Genistein is an isoflavone extracted from soybeans. Its structural resemblance to sex hormones such as estradiol enables it to alter the body’s reponse to these hormones. Genistein’s broad range of medical applications probably stem from its ability to inhibit various enzymes that have wide-ranging actions in many tissues. The half-life of genistein supplements in the body is about 8 hours.
Clinical trials, animal studies, cell-culture experiments, and epidemiological studies have provided evidence for the following physiological effects of genistein:
- reducing symptoms of allergic asthma
- strengthening bone due to estrogen deficiency, especially in the spine
- protection of nerve cells from damage caused by hormone shortages and Alzheimer’s proteins
- breast enlargement
- inhibition of growth and spread of various cancers — including cancer of the ovaries, colon, prostate, thyroid, skin, and head and neck; non-Hodgkin lymphoma, malignant melanoma, certain leukemias and lung cancers, and possibly breast cancer
- counteracting the effects of the DeltaF508 mutation that causes cystic fibrosis
- lowering body fat
- improving insulin responses to blood sugar
- lowering total cholesterol and LDL levels, increasing HDL levels
- decreasing symptoms of Raynaud’s Disease
- inhibiting growth of atherosclerotic plaques in blood vessels
- increasing arterial elasticity, lowering high blood pressure
- preventing aging effects of UV light on skin
- enhancing the bioavailability of many hard-to-absorb substances
Some of these effects of genistein are still controversial, since they were seen in some studies and not in others. Such discrepancies often are the result of inadequate dosing.
Bone strengthening effects were seen using various isoflavone regimens — one such study used 44 mg/day of isoflavones including 1 mg genistein and 0.5 mg daidzein; another study used 54 mg/day of pure genistein. Beneficial effects on cholesterol were seen when 42 mg/day of genistein was used. Other isoflavones, such as daidzein and glycitein, share many of genistein’s actions in the body.
One study suggests that the supplement I3C (indole-3-carbinol) works synergistically with genistein to suppress estrogen-related cancers.