Soy & Menopausal Symptom Relief

Introduction

Menopause refers to the permanent ending of menstruation¹ – a natural part of a woman's life cycle. As a result of the marked decline in estrogen levels that occurs at this time many women, as much as two-thirds of the menopausal population in Western countries, report having hot flashes.^2,3 The decline in estrogen levels also leads to a loss in bone density as bone breakdown exceeds bone formation.⁴ Consequently, risk of developing osteoporosis and having a fracture increases.⁵ Although heart disease risk increases with age, the extent to which the lower estrogen levels contribute to this increase is a matter of debate.^6,7

For multiple reasons, many women object to the medicalization of menopause⁸ and would prefer to avoid conventional medical treatments for menopause symptoms. Interest in identifying alternatives to medication increased markedly after the Women's Health Initiative Trial showed that the harmful effects of conventional hormone therapy – long the first choice for menopause symptom relief – outweighed the benefits.^9,10 One of the most popular alternatives is soy, which is of interest to the medical community because it contains a group of compounds called isoflavones.

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Isoflavones

Soyfoods are a rich, and essentially unique, dietary source of isoflavones.¹¹ Isoflavones are often referred to as phytoestrogens because they have a similar chemical structure to the hormone estrogen and exert estrogen-like effects under certain conditions. However, although isoflavones do share some common properties with estrogen, they are also different in many ways. In fact, in some tissues isoflavones have no effects, whereas estrogen does and in others, isoflavones have effects opposite to those of estrogen.¹²

It is well recognized that Japanese women report having fewer hot flashes than European and North American women.¹³ Furthermore, some studies show that among Japanese women, those who consume the most soy have fewer hot flashes.¹⁴ There is also clinical evidence indicating that isoflavone supplements may offer an effective treatment for hot flashes.

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Hot Flashes

For many women, hot flashes are a classic sign of menopause, and the most common reason for seeking treatment. A hot flash produces a sudden sensation of warmth or even intense heat that spreads over various parts of the body, especially the chest, face and head. In about 10 to 15 percent of women with hot flashes, the symptoms are frequent and severe.¹⁵

More than 50 hot flash trials evaluating the efficacy of isoflavone-containing products have been conducted. To simplify the experimental design, many of the more recently conducted trials have used soy extracts (isoflavone supplements) rather than soyfoods. Generally, most trials used the amount of isoflavones found in about two servings of soyfoods. Over the past few years, several reviews and analyses of the study results have been published, but with mixed conclusions.^16,17 Several explanations for the mixed data have been proposed.^18,19

In an attempt to provide some clarity about the effects of isoflavones on the alleviation of hot flashes, a team of investigators including those from the National Institutes of Health in Japan and the University of Minnesota conducted a comprehensive analysis of the literature, although only studies evaluating the effects of isoflavone supplements – not whole soyfoods – were considered. Isoflavone supplements were found to reduce the frequency and severity of hot flashes by approximately 50 percent. For women suffering from hot flashes, this degree of relief represents a significant improvement in the quality of life.

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Summary and Conclusion

For many women hot flashes can greatly impact quality of life. Although the hormone estrogen is known to alleviate hot flashes, for many reasons a large portion of menopausal women prefer to seek relief with a more natural, non-pharmaceutical approach. Clinical evidence suggests that soyfoods may offer one such approach.

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References

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2. Thurston RC, Sowers MR, Chang Y, Sternfeld B, Gold EB, Johnston JM, et al. Adiposity and reporting of vasomotor symptoms among midlife women: the study of women's health across the nation. Am J Epidemiol 2008;167:78-85.
3. Gold EB, Colvin A, Avis N, Bromberger J, Greendale GA, Powell L, et al. Longitudinal analysis of the association between vasomotor symptoms and race/ethnicity across the menopausal transition: study of women's health across the nation. Am J Public Health 2006;96:1226-35.
4. Masse PG, Dosy J, Jougleux JL, Caissie M, Howell DS. Bone mineral density and metabolism at an early stage of menopause when estrogen and calcium supplement are not used and without the interference of major confounding variables. J Am Coll Nutr 2005;24:354-60.
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15. Kronenberg F. Hot flashes: epidemiology and physiology. Ann N Y Acad Sci 1990;592:52-86; discussion 123-33.
16. Howes LG, Howes JB, Knight DC. Isoflavone therapy for menopausal flushes: a systematic review and meta-analysis. Maturitas 2006;55:203-11.
17. Lethaby A, Brown J, Marjoribanks J, Kronenberg F, Roberts H, Eden J. Phytoestrogens for vasomotor menopausal symptoms. Cochrane Database Syst Rev 2007:CD001395.
18. Messina M, Hughes C. Efficacy of soyfoods and soybean isoflavone supplements for alleviating menopausal symptoms is positively related to initial hot flush frequency. J Med Food 2003;6:1-11.
19. Williamson-Hughes PS, Flickinger BD, Messina MJ, Empie MW. Isoflavone supplements containing predominantly genistein reduce hot flash symptoms: a critical review of published studies. Menopause 2006;13:831-9.