Isoflavones Usage

Read more about Menopause and Isoflavones.

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