Soy & Menopausal Health

Menopause is the permanent ending of menstruation that coincides with a marked decline in estrogen levels.¹ For many women, the decline in estrogen triggers the onset of hot flashes, and when women move beyond menopause into postmenopause, they are at increased risk of developing coronary heart disease (CHD) and osteoporosis.

The extent to which the decrease in estrogen production, as opposed to the aging process itself, is responsible for the increased risk of CHD is a matter of some debate.^{2, 3} There is no dispute however that the decline in estrogen levels causes substantial bone loss in many women.⁴

Many women object to the medicalization of menopause,⁵ and recent clinical trial data show that the harmful effects of conventional hormone therapy can outweigh the benefits for some women. Soy is among the alternatives suggested for relieving menopausal symptoms.^6,7

Soy foods are a rich, and essentially unique, dietary source of isoflavones,⁸ also referred to as phytoestrogens because they have a similar chemical structure to the hormone estrogen. Soy isoflavones bind to estrogen receptors, and exert some estrogen-like effects under certain experimental conditions. Although isoflavones do share some common properties with estrogen, they are also quite different in many ways.

There is evidence suggesting that soy foods may be particularly beneficial to postmenopausal women by helping to alleviate hot flashes, and by reducing the risk of coronary heart disease and osteoporosis.

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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 10-15 percent of women with hot flashes, they are frequent and severe.⁹ Hot flashes are often treated with hormone therapy, but soy is gaining recognition as a treatment alternative.

More than 25 clinical trials regarding soy and hot flashes have been conducted^10-13 and results have been inconsistent, not surprising due to considerable variation in the way individuals metabolize isoflavones.¹⁴

However, according to one recent analysis, the clinical data recommends that women with frequent (≥ 5/day) hot flashes try soy foods for relief of menopausal symptoms, even though it did not definitively conclude that soy foods are efficacious.¹⁵ In studies showing a reduction in hot flashes, improvements are generally seen within three to four weeks.

Japanese women have a significantly lower rate of hot flashes, which may be contributed to a diet rich in soy beans.

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References

1. Greendale GA, Lee NP, Arriola ER. The menopause. Lancet 1999;353:571-580.
2. Lawlor DA, Ebrahim S, Davey Smith G. Role of endogenous oestrogen in aetiology of coronary heart disease: analysis of age related trends in coronary heart disease and breast cancer in England and Wales and Japan. BMJ 2002;325:311-312.
3. Barrett-Connor E. Sex differences in coronary heart disease. Why are women so superior? The 1995 Ancel Keys Lecture. Circulation 1997;95:252-264.
4. Heaney RP. The skeletal response to estrogen. Metabolism 2000;49:1083-1084.
5. Singh A, Kaur S, Walia I. A historical perspective on menopause and menopausal age. Bull Indian Inst Hist Med Hyderabad 2002;32:121-135.
6. Writing Group for the Women's Health Initiative Investigators. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results From the Women's Health Initiative randomized controlled trial. JAMA 2002;288:321-333.
7. Minelli C, Abrams KR, Sutton AJ, Cooper NJ. Benefits and harms associated with hormone replacement therapy: clinical decision analysis. BMJ 2004;328:371.
8. Franke AA, Custer LJ, Wang W, Shi CY. HPLC analysis of isoflavonoids and other phenolic agents from foods and from human fluids. Proc Soc Exp Biol Med 1998;217:263-273.
9. Kronenberg F. Hot flashes: epidemiology and physiology. Ann N Y Acad Sci 1990;592:52-86; discussion 123-133.
10. Krebs EE, Ensrud KE, MacDonald R, Wilt TJ. Phytoestrogens for treatment of menopausal symptoms: a systematic review. Obstet Gynecol 2004;104:824-836.
11. Balk E, Chung M, Chew P, Ip S, Raman G, Kuplenick B, Tatsioni A, Sun Y, Wolk B, DeVine D, Lua J. Effects of soy on health outcomes. Evidence report/technology assessment No. 126 (prepared by Tufts-New England Medical Center Evidence-based Practice Center under Contract No. 290-02-0022.) AHRQ Publication No. 05-E024-2. Rockville, MD Agency for Healthcare Research and Quality; July 2005.
12. Huntley AL, Ernst E. Soy for the treatment of perimenopausal symptoms--a systematic review. Maturitas 2004;47:1-9.
13. Nelson HD, Haney E, Humphrey L, Miller J, Nedrow A, Necolaidis C, Vesco K, Walker M, Bougatsos C, Nygren P. Management of menopause-related symptoms. Summary, Evidence Report/Technology Assessment No. 120. (prepared by the Oregon Evidence-based Practice Center, under contract No. 290-02-0024.) AHRQ Pub. No. 05-E016-1. Rockville, MD: Agency for Health Research Quality; 2005 March.
14. Rowland I, Faughnan M, Hoey L, Wahala K, Williamson G, Cassidy A. Bioavailability of phyto-oestrogens. Br J Nutr 2003;89 Suppl 1:S45-58.
15. Messina M, Hughes C. Efficacy of soy foods and soy bean isoflavone supplements for alleviating menopausal symptoms is positively related to initial hot flush frequency. J Med Food 2003;6:1-11.
16. American Heart Association. Heart Disease and Stroke Statistics -- 2005 Update. Dallas, Texas: American Heart Association; 2005.