After their estrogenic properties were found, plant-derived isoflavones have been gaining rising popularity in treating ailments connected with menopause. Approximately 20% of women going through menopause transition seek doctor’s help to alleviate the unpleasant symptoms (1). As hormone replacement therapy involves certain risks, there is a significant need for a safe alternative. An increasing frequency of women choosing soy products is attributed to their belief that soy-derived supplements are natural, mild and efficient. Yet most studies cannot confirm the beneficial effects of soya. Soy Phytoestrogens as Replacement Estrogens (SPARE) trial was published recently in Archives of Internal Medicine (2). It suggests that phytoestrogens work as poorly as placebo. Did we get our hopes too high?
Genistein and daidzein are the two soya beans isoflavones, which are considered to have unique properties. Apart from their antioxidant effects, both phytoestrogens seem to bind to estrogen receptors, react with enzymes engaged in hormone production, or even interact with sex hormone binding globulines (SHBG). However, their outcomes make up only 0,001 strength of natural 17-ß-estradiol. Research into the possible beneficial actions of phytoestrogens has led to surprising conclusions. These isoflavones present estrogenic as well as antiestrogenic features in a dose-dependent way. Soy products do not change male fertility in any way (3). Therefore their impact on human organism seems to be diversified.
The hypothesis of xenoestrogens’ advantageous qualities originates from one discovery. Namely, it was found that Asian women, whose diet is known to be rich in soya beans, suffer from breast cancer and cardiovascular disease less frequently than Western females. Moreover, in this region the prevalence of osteoporotic fractures is lower (4). These characteristics are thought to be attributed to Asian soy-rich diet, which provides about 50-100mg isoflavones a day.
Menopause. Cell degeneration. Vaginitis.
For the past few years there have been contradictory reports on potentially beneficial effects of genistein and daidzein on alleviating symptoms connected with menopause transition. An appropriate medication for menopausal women would, like classic hormone replacement therapy, prevent the rapid bone density loss which takes place in the first years after the last period. Cochrane review (5) prepared in 2007 revealed no evidence that phytoestrogens work with no indication of their harmfulness. Some meta-analyses, such as the Clinical Nutrition publication from 2008 (6), suggested that soy-products did increase bone mineral density in menopausal women. But the researchers admit that many trials included in the analyses were limited by poor design, short duration and small number of participants.
SPARE study was designed to overcome these flaws. This prospective, randomized, double-blind trial embraced about 250 women aged 45 to 60 years within 5 years of menopause. Their bone mineral density T score was −2.0 or higher in the lumbar spine. Patients were randomly assigned to receive daily soy isoflavone tablets at a dosage of 200 mg, the highest in history of soy-derived isoflavons research, or placebo. Subjects were followed up after 2 years. Results showed no significant differences between the participants assigned to soy tablets (n=122) and those taking placebo (n=126) regarding changes in bone mineral density in the spine (−2.0% and −2.3%, respectively), the total hip (−1.2% and −1.4%), or the femoral neck (−2.2% and −2.1%). Actually, larger proportion of participants in the soy group went through hot flashes. Constipation was also more common compared to the control group.
Scientists are trying to understand the existence of an alarmingly large number of conflicting studies. In fact, the results of taking soy isoflavones may differ between individuals. It has been suggested that women who have intestinal bacteria producing equol, which is an active metabolite of daidzein (25-50% of the population (7)) are more likely to benefit from soy food intake. Factors such as ethnicity, body weight and smoking also have an influence on the rate of menopausal bone loss. Still, it seems that no therapy other than an estrogen one offers a confident relief in menopausal symptoms and prevention of osteoporosis. It appears that both clinicians and patients need to take a critical look at soy phytoestrogens as they, apart from being natural and “friendly”, offer rather a waste of money than the real effect.
1.Soy Isoflavones for Prevention of Menopausal Bone Loss and Vasomotor Symptoms. Comment on “Soy Isoflavones in the Prevention of Menopausal Bone Loss and Menopausal Symptoms”. Katherine M. Newton, PhD; Deborah Grady, MD, MPH. Arch Intern Med. 2011;171(15):1369-1370.
2.Levis S, et al. Soy isoflavones in the prevention of menopausal bone loss and menopausal symptoms. Arch Intern Med 2011; 171(15): 1363-1369.
3.Hamilton-Reeves JM, Vazquez G, Duval SJ, Phipps WR, Kurzer MS, Messina MJ (2010). “Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis”. Fertil Steril. 94 (3): 997–1007. doi:10.1016/j.fertnstert.2009.04.038. PMID 19524224.
4.Messina M. Investigating the optimal soy protein and isoflavone intakes for women: a perspective. Womens Health (Lond Engl). 2008;4(4):337-356.
5.Lethaby AE, Brown J, Marjoribanks J, Kronenberg F, Roberts H, Eden J (2007). Lethaby, Anne. ed. “Phytoestrogens for vasomotor menopausal symptoms”. Cochrane Database Syst Rev (4): CD001395. doi:10.1002/14651858.CD001395.pub3.PMID 17943751.
6.Ma D-F, Qin L-Q, Wang P-Y, Katoh R. Soy isoflavone intake increases bone mineral density in the spine of menopausal women: meta-analysis of randomized controlled trials. Clin Nutr. 2008;27(1):57-64.
7. Lampe JW. Is equol the key to the efficacy of soy foods? Am J Clin Nutr. 2009;89:16645-16675.