The authors of this study were testing the hypothesis that Asian women may have fewer health complaints and that this may be due to higher consumption of soy products. This double-blind, placebo-controlled randomized study assessed the effect of soy isoflavones on menopausal symptoms, bone mineral density (BMD), serum cytokines, and bone metabolism indices.
Chinese menopausal women were recruited from 3 medical centers in China. Women were between the ages of 45 and 55, had moderate menopause symptoms based on a questionnaire and were excluded if they had menopausal symptoms for more than 5 years, high blood pressure, endocrine disorders, cardiovascular disease, or were currently on hormone replacement therapy (HRT), pregnant, obese, or allergic to soy products.
Women were given capsules of soy isoflavone (22.5 mg, 52.2% genistein, 47.8% daidzein) or placebo, 2 capsules twice a day for 6 months. They were asked to limit their soy dietary consumption. A menopause symptom questionnaire and BMD of the radius and tibia (using ultrasound measurement) were done at baseline and at 6 months. Blood tests included genistein, daidzein, calcium, phosphorus, alkaline phosphatase (ALP), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α).
A total of 70 women completed the study (37 in treatment group and 33 in placebo group). There were overall significant decreases in menopausal symptoms such as hot flashes, insomnia, restlessness and tantrums, dizziness, lassitude, headache, heart palpitations, feeling of crawling skin, urinary tract infection, and state of sexual life of 11.5 points in the treatment group vs. 7.3 points in the placebo group. And, for almost all of the same symptoms in the placebo group (all P<0.05). Hot flashes specifically, significantly decreased in the isoflavone group vs. no significant decrease in the placebo group.
The BMD of the tibia increased significantly with soy isoflavone ingestion, although the radial BMD did not change. Alkaline phosphatase, IL-6, and TNF-α decreased significantly in the treatment group as well.
Commentary: Common perimenopause and postmenopausal symptoms include hot flashes, insomnia, and night sweats. There is also a normal bone loss, especially in the first 4 years, associated with the decline of estrogen, which can increase the risk of osteoporosis and fractures. Soy isoflavones have been shown to decrease bone loss in animal and human studies, likely due to the phytoestrogens that have weak estrogenic activity. Not all published reports confirm that Asian women have less menopause symptoms than Western Caucasian women, but if they do in fact, it is hypothesized that one reason may be the higher consumption of soy products in Asia.
To summarize, in this study, soy isoflavones had a significant, positive effect on a number of subjective and objective markers of menopause including the decrease in overall symptoms of menopause and an increase in the tibia BMD. Alkaline phosphatase levels and TNF-alpha normally rise after menopause and IL-6 is partially regulated by estrogen. Because soy isoflavones possess weak estrogen-like properties, they may alter bone formation and resorption in a manner similar to estrogen. Soy isoflavones appear to decrease blood levels of ALP, IL-6, and TNF-α, suggesting again their weak estrogenic effect and favorable influence on bone metabolism. This study should not be construed as concluding that soy isoflavones have equivalent effects of estrogen therapy, on either menopause symptoms or on slowing bone loss, but this simple intervention does have endocrine effects that have clinical meaning in menopause management.
Chi X-X, Zhang T. The effects of soy isoflavone on bone density in north region of climacteric Chinese women. J Clin Biochem Nutr. September 2013;53(2):102-107