Introduction

Scientists classify soy isoflavones from the plant Glycine max as phytoestrogens. Phyto is a Greek root word meaning plant, so phytoestrogens are plant-based compounds that have estrogen-like activity. Because they are structurally similar to estrogens, isoflavones exert weak estrogenic activity. Because of their estrogen-like effects, isoflavones have been studied for a wide spectrum of health benefits.

Soybeans and soy foods like tofu are the best dietary source of isoflavones. However, many soy protein concentrates and soy products processed with alcohol may not contain isoflavones. A synthetically derived form of isoflavones, known as ipriflavone, is also available.

Dosage Info

Dosage Range

10-300mg daily.

Most Common Dosage

60mg daily.

Dosage Forms

Powders, granules, tablets, capsules, and liquids.

Interactions and Depletions

Interactions

• Estrogen and estrogen-like medications
• tamoxifen

Reported Uses

Because soy isoflavones exert mild effects like that of estrogen, they may be useful for treating symptoms associated with menopause. (1) , (2) , (3) A long-term study indicated that soy phytoestrogens when given to postmenopausal women resulted in an increase occurrence of endometrial hyperplasia. (4) The phytoestrogens in isoflavones may inhibit cancer-inducing estrogens. Because high estrogen levels are a risk factor for breast cancer, isoflavones may play a role in reducing this risk. (5) , (6) Other studies have indicated that isoflavones may actually stimulate the growth of estrogen-dependent breast cancer cells. (7) It has also been reported that high consumption of soy isoflavones may reduce the incidence of prostate cancer in men. (8)

Also of potential benefit to women, isoflavones may support bone health (9) and reduce the effects of osteoporosis. (10) , (11) This benefit is being challenged. A well-designed study evaluated the use of ipriflavone, a synthetic isoflavone, in more than 470 postmenopausal women with osteoporosis. Ipriflavone did not prevent bone loss when compared to placebo. (12)

Isoflavones may also support cardiovascular health through a variety of mechanisms. It may help lower cholesterol. (13) , (14) , (15) , (16) A study involving postmenopausal women found that soy isoflavones exerted favorable effects on vasomotor symptoms and a reduction in LDL and an increase in HDL levels. (17) Soy milk may help lower blood pressure. After 3 months the individuals consuming soy milk had a modest, but greater, decrease in blood pressure compared to those consuming cow’s milk. (18) These benefits could potentially reduce the risk of atherosclerosis and other cardiovascular diseases. (19) ,, (20)

Toxicities & Precautions

Introduction

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General

This dietary supplement is considered safe when used in accordance with proper dosing guidelines.

Health Conditions

If you are on kidney dialysis, talk to your doctor before taking this dietary supplement. (21)

Scientific studies have reported that certain ingredients contained in this dietary supplement act similar to the body’s natural hormone estrogen. If you have or are susceptible to hormonally related cancers, such as breast, ovarian and prostate, talk to your doctor before taking this dietary supplement.

Consuming large amounts of soy isoflavones could suppress thyroid function and/or cause a worsening of hypothyroidism. (22) If you have any type of thyroid disease talk to your doctor before taking this dietary supplement.

Side Effects

Side effects are possible with any dietary supplement. Ipriflavone, a synthetic isoflavone, may cause a decrease in the number of lymphocytes found in the blood. Talk to your doctor before taking ipriflavone so that proper monitoring, if necessary, can be assured. (23)

Pregnancy / Breast Feeding

To date, the medical literature has not reported any adverse effects related to fetal development during pregnancy or to infants who are breast-fed. Yet little is known about the use of this dietary supplement while pregnant or breast-feeding. Therefore, it is recommended that you inform your healthcare practitioner of any dietary supplements you are using while pregnant or breast-feeding.

Age Limitations

There is some concern about the use of soy-based infant formulas. Some researchers suggest that exposing infants to high levels of soy isoflavones can cause problems with the infant’s hormonal development. (24) Otherwise, the medical literature has not reported any adverse effects specifically related to the use of this dietary supplement in children. Since young children may have undiagnosed allergies or medical conditions, this dietary supplement should not be used in children under 10 years of age unless recommended by a physician.

References

1. View Abstract: Murkies AL, Lombard C, Strauss BJ, et al. Dietary Flour Supplementation Decreases Post-Menopausal Hot Flushes: Effect of Soy and Wheat. Maturitas. 1995;21:189.
2. View Abstract: Albert A, et al. Efficacy and safety of a phytoestrogen preparation derived from Glycine max (L.) Merr in climacteric symptomatology: a multicentric, open, prospective and non-randomized trial. Phytomedicine. Mar2002;9(2):85-92.
3. View Abstract: Arena S, et al. A natural alternative to menopausal hormone replacement therapy. Phytoestrogens. Minerva Ginecol. Feb2002;54(1):53-7.
4. View Abstract: Unfer V, Casini ML, Costabile L, Mignosa M, Gerli S, Di Renzo GC. Endometrial effects of long-term treatment with phytoestrogens: a randomized, double-blind, placebo-controlled study. Fertil Steril. Jul2004;82(1):145-8.
5. View Abstract: Tham DM, et al. Clinical Review 97: Potential Health Benefits of Dietary Phytoestrogens: A Review of the Clinical, Epidemiological, and Mechanistic Evidence. J Clin Endocrinol Metab. Jul1998;83(7):2223-35.
6. View Abstract: Xu X, Harris KS, Wang HJ, Murphy PA. Bioavailability of Soybean Isoflavones Depends upon Gut Microflora in Women. J Nutr. 1995;125:2307.
7. View Abstract: Allred CD, Allred KF, Ju YH, et al. Soy diets containing varying amounts of genistein stimulate growth of estrogen-dependent (MCF-7) tumors in a dose-dependent manner. Cancer Res. Jul2001;61(13):5045-50.
8. View Abstract: Jacobsen BK, Knutsen SF, Fraser GE. Does high soy milk intake reduce prostate cancer incidence? The Adventist Health Study (United States). Cancer Causes Control. Dec1998;9(6):553-7.
9. View Abstract: Chen YM, Ho SC, Lam SS, Ho SS, Woo JL. Beneficial effect of soy isoflavones on bone mineral content was modified by years since menopause, body weight, and calcium intake: a double-blind, randomized, controlled trial. Menopause. May2004;11(3):246-54.
10. View Abstract: Potter SM, Baum JA, Teng H, et al. Soy Protein and Isoflavones: Their Effect on Blood Lipids and Bone Density in Postmenopausal Women. Am J Clin Nutr. Dec1998;68(Suppl6):1375S-79S.
11. View Abstract: Lydeking-Olsen E, Beck-Jensen JE, Setchell KD, Holm-Jensen T. Soymilk or progesterone for prevention of bone loss. A 2 year randomized, placebo-controlled trial. Eur J Nutr. Aug2004;43(4):246-57.
12. View Abstract: Alexandersen P, Toussaint A, Christiansen C, et al. Ipriflavone in the Treatment of Postmenopausal Osteoporosis, A Randomized Controlled Trial. JAMA. 2001;285:1482-1488.
13. View Abstract: Goodman-Gruen D, Kritz-Silverstein D. Usual dietary isoflavone intake is associated with cardiovascular disease risk factors in postmenopausal women. J Nutr. Apr2001;131(4):1202-6.
14. View Abstract: Scheiber MD, Liu JH, Subbiah MT, et al. Dietary inclusion of whole soy foods results in significant reductions in clinical risk factors for osteoporosis and cardiovascular disease in normal postmenopausal women. Menopause. Sep2001;8(5):384-92.
15. View Abstract: Sagara M, Kanda T, NJelekera M, et al. Effect of Dietary Intake of Soy Protein and Isoflavones on Cardiovascular Disease Risk Factors in High Risk Middle-Aged Men in Scotland. J Am Coll Nutr. Feb2004;23(1):85-91.
16. View Abstract: Zhuo XG, Melby MK, Watanabe S. Soy Isoflavone Intake Lowers Serum LDL Cholesterol: A Meta-Analysis of 8 Randomized Controlled Trials in Humans. J Nutr. Sep2004;134(9):2395-400.
17. View Abstract: Petri Nahas E, Nahas Neto J, De Luca L, Traiman P, Pontes A, Dalben I. Benefits of soy germ isoflavones in postmenopausal women with contraindication for conventional hormone replacement therapy. Maturitas. Aug2004;48(4):372-80.
18. View Abstract: Rivas M, Garay RP, Escanero JF, Cia P Jr, Cia P, Alda JO. Soy milk lowers blood pressure in men and women with mild to moderate essential hypertension. J Nutr. Jul2002;132(7):1900-2.
19. View Abstract: Anthony MS, Clarkson TB, Williams JK. Effects of Soy Isoflavones on Atherosclerosis: Potential Mechanisms. Am J Clin Nutr. Dec1998;68(Suppl6):1390S-93S.
20. View Abstract: Goodman-Gruen D, Kritz-Silverstein D. Usual dietary isoflavone intake is associated with cardiovascular disease risk factors in postmenopausal women. J Nutr. Apr2001;131(4):1202-6.
21. View Abstract: Fanti P, et al. Serum levels and metabolic clearance of the isoflavones genistein and daidzein in hemodialysis patients. J Am Soc Nephrol. Apr1999;10(4):864-71.
22. View Abstract: Divi RL, Chang HC, Doerge DR. Anti-thyroid isoflavones from soybean: isolation, characterization, and mechanisms of action. Biochem Pharmacol. Nov1997;54(10):1087-96.
23. View Abstract: Alexandersen P, Toussaint A, Christiansen C, et al. Ipriflavone in the Treatment of Postmenopausal Osteoporosis, A Randomized Controlled Trial. JAMA. 2001;285:1482-1488.
24. View Abstract: Setchell KD, Zimmer-Nechemias L, Cai J, Heubi JE. Exposure of infants to phyto-oestrogens from soy-based infant formula. Lancet. Jul1997;350(9070):23-7.