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.

Dr. Mindy Kurzer (University of Minnesota, Minnesota, USA) performed a meta-analysis of the studies with isoflavone-containing preparations on the improvement of menopausal symptoms (Taku et al. 2010). Approximately 50 clinical trials have evaluated the effects of isoflavones of soy foods on postmenopausal hot flushes. To date, three meta-analyses on soy have been published, all three with positive results in favour of isoflavones:

• - Nelson examined exclusively hot flush frequency in six trials with soy extracts, and found a reduction in frequency by 1-1.5 hot flushes per day (Nelson et al. 2006).
• - Howes examined 12 trials including extracts, food and soy protein, and found a decrease of frequency and severity by 34 % (Howes et al. 2006).
• - A recent meta-analysis made by Bolanos examined 9 trials with a duration of 12 weeks, and found a 40 % reduction of hot flushes frequency per day (Bolanos et al. 2010).

The new meta-analysis of Kurzer used different inclusion criteria: e.g., in cross-over studies only the first study period was evaluated in order to avoid problems with carry-over effects. Kurzer et al. excluded trials with other isoflavone sources than soy, and also excluded comparisons with estrogen replacement therapy. Of 41 eligible trials, 23 had to be excluded, which resulted in 17 randomized controlled trials published in 18 papers. 12 of these studies made indications on hot flush frequency, 8 on severity. Most trials were conducted for 12 weeks and used doses of 40-100 mg of isoflavones per day.

All 12 trials giving details on hot flush frequency showed reductions, which in 75 % of cases reached statistical significance. Of 9 trials examining hot flush severity, 44 % indicated a significant benefit. A meta-analysis of the 12 studies that evaluated hot flush frequency showed that isoflavone consumption significantly reduced hot flush frequency by 15.6 % over placebo (p < 0.0001). An analysis of the 8 trials that evaluated hot flush severity demonstrated that isoflavone consumption also significantly reduced hot flush severity by 24.5 % over placebo (p < 0.0007).

Longer treatment duration has a positive effect on the study outcome. Most importantly, the effect did not diminish over time. The results of the analysis show conclusively that consumption of soy isoflavones significantly reduces frequency and severity of hot flushes by about 20 % more than placebo. The actual benefit experienced by the women includes the placebo effect and is therefore in the range of a 50 % overall improvement. Such an effect represents a significant improvement in the quality of life for women suffering from hot flushes.

References

Bolanos R, Del Castillo A and Francia J (2010). Soy isoflavones versus placebo in the treatment of climacteric vasomotor symptoms: systematic review and meta-analysis. Menopause 17(3):660-666.

Howes LG, Howes JB and Knight DC (2006). Isoflavone therapy for menopausal flushes: a systematic review and meta-analysis. Maturitas 55(3):203-211.

Nelson HD, Vesco KK, Haney E, Fu R, Nedrow A, Miller J, Nicolaidis C, Walker M and Humphrey L (2006). Nonhormonal therapies for menopausal hot flashes: systematic review and meta-analysis. JAMA 295(17):2057-2071.

Taku K, Melby MK, Messina M, Kronenberg F and Kurzer M (2010). Soy isoflavones reduce postmenopausal hot flash frequency and severity: Results of a systematic review and meta-analysis of randomized controlled trials. 9^th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment, Washington DC, 16-19 October.