Daidzein is a phytochemical that is found in soybeans, peas, and other plants, such as kudzu and red clover. It is a polyphenol in a class of flavonoids known as isoflavones. Soy isoflavones have been widely studied for their effects on human health. These include antioxidant activity and protection against various types of cancer.
The major soy isoflavones include daidzein and genistein. These types of compounds have a structure similar to a mammalian estrogen. They also bind to estrogen receptors in animal and human cells. Thus, they are known as phytoestrogens, or estrogens from plants. They have been implicated as anticancer agents for hormone-based cancers, such as breast and prostate cancer.
Soybeans and soy products — such as soy flour, tofu, and soy milk — are major components of Asian diets. The rates of prostate and breast cancer are much lower in countries like Japan, compared to those in the West. When Japanese men emigrated to the United States and switched to American diets, their rates of prostate cancer greatly increased. It is hypothesized that this might be due to the shift away from a soy-based diet. Studies comparing the diets of people to their rates of cancer have found a correlation between consumption of soy and reduced levels of prostate cancer.
Laboratory studies have also shown daidzein to have anti-tumor effects against pancreas, colon, cervix, prostate, and breast cancer. A number of different types of studies have reported that soy isoflavones protected against breast cancers. Asian women have lower rates of breast cancer than Western women. Like with men, population studies have shown that when Asian women have moved to the West, the differences in breast cancer rates disappear after they switch their diet.
Another effect of daidzein is that it causes bone cells to grow in laboratory studies. This suggests that it might be helpful in protecting against the bone loss that occurs in women during menopause as hormone levels decline. The hormone estrogen had been used to help prevent bone loss, but research is showing it to have many undesirable side effects.
Kudzu root is used to make a traditional herbal medicine called Radix puerariae (RP). This contains daidzein. It has been used in traditional Chinese medicine for treating alcoholism, among other things. There is some evidence, from animal studies, that this isoflavone might have some effects against alcoholism.
Daidzein supplements are marketed for prostate protection. It is not clear how well they work, however. One should always check with a doctor before taking any herbal supplement, as they often interact with prescription drugs or other herbs. It may be best to obtain daidzein by eating soy products.