Isoflavone Research Initiative

The most recent findings on soy and isoflavones were presented in Washington DC on the occasion of the 9^th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment (October 16-19, 2010). A major part of the topics was dedicated to safety and health benefits in menopausal women, and to the issue of soy and breast cancer.

Prof. em. Takahashi Aso (Tokyo Medical University, Japan) gave details on clinical trials performed in Japanese postmenopausal women exposed to isoflavones (Aso 2010a). Japanese women mostly have a higher exposure to isoflavones through their diet than Western women. In correlation studies the observation of mild as opposed to severe menopausal symptoms was clearly associated with higher urinary levels of equol in 24h urine (and thus with the capability of producing equol), whereas no such association was found for daidzein.

The association between urinary equol levels and reduced menopausal symptoms was put to test in a series of clinical trials (Aso 2010b).

• • In a first randomized trial, 134 Japanese women were assigned to a 12 week supplementation with either placebo (n = 44), 10 mg of S-equol (n = 44), or 30 mg of S-equol per day (n = 46). Habitual isoflavone intake was limited to 20 mg/d. At baseline, total menopausal symptom score varied by menopausal and equol producer status (34.3% producers). After three months, significant differences between premenopausal and perimenopausal/postmenopausal symptom scores were observed for anxiety, somatic, and total scores. The 10 mg-dose was found efficacious, but 30 mg had even more pronounced effects. With 30 mg of S-equol perimenopausal/postmenopausal equol non-producers showed significant decreases from baseline in all menopausal symptom scores except depression (p < 0.01) (Ishiwata et al. 2009).
• • In a second trial 126 Japanese women were supplemented for 12 weeks with placebo (n = 60) or 10 mg of S-equol (n = 66). The double-blind design excluded placebo-responders through a run-in phase. At the end of the study the frequency of hot flushes was reduced by 34.5 % in the placebo group, and by 54 % in the isoflavone group (Aso 2010b).
• • The third trial was an 8 week dose-finding study performed in 100 US-American post-menopausal women. Study participants were allocated to 10, 20 or 40 mg of S-equol daily, or to 50 mg of isoflavones. The 10 mg dose of equol gave results in the same order of magnitude as 50 mg of the isoflavone mixture. Better effects were found in women experiencing more than 8 hot flushes daily. The effect was dose-dependent: with 10, 20 and 40 mg S-equol and with 50 mg of complex isoflavones a 50 % reduction of hot flushes was reached in 25.0, 27.3, 42.9 and 20.0 % of women after 8 weeks of supplementation (Aso 2010b).

No safety issues became apparent during the studies. The supplementation had no effect on hormonal levels and on parameters of the thyroid gland (TSH, T3, T4). Endometrial thickness and vaginal cytology remained unaltered.

References

Aso T (2010a). Efficacy and safety of a natural S-equol supplement for menopausal healthcare. 9^th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment, Washington DC, 16-19 October.

Aso T (2010b). Equol improves menopausal symptoms in Japanese women. J Nutr 140(7):1386S-1389S.

Ishiwata N, Melby MK, Mizuno S and Watanabe S (2009). New equol supplement for relieving menopausal symptoms: randomized, placebo-controlled trial of Japanese women. Menopause 16(1):141-148.