The theme of the Upcoming Grand Rounds held at June 21th (1st day of the Summer) at Shrink Rap is “hot”. A bit far-fetched, but aah you know….shrinks“. Of course they
hope assume that we will express Weiner-like exhibitionism at our blogs. Or go into spicy details of hot sexpectations or other Penis Friday NCBI-ROFL posts. But no, not me, scientist and librarian to my bone marrow. I will stick to boring, solid science and will do a thorough search to find the evidence. Here I will discuss whether soy really helps to relieve hot flashes (also called hot flushes).
…..As illustrated by this HOT picture, I should post as well…..
Yes, many menopausal women plagued by hot flashes take their relief in soy or other phytoestrogens (estrogen-like chemicals derived from plants). I know, because I happen to have many menopausal women in my circle of friends who prefer taking soy over estrogen. They rather not take normal hormone replacement therapy, because this can have adverse effects if taken for a longer time. Soy on the other hand is considered a “natural remedy”, and harmless. Probably physiological doses of soy (food) are harmless and therefore a better choice than the similarly “natural” black cohosh, which is suspected to give liver injury and other adverse effects.
But is soy effective?
I did a quick search in PubMed and found a Cochrane Systematic Review from 2007 that was recently edited with no change to the conclusions.
This review looked at several phytoestrogens that were offered in several ways, as: dietary soy (9x) (powder, cereals, drinks, muffins), soy extracts (9x), red clover extracts (7x, including Promensil (5x)), Genistein extract , Flaxseed, hop-extract and a Chinese medicinal herb.
Thirty randomized controlled trials with a total of 2730 participants met the inclusion criteria: the participants were women in or just before their menopause complaining of vasomotor symptoms (thus having hot flashes) for at least 12 weeks. The intervention was a food or supplement with high levels of phytoestrogens (not any other herbal treatment) and this was compared with placebo, no treatment or hormone replacement therapy.
Only 5 trials using the red clover extract Promensil were homogenous enough to combine in a meta-analysis. The effect on one outcome (incidence of hot flashes) is shown below. As can be seen at a glance, Promensil had no significant effect, whether given in a low (40 mg/day) or a higher (80 mg/day) dose. This was also true for the other outcomes.
The other phytoestrogen interventions were very heterogeneous with respect to dose, composition and type. This was especially true for the dietary soy treatment. Although some of the trials showed a positive effect of phytoestrogens on hot flashes and night sweats, overall, phytoestrogens were no better than the comparisons.
Most trials were small, of short duration and/or of poor quality. Fewer than half of the studies (n=12) indicated that allocation had been concealed from the trial investigators.
One striking finding was that there was a strong placebo effect in most trials with a reduction in frequency of hot flashes ranging from 1% to 59% .
I also found another systematic review in PubMed by Bolaños R et al , that limited itself only to soy. Other differences with the Cochrane Systematic Review (besides the much simpler search 😉 ) were: inclusion of more recently published clinical trials, no inclusion of unpublished studies and less strict exclusion on basis of low methodological quality. Furthermore, genestein was (rightly) considered as a soy product.
The group of studies that used soy dietary supplement showed the highest heterogeneity. Overall, the results “showed a significant tendency(?) in favor of soy. Nevertheless the authors conclude (similar to the Cochrane authors), that it is still difficult to establish conclusive results given the high heterogeneity found in the studies. (but apparently the data could still be pooled?)
- Lethaby A, Marjoribanks J, Kronenberg F, Roberts H, Eden J, & Brown J. (2007). Phytoestrogens for vasomotor menopausal symptoms Cochrane Database of Systematic Reviews (4) : 10.1002/14651858.CD001395.pub3.
- Bolaños R, Del Castillo A, & Francia J (2010). Soy isoflavones versus placebo in the treatment of climacteric vasomotor symptoms: systematic review and meta-analysis. Menopause (New York, N.Y.), 17 (3), 660-6 PMID: 20464785