In a past blog, Natural Medications (Herbs, Vitamins, and Supplements) for Menopausal Symptoms, I discussed the data supporting a trial of isoflavones in women with menopausal symptoms. However, there was not a lot of data. Now, Medscape is reporting, “Isoflavones may reduce insomnia symptoms” in postmenopausal women, according to a small study in the journal Menopause.
The researchers evaluated “sleep parameters” in 38 postmenopausal women with insomnia and then measured the parameter changes “during treatment with isoflavones.”
For the isoflavones group, polysomnography showed sleep efficiency “increased significantly” (from 77.9% to 83.9%) compared to the placebo group (77.6% to 81.2%).
In addition, initial insomnia percentages of 89.5% in the isoflavones group, dropped to 36.9% by the end of the study. Isoflavones were also “effective in reducing the number of hot flashes” in the study population, but only significantly after about four months of treatment.
The North American Menopause Society (NAMS) consensus recommendation says: “In women who need relief for mild vasomotor symptoms, (we recommend) first considering lifestyle changes, either alone or combined with a nonprescription remedy, such as dietary isoflavones or black cohosh …”
Also, the Natural Medicines Comprehensive Database (NMCD) says, “Soy has the most evidence for effectiveness and may be worth trying for some women. Soy foods are preferred over soy supplements which have concentrated isoflavones.” Another review states: “Less is known about the safety of soy supplements.”
Here’s what I’ve written in the past about soy isoflavones:
Phytoestrogens
The most commonly used group of natural products for vasomotor symptoms are phytoestrogens or “plant estrogens.” The three mains kinds are:

• isoflavones,
• lignans, and
• coumestans.

Isoflavones are the most potent and the most common in supplements. Phytoestrogens are also found in many common food sources. Foods containing phytoestrogens are probably safe, but advise patients with breast cancer concerns to avoid excessive consumption of these foods or concentrated phytoestrogen supplements.
Soy (Glycine max) and soy isoflavones are the most commonly used phytoestrogens … and the best studied.
A NMCD review concludes, “Consuming soy protein, 20 to 60 grams per day, containing 34 to 76 mg of isoflavones, seems to modestly decrease the frequency and severity of hot flashes in menopausal women.” Soy extracts in tablet form, providing 35-150 mg of isoflavones daily, also seems to have beneficial effects. Soy supplements appear to be helpful in about 30% of postmenopausal women.”
One review concluded that isoflavone preparations seemed to be less effective than soy foods.
However, a 2005 systematic review of soy was less positive: “The available evidence suggests that phytoestrogens available as soy foods (and) soy extracts… do not improve hot flushes or other menopausal symptoms … Of the 8 soy food trials reporting hot flush frequency outcomes, 7 were negative.
Of the 5 soy extract trials reporting hot flush frequency, 3 (including the 2 largest trials) were negative.
According to the NMCD, “The reason for these conflicting findings is not clear. But it may be due to high placebo response rates in some trials. Patient expectations of treatments can significantly impact perceived benefits.”
Nevertheless, NAMS recommends “for women with frequent hot flashes, clinicians may consider recommending soy foods or soy isoflavone supplements. Most hot flash studies used isoflavone amounts of 40 to 80 mg/day … Effects, if any, may take several weeks.”
“Isoflavones exhibit a low incidence of side effects, although caution is advised when estrogenicity is a concern,” the American College of Obstetricians and Gynecologists (ACOG) concludes. The go on to say, “Soy and isoflavones may be helpful in the short-term (<2 years) treatment of vasomotor symptoms.”
NAMS adds, “Soy and isoflavone intake over prolonged periods may improve lipoprotein profiles and protect against osteoporosis. Soy in foodstuffs may differ in biological activity from soy and isoflavones in supplements.”
When ConsumerLab.com (an independent quality testing lab that requires a subscription to access their full test results ) tested soy isoflavones in 2005, two of twelve supplements failed testing because they contained, respectively, 50% and 59% of their listed total isoflavones and were low in specific isoflavones (daidzin/daidzein and glycitin/glycitein).
A soy/red clover isoflavone product also failed because it would not break apart properly, suggesting that some of its ingredients might pass through the body unused. The other products passed the testing — they contained their key ingredients, had no contaminants, and broke apart properly for absorption.
Some women might ask about ipriflavone. It’s a synthetic soy derivative. Some research suggests that it reduces bone loss. But, unfortunately, it does not have any effect on hot flashes.
Some research suggests that constituents in soy, genistein and daidzein, may stimulate existing breast tumor growth and antagonize the effects of tamoxifen. The NMCD says, “Tell women with breast cancer who take tamoxifen not to use soy.”
Breast cancer survivors often have significant problems with hot flashes. Although soy seems to be helpful for some with hot flashes, it doesn’t seem to be effective for women who have hot flashes related to breast cancer treatment. Caution patients on warfarin to be cautious about adding soy to their diet. Soy can reduce the international normalized ratio (INR) and decrease warfarin effectiveness.