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Date of release: 19 September, 2011

Soy for bone protection and vasomotor symptoms


A very recent study has investigated once again the potential benefits of soy isoflavones in regard to bone protection and vasomotor symptoms [1]. A total of 248 women aged 45–60 years within 5 years of menopause and with a bone mineral density T-score of -2.0 or higher in the lumbar spine or total hip were randomly assigned, in equal proportions, to receive daily soy isoflavone tablets, 200 mg, or placebo. After 2 years, no significant differences were found between the participants receiving soy tablets and those receiving placebo regarding changes in bone mineral density in the spine (-2.0% and -2.3%, respectively), the total hip (-1.2% and -1.4%, respectively), or the femoral neck (-2.2% and -2.1%, respectively). A significantly larger proportion of participants in the soy group experienced hot flushes and constipation compared with the control group. No significant differences were found between groups in other outcomes. These clear-cut results from an NIH-funded, double-blind, placebo-controlled, randomized study were summarized as follows: ‘The daily administration of tablets containing 200 mg of soy isoflavones for 2 years did not prevent bone loss or menopausal symptoms.’ In an accompanying Editorial, Drs Grady and Newton expressed their concrete view by saying that ‘despite the efforts of many investigators to find alternatives to estrogen, no therapy, to date, has approached the efficacy of standard-dosage estrogen for treatment of vasomotor symptoms’ [2].

Comment

When a respectable journal publishes a well-performed study which is sponsored by the NIH, one may say that this is the end of the story for soy-isoflavone as therapy for vasomotor symptoms. However, I am afraid this is not the case. The investigators stated, in a preliminary article that described the study protocol [3], that ‘the results of most soy studies in this population have had limitations because of poor design, small sample size, or short duration’. They claimed that their study design avoids the serious methodological limitations that were seen in other trials. The isoflavone tablets provided by the researchers each contained about 50 mg, half of which was daidzein and half genistein. The total daily dose of 200 mg produced isoflavone blood levels slightly above those observed in individuals on an Asian diet but not higher than those observed in infants consuming soy formula. But, despite the convincing results pointing at neutral, or even adverse, effects of soy on vasomotor symptoms, I guess women will still look for safe, over-the-counter natural remedies. Many physicians will continue to recommend such products, based on randomized studies that showed some positive results, such as a recent one by Carmignani and colleagues who concluded that ‘dietary soy supplementation may constitute an effective alternative therapy for somatic and urogenital symptoms of the menopause’ [4]. Ethnicity may be an important key factor for successful therapy. Levis’ cohort was mainly Hispanic-American, Carmignani’s study was done in Brazil, and Aso has reported on good efficacy of S-equol in three randomized studies from Japan [5]. Note that equol, which is a more active metabolite of daidzein, is not produced in the body of the majority of women. Another aspect to be considered is the very high and impressive placebo effect in the context of vasomotor symptoms, which may exceed 50% and help those who campaign for alternative solutions. Thus, my best advice is to remember that every study can provide data and insight that are mainly relevant to its particular clinical and methodological scenarios. Extrapolation of data to other scenarios may be misleading and should be handled carefully.

Comentario

Amos Pines
Department of Medicine T, Ichilov Hospital, Tel-Aviv, Israel

    References

  1. Levis S, Strickman-Stein N, Ganjei-Azar P, et al. Soy isoflavones in the prevention of menopausal bone loss and menopausal symptoms. Arch Intern Med 2011;171:1363-1369.
    http://www.ncbi.nlm.nih.gov/pubmed/21824950

  2. Newton KM, Grady D. Comment on Levis S et al study. Arch Intern Med 2011;171:1369-70.
    http://www.ncbi.nlm.nih.gov/pubmed/21824951

  3. Levis S, Strickman-Stein N, Doerge DR, Krischer J. Design and baseline characteristics of The Soy Phytoestrogens As Replacement Estrogen (SPARE) Study A clinical trial of the effects of soy isoflavones in menopausal women. Contemp Clin Trials 2010;31:293-302.
    http://www.ncbi.nlm.nih.gov/pubmed/20230914

  4. Carmignani LO, Pedro AO, Costa-Paiva LH, Pinto-Neto AM. The effect of dietary soy supplementation compared to estrogen and placebo on menopausal symptoms: a randomized controlled trial. Maturitas 2010;67:262-9.
    http://www.ncbi.nlm.nih.gov/pubmed/20833488

  5. Aso T. Equol improves menopausal symptoms in Japanese women. J Nutr 2010;140:1386-9S.
    http://www.ncbi.nlm.nih.gov/pubmed/20484552