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Genistein

Proposed Uses: Cancer prevention; Osteoporosis prevention; Amyotrophic Lateral Sclerosis; High Cholesterol; Menopausal Symptoms; Osteoporosis

Genistein is a type of chemical called a phytoestrogen—an estrogen-like substance present in some plants. There are two main types of phytoestrogens: isoflavones and lignans. Soy is the most abundant source of isoflavones, with genistein the most abundant isoflavone in soy. Red clover is also a good course of genistein.

Like other phytoestrogens, genistein can work in two ways: either by increasing or decreasing the effects of estrogen. This happens because genistein binds to special sites on cells called estrogen receptors. Genistein stimulates these receptors, but not as strongly as real estrogen; at the same time, it blocks estrogen itself from attaching. The net result is that when there is a lot of estrogen in the body, such as before menopause, genistein may partly block its effects.

Since estrogen appears to increase the risk of various forms of cancer, regular use of genistein by premenopausal women might help reduce this risk. On the other hand, if there is little human estrogen present, such as after menopause, genistein can partly make up for it. This is one rationale for using genistein to prevent osteoporosis.

Genistein might also be helpful for reducing heart disease risk.

Requirements/Sources
Genistein is found in high quantities in soy and in negligible quantities in a few other foods. Most soy foods contain about 1 to 2 mg of genistein per gram of protein.

Therapeutic Dosages
The optimum dosage of genistein is unknown. In Asia, population groups who eat soy foods daily containing 20 to 80 mg of genistein have lower rates of breast and prostate cancer than do groups in the West with less genistein in their diets.  However, we don't know whether genistein are responsible for this effect.

Therapeutic Uses
Studies have found that genistein may be helpful for preventing heart disease and preventing or treating osteoporosis.  Weaker evidence suggests potential benefits in cancer prevention, cancer treatment, and amyotrophic lateral sclerosis (ALS)

Safety Issues
Most safety studies that have implications for genistein involved mixed isoflavones from soy or red clover. For more information, see the Safety Issues section of the isoflavone article.

Additionally, some evidence suggests that the genistein in particular might impair immunity. One study in mice found that injected genistein has negative effects on the thymus gland (an organ that is important for immunity) and also causes changes in the prevalence of various white blood cells consistent with impaired immunity.  Although the genistein was injected rather than administered orally, the blood levels of genistein that these injections produced were not excessively high; they were comparable to (or even lower than) what occurs in children fed soy milk formula. In addition, there are several reports of impaired immune responses in infants fed soy formula.  While it is too early to conclude that genistein impairs immunity, these findings are a potential cause for concern.

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