The purpose of this analysis was to determine whether soy isoflavones were effective in the alleviation of hot flashes in perimenopausal and postmenopausal women. Two large data bases, PubMed and the Cochrane Controlled Clinical Trials Register Database were searched for studies on this topic that were double-blind randomized controlled trials through mid December 2010. A total of 19 trials met the criteria for inclusion in this systematic review and another 17 trials were selected for their meta-analyses on the role of soy isoflavones on hot flash frequency and severity. An analysis of these 36 publications revealed that ingesting soy isoflavones, at an average of 54 mg per day for 6 weeks to 12 months did significantly reduce the frequency of hot flashes by 20.6% when compared with individuals taking placebo. When soy isoflavones were delivered in a supplement form providing an average of 18.8 mg of the isoflavone constituent genistein, the results were more than twice as effecting at reducing frequency of hot flashes than supplements with lower amounts of genistein. The authors concluded that whether or not soy isoflavone supplements were extractions of soybeans or chemically synthesized products, they were more effective than placebo in reducing the frequency and severity of hot flashes.
The effects of soy isoflavones have been studied in oh so many ways– heart disease, osteoporosis, diabetes, numerous cancers, hot flashes and more. From the hundreds of studies that were reviewed, North American Menopause Society position statement of October 2010 on the role of isoflavones in menopausal health reported that soy isoflavones are modestly effective in relieving menopausal symptoms. They also concluded that soy food consumption is associated with lower risk of breast and endometrial cancer and that the effectiveness of soy isoflavones on bone has yet to be proven and the role of soy in cardiovascular benefits is still unclear to draw any strong conclusions.
The results of the current review and meta-analysis of randomized controlled trials shows that about 54 mg of soy isoflavones per day or 18.8 mg of genistein per day has a modest effect on reducing the severity and frequency of hot flashes. For some women, this will be just enough to satisfy them, or warrant inclusion in their total treatment plan to alleviate hot flashes. I have found in my practice that supplementing with soy isoflavones can then be used with herbal products and/or hormone therapy, but lower doses of those may then be needed due to the partial improvement with the soy isoflavones.
Taku K, Melby M, Kronenberg F, Kurzer M, Messina M. Extracted or synthesized soybean isoflavones reduce menopausal hot flash frequency and severity: systematic review and meta-analysis of randomized controlled trials. Menopause 2012; 19(7):776-790.