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Just How Effective is Soy for Bones & Menopause?

Posted Aug 09 2011 8:30am
Ever since the first analysis of the Women's Health Initiative was published 9 years ago, the tide has turned against hormone replacement therapy.  What we used to consider tossing into the drinking water is now considered anathema.  Medically speaking, we've even gone so far as to now label this as hormone therapy, to indicate that it's not necessarily for replacement purposes.  Personally, this still reminds me of Shakespeare's words regarding roses.

Regardless of whether one believes there's a difference between conjugated equine estrogens and bio-identical estradiol (also available from Big Pharma as Vivelle Dot & Climara among others) and between the synthetic progestin, medroxyprogesterone acetate (MPA), and bio-identical progesterone, there has also been a parallel move to consider alternative solutions such as red clover, black cohosh and even soy.  However, these options have not been without controversy, nor have they been supported by randomized double blind placebo controlled evidence.

However, in an analysis of Soy Phytoestrogens As Replacement Estrogen (SPARE) published yesterday in Archives of Internal Medicine , the authors concluded that daily administration of 200mg of soy isoflavones for 2yrs did not improve menopausal symptoms nor prevent bone loss.  In an attempt to remove the usual sources of bias, it should be noted that this study was supported by the National Institutes of Health, rather than a nutraceutical manufacturer (although I suppose one could hypothesize that the NIH is in cahoots w/Big Pharma against the use of natural herbs & supplements).  
Furthermore, this was a randomized, placebo-controlled, double-blind study of 248 menopausal women avg 52-53yo, all within 5 years of menopause, unlike the participants in WHI who were 65yo and 10yrs past menopause on average.  Finally, to deal with another source of limitation from prior studies, one needs to know that the average American (and western European) consumes less than 3mg of soy isoflavones daily while the average Chinese & Japanese consume 25-50mg/d w/less than 5% consuming >100mg/d, in order to understand the significance of the SPARE participants being randomized to 200mg daily vs placebo.

After two years of study, the authors noted no difference in bone mineral density between those randomized to soy isoflavones vs placebo.  Both groups lost equal amounts of bone at all sites measured, eg spine, total hip & femoral neck.  Interestingly enough, a statistically significantly larger proportion of women randomized to soy isoflavone complained of vasomotor instability compared with those randomized to placebo.  There was also an increase in constipation in those randomized to soy isoflavones but this did not reach statistical significance.

The editorialists noted that given the multitude of observational and RCT studies demonstrating no benefit from soy, we really need to look for other treatment options for symptomatic women, perhaps focusing on the individual symptoms, such as disturbances to sleep and mood, rather than pinning all our hopes on a single hormone.   USA Today had a rather nice write up about this study - the only problem I had was their tendency not to differentiate between non-bio-identical and bio-identical.  This was most glaring when they stated that progesterone was used in WHI when in fact it was MPA, a medication know to have dramatically different physiologic effects than its bio-identical counterpart.
One last thought - this study is about soy isoflavone supplements, not edamame, which is a good source of fiber & protein.  Just be sure to keep tract of your estradiol levels . . .

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