Equol was discovered in the 1980s; it is bacterially derived from daidzein, an isoflavone abundant in soy foods. Unlike the soy isoflavones, daidzein or genistein, it has a chiral center and therefore can occur as 2 distinct diastereoisomers, R and S. Humans have acquired an ability to exclusively synthesize S-equol from daidzein, and it is significant that, unlike R-equol, the S enantiomer has a relatively high affinity for estrogen receptor beta. A newly isolated rod-shaped, gram-negative anaerobic bacterium from human feces, named Julong 732, was found to be capable of metabolizing the isoflavone dihydrodaidzein to S-equol under anaerobic conditions.

Isoflavones - Daidzen and Genistein, 1000 mg tablets, by Source Naturals

Isoflavones derived from soybeans have been the focus of scientific research for several decades. Studies have shown that isoflavones can bind to the same receptor sites as estrogen. Soybeans are a significant dietary source of isoflavones; however, the amount of soy foods necessary to meet the body's needs can be difficult to incorporate into today's diet. In Asia, where soy is a staple, the daily isoflavone intake can be up to 20 times that of a Western diet. Source Naturals isoflavone-rich soybean powder yields a consistent standardized isoflavone content. This unique chemical-free process requires approximately 400 pounds of soybeans to yield just one pound of finished product.
 

Supplement Facts:
Isoflavone-Rich - 2 g
Soybean Powder (Soylife) Yielding:
   Daidzein - 34 mg - converts into equol
   Glycitein - 20 mg
   Genistein - 8 mg
   Total Isoflavones - 62 mg

Equol and hair loss or growth
As of 2015, I am not aware of good research with equol supplements to determine if this nutrient has an influence on hair growth or is as effective in vivo DHT blocker.

Will producing equol potentially help with male pattern baldness? If equol is created by soy plus something, what is the something that provides the bacteria environment for it? Is green tea that missing factor?
   Long term human studies are required to determine the role of equol in male pattern baldness, not enough research is available at this time to know its role in hair growth. It appears that vegetarians have a higher levelin their body, but the specific fruits, vegetables, legumes, etc that influence this is not yet clear to me.

Breast cancer
BMC Cancer. 2013. Equol enhances tamoxifen's anti-tumor activity by induction of caspase-mediated apoptosis in MCF-7 breast cancer cells.

Cervical cancer
Anticancer Res. 2014. Equol induces mitochondria-mediated apoptosis of human cervical cancer cells.

Prostate cancer
I am not aware of human clinical studies with equol supplements regarding the prevention or treatment of prostate cancer.

Asian Pac J Cancer Prev. 2013. Influence of isoflavone intake and equol-producing intestinal flora on prostate cancer risk. A traditional Japanese meal, high in soybean products or isoflavones, may be associated with a decreased risk of PCa. Equol, which is converted from daidzein by human intestinal flora, is biologically more active than any other isoflavone aglycone. We reviewed not only recent epidemiological studies on association of isoflavones with PCa risk, but also recent research on human intestinal bacteria responsible for converting daidzein into equol. Studies were systematically searched from the database published within the last 5 years of from 2008-2012. Five out of 6 articles showed significant association of isoflavones with a decreased risk of PCa, and two of them consistently showed that equol-producers carry a significantly reduced risk of PCa. Furthermore, 5 human intestinal bacteria that can convert daidzein into equol were identified in the last 5 years. If equol can reduce risk of PCa, a possible strategy for reducing the risk of PCa may be to increase the proportion of equol-producers by changing the intestinal flora to carrying an equol-producing bacterium with dietary alteration or probiotic technology.

Vegetarians
Method of defining equol -producer status and its frequency among vegetarians.
J Nutr. 2006.
7-Hydroxy-3-(4'-hydroxyphenyl)-chroman ( S- equol ) is a specific end-metabolite formed in the biotransformation of the dietary soy isoflavones daidzin and daidzein by intestinal bacteria. The frequency of equol production varies among individuals and populations, and it is suggested that the efficacy of soy foods differs depending on the ability of an individual to produce equol. To develop a standardized approach to define equol -producer status that can be universally adopted to differentiate these 2 distinct populations, we measured isoflavones in serum and urine collected from a cohort of 41 healthy adults, comprising 29 vegetarians and 12 nonvegetarians, after consuming 2 x 250 mL/d soy milk on 3 consecutive days. The frequency of equol producers in the vegetarians was 59%, similar to the reported frequency in Japanese adults consuming soy, and much higher than for nonvegetarian adults (25%), suggesting that dietary components other than soy influence equol synthesis by intestinal bacteria.

Bioavailability, absorption and physiology
The nonsteroidal estrogen equol occurs as diastereoisomers, S and R, both of which have significant biological actions. S-(–)equol, the naturally occurring enantiomer produced by 20–30% of adults consuming soy foods, has selective affinity for estrogen receptor-β, whereas both enantiomers modulate androgen action. Both enantiomers are rapidly absorbed, attain high circulating concentrations, and have a similar terminal elimination half-life of 7–8 h. American Journal of Clinical Nutrition, October 2009.

Equol research
S-Equol, a potent ligand for estrogen receptor ß, is the exclusive enantiomeric form of the soy isoflavone metabolite produced by human intestinal bacterial flora.
American Journal of Clinical Nutrition, 2005
Because it was unclear which enantiomer was present in humans, our objectives were to characterize the exact structure of equol, to examine whether the S- and R-equol enantiomers are bioavailable, and to ascertain whether the differences in their conformational structure translate to significant differences in affinity for estrogen receptors. Results: Our studies definitively establish S-equol as the exclusive product of human intestinal bacterial synthesis from soy isoflavones and also show that both enantiomers are bioavailable. S-equol has a high affinity for estrogen receptor ß, whereas R-equol is relatively inactive. Conclusions: Humans have acquired an ability to exclusively synthesize S-equol from the precursor soy isoflavone daidzein, and it is significant that, unlike R-equol, this enantiomer has a relatively high affinity for estrogen receptor beta.

Gut bacterial metabolism of the soy isoflavone daidzein: exploring the relevance to human health.
Exp Biol Med. 2005.
Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA
The indigenous intestinal microflora are involved in a variety of processes within the human body, and are important for maintaining host health. As such, interindividual differences in the ability to harbor certain intestinal bacteria might be associated with interindividual differences in health and/or disease susceptibility. In the last decade there has been considerable interest in phytoestrogen intakes in relation to human health. Daidzein, an isoflavone phytoestrogen found in soy, is metabolized to equol and O-desmethylangolensin (O-DMA) by intestinal bacteria. The specific bacterium/bacteria responsible for equol and O-DMA production in humans have yet to be identified definitively, but in vitro and animal studies have suggested that equol and O-DMA are more biologically active than their precursor daidzein. Interestingly, substantial interindividual differences in daidzein metabolism exist; following soy or daidzein consumption, approximately 30%-50% of the human population produce equol, and approximately 80%-90% produce O-DMA. Observational and intervention studies in humans have suggested that the ability to produce equol and O-DMA may be associated with reduced risk of certain diseases including breast and prostate cancers.

Higher consumption of green tea may enhance equol production.
Asian Pac J Cancer Prev. 2003.
Our previous case-control study revealed that Japanese living in Japan and Koreans living in Korea can be divided into equol producers who have an ability to metabolize daidzein to equol and non-producers, and that the incidence of prostate cancer is higher in the latter group. In the present study, we examined relationships between type of food intake and the capacity for equol production in Japanese subjects. The subjects were the individuals analyzed for the ability to produce equol in our previous study and newly registered cases. From 2000 to 2002, 276 hospitalized patients were interviewed face-to-face and blood samples were collected before breakfast. These included 122 patients with prostate cancer and 154 age-matched controls. The frequency of equol producers (0.5 ng/ml or more) among cases and controls was 29% and 45%, respectively. The consumption of soybeans and green tea were significantly higher in equol producers than in the non-producers. By contrast, the consumption of selenium and fiber was significantly lower in equol producers. Our results suggest that higher consumption of soybean and green tea are strongly related to the establishment of a capacity for equol production.

Estrogenicity of the isoflavone metabolite equol on reproductive and non-reproductive organs in mice.
Biol Reprod. 2004.
Equol, a metabolite of the phytoestrogen daidzein, is present at significant levels in some humans who consume soy and in rodents fed soy-based diets. Equol is estrogenic in vitro, but there have been limited studies of its activity in vivo. We evaluated equol effects on reproductive and non-reproductive endpoints in mice. Our results indicate that equol is a weak estrogen with modest effects on endpoints regulated by estrogen receptor alpha when present at serum levels seen in rodents fed soy-based diets, but quantities present in humans may not be sufficient to induce estrogenic effects, although additive effects of equol with other phytoestrogens may occur.

Comparisons of percent equol producers between prostate cancer patients and controls: case-controlled studies of isoflavones in Japanese, Korean and American residents.
Jpn J Clin Oncol. 2004.
Our previous case-control study revealed that the Japanese residents in Japan could be divided into those who are able to degrade daidzein, a soybean isoflavone, to equol and those without this ability, and that the incidence of prostate cancer is higher in the latter group. We recently conducted a similar case-control study involving not only Japanese residents in Japan but also Korean residents in Korea. The incidence of prostate cancer in Korean residents is known to be close to that of Japanese residents in Japan. On the other hand, American residents in the United States have a markedly higher incidence of prostate cancer as compared to Japanese residents in Japan. The number of subjects was 295 in Japan (133 patients and 162 controls), 122 in Korea and 45 in the United States (24 patients and 21 controls). The percentage of equol producers among patients and controls was 29% and 46% in Japan and 30% and 59% in Korea, respectively. The active isoflavone level was markedly lower and the percentage of equol producers was also lower (17% for patients and 14% for controls) for Americans as compared to the Japanese and Koreans. These results suggest that the ability of producing equol is closely related to the lower incidence of prostate cancer. The results also suggest that a diet based on soybean isoflavones will be useful in preventing prostate cancer.