What is it? Overview Usage Side Effects and Warnings

Isoflavones Usage

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Effect of Isoflavones on Menopause

Read more about Menopause and Isoflavones.

Therapeutic Uses

Soy products are known to improve cholesterol profile, but isoflavones may not be the active cholesterol-lowering ingredient in soy. 1 Isoflavones may, however, improve other measures linked to cardiovascular risk, such as levels of blood sugar, insulin, and fibrinogen. 2 According to some but not all studies, soy protein or concentrated isoflavones from soy or red clover may slightly reduce menopausal symptoms , such as hot flashes and vaginal dryness. 3 However, isoflavones have failed to prove effective for the hot flashes that often occur in breast cancer survivors. 4 There is conflicting evidence regarding whether soy or isoflavones may be helpful for preventing osteoporosis , but on balance the evidence suggests a modest beneficial effect. 5 One study tested a purified soy isoflavone product (technically, isoflavone aglycones, as described above ) for treatment of aging skin . 6 In this double-blind trial, 26 Japanese women in their late 30s and early 40s were either given placebo or 40 mg daily of soy isoflavone aglycones for 12 weeks. Researchers monitored two types of wrinkles near the eye: “fine” wrinkles and “linear” wrinkles. The results indicated that use of the soy product significantly reduced “fine” wrinkles as compared to placebo. (Effects on “linear” wrinkles were not significant.) As a secondary measure, researchers also analyzed skin elasticity, and found an improvement in the women given the isoflavones as compared to those given placebo. Note:This was much too small a study for its results to be taken as reliable.

A small and poorly reported double-blind, placebo-controlled study provides weak evidence that red clover isoflavones might be helpful for cyclic mastalgia . 7 A combination product containing soy isoflavones, black cohosh, and dong quai has shown some promise for menstrual migraines . 8 One study found that use of soy isoflavones improved the effectiveness rate of in vitro fertilization (used for female infertility ). 9 A double-blind study performed in China found that use of a soy isoflavone supplement improved blood sugar control in healthy post-menopausal women. 10 In a small double-blind trial, use of soy isoflavones appeared to reduce some symptoms of premenstrual syndrome PMS . 11 A very small study found hints that soy isoflavones might help reduce buildup of abdominal fat. 12

Observational studies hint that soy may help prevent breast and uterine cancer in women. 13 14 15 16 17 18 If this connection is real and not a statistical accident (observational studies are notorious for falling prey to statistical accidents), the explanation may lie in the estrogen-like action of soy isoflavones. As noted above, isoflavones decrease the action of regular estrogen by blocking estrogen receptor sites, and may also reduce levels of circulating estrogen. 19 Since estrogen promotes breast and uterine cancer, these effects could help prevent breast cancer. Soy also appears to lengthen the menstrual cycle by a few days, 20 and this too would be expected to reduce breast cancer risk. However, only a large, long-term intervention trial could actually show that soy or isoflavones reduce breast and uterine cancer risk, and one has not been performed.

Observational studies also hint that soy might help prevent prostate cancer in men. Men have very low levels of circulating estrogen, so the net effect of increased soy consumption might be to increase estrogen-like activity in the body. Since real estrogen is used as a treatment to suppress prostate cancer, perhaps the mild estrogen-like activity of isoflavones has a similar effect. Isoflavones might also decrease testosterone levels and alter ratios of certain forms of estrogen, both of which which would be expected to provide benefit. 21 In one double-blind study, men with early prostate cancer were given either isoflavones or placebo, and their PSA levels were monitored. 22 (PSA is a marker for prostate cancer, with higher values generally showing an increased number of cancer cells.) The results did show that use of isoflavones (60 mg daily) slightly reduces PSA levels. Whether this meant that soy actually slowed the progression of the cancer or simply lowered PSA directly is not clear from this study alone. However, in another study of apparently healthy men (not known to have prostate cancer), soy isoflavones at a dose of 83 mg per day did not alter PSA levels. 23 Taken together, these two studies provide some direct evidence that soy isoflavones may be helpful for treating or preventing prostate cancer, but the case nonetheless remains highly preliminary.

According to most but not all studies, soy isoflavones do notimprove mental function . 24 One study failed to find that soy protein with isoflavones improved general quality of life (health status, depression, and life satisfaction) in post-menopausal women. 25 Soy isoflavones have also failed to prove effective for reducing levels of homocysteine . 26


  1. Yeung J, Yu TF. Effects of isoflavones (soy phyto-estrogens) on serum lipids: a meta-analysis of randomized controlled trials. Nutr J. 2():15.
  2. Crisafulli A, Altavilla D, Marini H, Bitto A, Cucinotta D, Frisina N, Corrado F, D'Anna R, Squadrito G, Adamo EB, Marini R, Romeo A, Cancellieri F, Buemi M, Squadrito F. Effects of the phytoestrogen genistein on cardiovascular risk factors in postmenopausal women. Menopause. 12(2):186-92.
  3. Burke GL, Legault C, Anthony M, Bland DR, Morgan TM, Naughton MJ, Leggett K, Washburn SA, Vitolins MZ. Soy protein and isoflavone effects on vasomotor symptoms in peri- and postmenopausal women: the Soy Estrogen Alternative Study. Menopause. 10(2):147-53.
  4. Van Patten CL, Olivotto IA, Chambers GK, Gelmon KA, Hislop TG, Templeton E, Wattie A, Prior JC. Effect of soy phytoestrogens on hot flashes in postmenopausal women with breast cancer: a randomized, controlled clinical trial. J Clin Oncol. 20(6):1449-55.
  5. 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. 43(4):246-57.
  6. Izumi T, Saito M, Obata A, Arii M, Yamaguchi H, Matsuyama A. Oral intake of soy isoflavone aglycone improves the aged skin of adult women. J Nutr Sci Vitaminol (Tokyo). 53(1):57-62.
  7. Ingram DM, Hickling C, West L, et al. The Breast.
  8. Burke BE, Olson RD, Cusack BJ. Randomized, controlled trial of phytoestrogen in the prophylactic treatment of menstrual migraine. Biomed Pharmacother. 56(6):283-8.
  9. Unfer V, Casini ML, Gerli S, Costabile L, Mignosa M, Di Renzo GC. Phytoestrogens may improve the pregnancy rate in in vitro fertilization-embryo transfer cycles: a prospective, controlled, randomized trial. Fertil Steril. 82(6):1509-13.
  10. Ho SC, Chen YM, Ho SS, Woo JL. Soy isoflavone supplementation and fasting serum glucose and lipid profile among postmenopausal Chinese women: a double-blind, randomized, placebo-controlled trial. Menopause. 14(5):905-12.
  11. Bryant M, Cassidy A, Hill C, Powell J, Talbot D, Dye L. Effect of consumption of soy isoflavones on behavioural, somatic and affective symptoms in women with premenstrual syndrome. Br J Nutr. 93(5):731-9.
  12. Sites CK, Cooper BC, Toth MJ, Gastaldelli A, Arabshahi A, Barnes S. Effect of a daily supplement of soy protein on body composition and insulin secretion in postmenopausal women. Fertil Steril. 88(6):1609-17.
  13. Messina MJ, Persky V, Setchell KD, et al. Soy intake and cancer risk: a review of the in vitro and in vivo data. Nutr Cancer. 1994;21:113-131.
  14. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 29(2):95-120.
  15. Stoll BA. Eating to beat breast cancer: potential role for soy supplements. Ann Oncol. 8(3):223-5.
  16. Day NE. Phyto-estrogens and hormonally dependent cancers. Pathol Biol. 1994;42:1090.
  17. Barnes S, Peterson TG, Coward L. Rationale for the use of genistein-containing soy matrices in chemoprevention trials for breast and prostate cancer. J Cell Biochem Suppl. 22():181-7.
  18. Ingram D, Sanders K, Kolybaba M, Lopez D. Case-control study of phyto-oestrogens and breast cancer. Lancet. 350(9083):990-4.
  19. Nagata C, Kabuto M, Kurisu Y, Shimizu H. Decreased serum estradiol concentration associated with high dietary intake of soy products in premenopausal Japanese women. Nutr Cancer. 29(3):228-33.
  20. Maskarinec G, Franke AA, Williams AE, et al. The effects of an isoflavone intervention on the reproductive cycle of premenopausal women. Presented at: European Conference on Nutrition & Cancer; June 21-24, 2001; Lyon, France.
  21. Goldin BR, Brauner E, Adlercreutz H, Ausman LM, Lichtenstein AH. Hormonal response to diets high in soy or animal protein without and with isoflavones in moderately hypercholesterolemic subjects. Nutr Cancer. 51(1):1-6.
  22. Kumar NB, Cantor A, Allen K, Riccardi D, Besterman-Dahan K, Seigne J, Helal M, Salup R, Pow-Sang J. The specific role of isoflavones in reducing prostate cancer risk. Prostate. 59(2):141-7.
  23. Adams KF, Chen C, Newton KM, et al. Soy isoflavones do not modulate prostate-specific antigen concentrations in older men in a randomized controlled trial. Cancer Epidemiol Biomarkers Prev. 2004;13:644-648.
  24. Messina M, Gardner C, Barnes S. Gaining insight into the health effects of soy but a long way still to go: commentary on the fourth International Symposium on the Role of Soy in Preventing and Treating Chronic Disease. J Nutr. 132(3):547S-551S.
  25. Kok L, Kreijkamp-Kaspers S, Grobbee DE, Lampe JW, van der Schouw YT. A randomized, placebo-controlled trial on the effects of soy protein containing isoflavones on quality of life in postmenopausal women. Menopause. 12(1):56-62.
  26. Reimann M, Dierkes J, Carlsohn A, et al. Consumption of soy isoflavones does not affect plasma total homocysteine or asymmetric dimethylarginine concentrations in healthy postmenopausal women. J Nutr. 2005;136:100-105.


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