For years, researchers have been exploring the potential of soy isoflavones — naturally-occurring plant estrogens — for alleviating menopausal symptoms such as hot flashes, atrophy and bone loss. Thus far, certain components of soy, including genestein and S-equol have shown the most promise. However, are they safe? And, as the adoption of soy as a viable alternative to risk-ridden hormone replacement therapy continues to grow, and women turn to supplements rather than food-based soy, is there anything that they need to worry about in terms of side effects?
Researchers recently evaluated this question in a study of 403 postmenopausal women who took either 80 mg soy tablets, 120 mg soy tablets or placebo tablet daily for two years. The particular type of soy isoflavones used were hypocotyl isoflavones, which are a byproduct of soy protein and (very rich in daidzein – the second most plentiful isoflavone in soy. The effects of the supplements were measured at the study’s start, at one year and at the end via blood tests and a well-woman examination (i.e. mammogram, pap smear, x-rays to measure bone density). A smaller group of women also had ultrasounds done to determine any possible effects on the lining of the uterus or development of fibroids.
Although the primary goal of the study was to determine the effects of this type of soy supplement on osteoporosis and bone loss, the researchers discovered that taking soy supplements during this time period did not present any major risk to health and did not affect thyroid function. Although one participant developed breast cancer during the study and one, endometrial cancer, 1) utrasounds in the subgroup of women who received them did not show any uterine thickening and 2) the rate of cancer development in this study, only two women over a two year time period, was considerably lower than statistically likely in a general population of women. Both of these factors support the contention that soy isoflavones are not likely to promote either cancers.
So, is soy safe over the long-term? It appears that it is. HOWEVER, bear in mind that the type of soy used in this study is are very different that the type that is commonly sold over the counter, which commonly contain higher percentages of genistein, the most plentiful isoflavone component in soy.
And what about osteoporosis? This particular paper did not address those specific results, although others have. Thus far, the results have been mixed. However, this particular study, better known as OPUS (Osteoporosis Prevention Using Soy)is one of the largest and most comprehensive to date and those findings are likely to come to light soon.
In the interim, if you are going to be taking soy in supplement form, be mindful that your exposure is likely to be as one to four times that a typical Asian diet and as much as 100 times that of a typical Western diet. While these level do not appear to be harmful, herbal and plant medicines are not without risk so as always, the rule of thumb is be vigilant and speak to a health practitioner first.