoflavones on human health. Nutrients. 2020;12.
- Imhof M, Gocan A, Imhof M, et al. Soy germ extract alleviates menopausal hot flushes: placebo-controlled double-blind trial. Eur J Clin Nutr. 2018;72:961-70.
- Furlong ON, Parr HJ, Hodge SJ, et al. Consumption of a soy drink has no effect on cognitive function but may alleviate vasomotor symptoms in post-menopausal women; a randomised trial. Eur J Nutr. 2020;59:755-66.
- Vahid Dastjerdi M, Eslami B, Alsadat Sharifi M, et al. Effect of soy isoflavone on hot flushes, endometrial thickness, and breast clinical as well as sonographic features. Iranian journal of public health. 2018;47:382-9.
- Ahsan M, Mallick AK. The effect of soy isoflavones on the menopause rating scale scoring in perimenopausal and postmenopausal women: A pilot study. J Clin Diagn Res. 2017;11:FC13-FC6.
- Purzand B, Rokhgireh S, Shabani Zanjani M, et al. The comparison of the effect of soybean and fish oil on supplementation on menopausal symptoms in postmenopausal women: A randomized, double-blind, placebo-controlled trial. Complement Ther Clin Pract. 2020;41:101239.
- Frigo M, de Barros E, Dos Santos PCB, et al. Effects of a cereal bar with a combination of phytoestrogens on the climacteric symptoms: A placebo-controlled, randomized trial. J Am Coll Nutr. 2021:1-8.
- Simpson EEA, Furlong ON, Parr HJ, et al. The effect of a randomized 12-week soy drink intervention on everyday mood in postmenopausal women. Menopause. 2019;26:867-73.
- Rattanatantikul T, Maiprasert M, Sugkraroek P, et al. Efficacy and safety of nutraceutical on menopausal symptoms in post-menopausal women: A randomized, double-blind, placebo-controlled clinical trial. Journal of dietary supplements. 2020:1-15.
- Conner P, Soderqvist G, Skoog L, et al. Breast cell proliferation in postmenopausal women during HRT evaluated through fine needle aspiration cytology. Breast Cancer Res Treat. 2003;78:159-65.
- Khan SA, Chatterton RT, Michel N, et al. Soy isoflavone supplementation for breast cancer risk reduction: A randomized phase II trial. Cancer Prev Res (Phila). 2012;5:309-19.