One study says soy isoflavones don't help hot flashes, another study says they do

By David Liu, Ph.D.

Tuesday Aug 9, 2011 (foodconsumer.org) -- A new trial in the Aug 8, 2011 issue of Archives of Internal Medicine suggests taking a soy ingredient called isoflavone does not help menopausal women.

Menopausal women often experience hot flashes among other things. Many women eat soy products or take isoflavone supplements to relieve their menopausal symptoms.

Silvina Levis MD and colleagues of Miami Veterans Affairs Healthcare System received a grant from the U.S. government to conduct the randomized, double blind trial only to find that soy isoflavone supplements do not help bone loss and hot flashes.

Even worse, the authors actually found women who used soy isoflavones were more likely to experience hot flashes, and constipation than women in the control group.

The results were derived from data collected  after the two-year dietary supplementation trial of 248 women aged 45 to 60 who were enrolled in the trial from July 1, 2004 through March 31, 2009.

In the trial, 200 mg per day of soy isoflavones was given to the women in the study group.   A dose of 200 mg per day of soy isoflavones is a lot and eating soy foods generally can't provide so much.

It is unknown how many women were able to take soy isoflavones on a daily basis. This can affect the outcome of the trial.

The researchers concluded that "in this population, the daily administration of tablets containing 200 mg of soy isoflavones for 2 years did not prevent bone loss or menopausal symptoms."

The study was inconsistent with some previous studies.

Published in the Nov. 2010 issue of Maturitas, a trial by L.O. Carmignani of the State University of Campinas in Campinas, SP, Brazil and colleagues suggests that "dietary soy supplementation may constitute an effective alternative therapy for somatic and urogenital symptoms on the menopause."

Women also ages 40 to 60 in this randomized, double blind, and controlled trial were given 90 mg per day of isoflavones or 1 mg estradiol and 0.5 mg norethisterone acetate or placebo for 16 weeks.

Both the soy isoflavone group and the hormone user group experimenced an improvement in somatic and urogenital symptoms during the treatment while the placebo controls did not.

Both hormone users and soy isoflavone users had their somatic  symptoms (hot flashes and muscle pain among other things) reduced by 45.6 percent and 49.8 percent, respectively.

Hormone treatment and soy isoflavone supplementation both reduced urogenital symptoms such as vaginal dryness by 38.6 and 31.2 percent respectively.

Why could these two trials differ so much? Could the dose used by US researchers be too high? or the U.S. trial lasted too long?  Or maybe the difference is due to some undiscovered bias in either or both of the trials?

One thing that affect the outcome for sure is the study population.  Results from one population in one region may not be applicable to another in another region or country.

In any case, menopausal women who have some menopausal symptoms may want to give soy supplements or whatever alternative treatment a try before they settle with the risky hormone therapy.  Endogenous or naturally identical estrogen or other hormones can be much much more dangerous than phytochemicals with estrogenic properties like those found in soybeans.

Make an informed decision as to what can be used to help relieve menopausal symptoms.