IngredientsDaidzein (7-hydroxy-3-(4-hydroxyphenyl)-4H-chromen-4-one) is a naturally occurring compound found in soybeans and other legumes, and structurally belongs to a class of compounds known as isoflavones. Its IUPAC name is 4′,7-dihydroxyisoflavone. Daidzein is classified as an isoflavone — a subclass of flavonoids — with a chemical formula of C₁₅H₁₀O₄, featuring two phenolic rings connected by a three-carbon bridge.
Daidzein acts on the estrogen receptor and is non-steroidal in nature; hence it can also be called a non-steroidal phytoestrogenic compound. Daidzein and other isoflavones are produced in plants through the phenylpropanoid pathway of secondary metabolism and are used as signal carriers and in defense responses to pathogenic attacks.
Daidzein is an isoflavonoid derived from the shikimate pathway that forms an oxygen-containing heterocycle through a cytochrome P-450-dependent enzyme that is NADPH dependent. The biosynthesis of daidzein begins with L-phenylalanine and undergoes a general phenylpropanoid metabolic pathway where the shikimate-derived aromatic ring is shifted to the adjacent carbon of the heterocycle. The isoflavone synthase (IFS) enzyme was confirmed to be a P-450 oxygenase family member in 1999. IFS exists in two isoforms that can use both liquiritigenin and naringenin to give daidzein and genistein respectively.
The main sources of isoflavones are legumes from the family Fabaceae, namely soybean (Glycine max) as a source of daidzein, genistein, and glycitein, and red clover (Trifolium pratense) as a source of formononetin and biochanin A. Daidzein and other isoflavone compounds, such as genistein, are also present in plants and herbs like kwao krua (Pueraria mirifica) and kudzu. The kudzu root, which is utilized in traditional Chinese medicine and often incorporated into dietary supplements, contains daidzein in both its aglycone and glucoside forms.
Phaseolus vulgaris (common beans) has a daidzein content of 23.2 mg/kg, while both mung beans (Vigna radiata) and lima beans contain daidzein at a concentration of 0.3 mg/kg.
Genistein, daidzein, and glycitein (and their different chemical forms) comprise approximately 50%, 40%, and 10%, respectively, of total isoflavone content in soy, although there is considerable variation in this ratio among soybean varieties and foods produced from soybeans. According to USDA data, total isoflavones in soybeans are generally 37 percent daidzein, 57 percent genistein, and 6 percent glycitein. Soy germ contains 41.7 percent daidzein.
Isoflavones are contained in soybean or soy foods in two chemical forms: aglycones (unconjugated form) and glucosides (bound to a sugar molecule). The main dietary source of daidzein is its biologically active glucoside, daidzin. In soybeans and unfermented soy foods, isoflavones occur almost entirely as glycosides. Fermentation or digestion of soybeans or soy products results in the release of the sugar molecule from the isoflavone glycoside daidzin, leaving the isoflavone aglycone daidzein.
Daidzein can be found in soy-derived food products such as soy-based infant formulas, soy flour, textured soy protein, soy protein isolates, tofu, tempeh, and miso. The daidzein content of these products is quite variable: the daidzein amount is 22 mg in a half cup of miso, 15 mg in 3 ounces of tempeh, 8 mg in 3 ounces of tofu, and 7 mg in one cup of soy milk. The Asian population can consume up to 50 mg of isoflavones per day, whereas in Western countries consumption is less than 2 mg.
Beyond soy-based foods, daidzein is also present in substantial quantities in a variety of nutritional supplements, muscle-building shakes, sports beverages, and infant formulas. Dietary supplements containing daidzein are available in the US without a prescription. These products are not standardized, and the amounts of soy isoflavones they provide may vary considerably.
Historically, daidzein and soy-rich foods have been integral to traditional Asian medicine, particularly within Chinese and Japanese cultures. For centuries, these cultures have utilized soy-based remedies to promote general well-being and address specific health concerns.
Kudzu (Pueraria lobata) root extracts and flowers contain isoflavones including puerarin and daidzin. Kudzu is used in traditional Japanese and Chinese medicine to treat alcohol hangover and alcohol substance use disorder. Kudzu has been widely used in the treatment of cardiovascular diseases, diabetes, osteonecrosis, and neurodegenerative diseases in traditional Chinese medicine; the active ingredients of the Pueraria lobata flowers and root are the isoflavone derivatives puerarin, daidzin, and daidzein.
In traditional Asian cuisines, fermented soy has been a staple for centuries. In Japan, natto was used as a spring tonic, believed to strengthen digestion and circulation.
It is important to note that the isolation and chemical characterization of daidzein as a discrete compound is a modern scientific achievement; historical use was of whole soy foods and preparations, not isolated daidzein. The association of daidzein specifically with the observed traditional benefits of soy was established through twentieth-century phytochemical research.
Daidzein has attracted significant attention due to its ability to bind estrogen receptors (ERs) and modulate estrogenic signaling pathways. Its structural similarity to 17β-estradiol (E2) allows it to function as a phytoestrogen with selective estrogen receptor modulator (SERM)-like properties. Daidzein exhibits tissue-specific agonist or antagonist activities depending on the receptor subtype expression and cellular context.
Found abundantly in soybeans and red clover, daidzein exhibits SERM-like activity, favoring ERβ over ERα, which underlies its tissue-specific effects. Isoflavones exert their effects through interaction with estrogen receptors α and β, with higher binding affinity to ERβ compared to ERα. ERα is known to promote cell growth and differentiation, while ERβ is relevant in cytostatic and differentiation activities and counters the proliferative effects of ERα in mammary cancer cells. This indicates that the differential expression of ERs α and β determines the induction or inhibition of apoptosis.
Daidzein also has ER-independent biological activities, such as oxidative damage reduction acting as an antioxidant, immune regulation as an anti-inflammatory agent, and apoptosis regulation, directly linked to its potential anticancer effects.
Besides having estrogenic activity, isoflavones have non-hormonal effects such as inhibition of aromatase activity, downregulation of protein tyrosine kinases, and modulation of gene expression.
At low concentrations, daidzein can also induce cell proliferation via G protein coupled estrogen receptor 1 (GPER1) by stimulating cAMP production, intracellular Ca²⁺ mobilization, and cSrc activation. Subsequently, the transactivation of the epidermal growth factor receptor (EGFR) is triggered, leading to an activation of downstream signaling pathways such as PI3K/Akt and MAPK/ERK.
Daidzein activates multiple signaling pathways leading to cell cycle arrest and apoptosis as well as antioxidant and anti-metastatic effects in malignant cells.
Daidzein can be converted by intestinal microbiota into a number of substances, such as O-desmethylangolensin (O-DMA), dihydrodaidzein, and 7-hydroxyisoflavan. Gut microorganisms play a key role in the in vivo metabolism of dihydrodaidzein, in which it can be generated from daidzein and further converted into the more active equol.
Equol is considerably more estrogenic than daidzein. It has been reported that equol is 100-fold more potent than daidzein in stimulating an estrogenic response. Equol is also stronger than daidzein at competing with ³H-estradiol for binding to the estrogen receptor, suggesting that equol has a higher affinity for ER. It has also been demonstrated to be a more effective antioxidant than daidzein or genistein.
There is interindividual difference in the potential for S-equol production, with around half of the Asian adult population and one-third of the Western adult population being S-equol producers. The clinical effectiveness of soy isoflavones may be limited by the ability to transform soy isoflavones to the more potent estrogenic metabolite equol. High variability in equol production is attributable to interindividual differences in the composition of the intestinal microflora; only approximately one-third to one-half of the population is able to metabolize daidzein to equol.
Upon consumption of isoflavone-rich foods, daidzein has poor bioavailability and low water solubility. Glycosidic isoflavones are not readily bioavailable because of the sugar-binding moiety that prohibits enterocyte crossing. Thus, hydrolysis, usually mediated by intestinal bacteria, is required for gut absorption and bioavailability. On hydrolysis, unconjugated aglycones are produced, which can be further metabolized into equol (from daidzein). In the body, these compounds can undergo reconjugation to glucuronides and are excreted in the urine.
Pharmacokinetic studies reveal moderate bioavailability and interindividual variability due to gut microbiota metabolism. Researchers have developed novel formulations of daidzein to improve its aqueous solubility and bioavailability. Self-emulsified daidzein, poly(lactic-co-glycolic) acid daidzein nanoparticles, nanoemulsion, nanoemulsion gel, and co-crystals are among the approaches explored.
Menopause is characterized by a decline in estrogen levels, leading to symptoms such as vasomotor instability, osteoporosis, and increased cardiovascular and cognitive risk. Concerns regarding the long-term safety of hormone replacement therapy (HRT), including elevated risks of cancer and cardiovascular events, have prompted interest in alternative therapies. Daidzein and genistein, plant-derived compounds structurally similar to 17β-estradiol, are capable of binding estrogen receptors.
Clinical trials show that daidzein and genistein, especially in equol-producing individuals, can reduce vasomotor symptoms such as hot flashes and night sweats. While results across studies vary, consistent findings support their safety and modest efficacy, particularly for women unable or unwilling to use HRT.
Equol is produced from the isoflavone daidzein by intestinal bacteria, mainly in the large intestine. A meta-analysis by Daily et al. (2019) included five studies with a total of 728 menopausal women between 50.5 and 58.5 years old and concluded that women who are not able to produce equol could benefit from equol supplementation. Conversely, women who were already equol producers did not obtain any additional benefit from supplements of equol or isoflavones.
Evidence strength: Clinical evidence supports the safety of dietary daidzein and highlights its potential benefits for, to a lesser extent, menopausal symptom relief. Results are mixed and modest compared to pharmaceutical HRT; outcomes are strongly influenced by equol-producer status.
In postmenopausal women, current meta-analytic evidence indicates that soy isoflavones are effective in improving bone mineral density and reducing the symptoms of menopause predominantly hot flashes, and they improve oxidative stress, glycemia, and lipid abnormalities.
Evidence indicates that isoflavones exerted little influence over bone mineral density and thus over bone health during menopause, although not all studies observed the same effect. Discrepancies among studies could be due to the duration of treatment, the type of isoflavone, its dose, and the diet. Regarding specific isoflavones, genistein, alone or in combination with daidzein, improved bone density and bone turnover in women after menopause.
A randomized controlled trial found that supplementation with soy isoflavones increased calcium retention capacity in postmenopausal women regardless of their equol-producing capacity. Daidzein has emerged as particularly promising, outperforming genistein in preventing trabecular bone loss in ovariectomized rats.
Evidence strength: Evidence from human trials and meta-analyses is mixed. Some positive effects on bone mineral density have been observed, particularly with combined genistein and daidzein, but effect sizes are inconsistent across studies. Most supportive evidence comes from postmenopausal women. Animal data are more consistently positive.
Isoflavone-containing soy protein can lower total cholesterol, LDL cholesterol, and triglyceride serum levels. Analysis found that consumption of soy isoflavones brought about a statistically significant reduction in total and LDL cholesterol, while simultaneously demonstrating no significant effects on HDL and TAG (triacylglycerols).
A meta-analysis of 14 randomized controlled studies reported a reduction in circulating C-reactive protein (CRP) — an inflammation marker associated with increased cardiovascular risk — following soy isoflavone intake in postmenopausal women with elevated baseline CRP concentrations (>2.2 mg/L).
Equol and O-DMA producers had more favorable cardiovascular risk profiles than non-producers in prehypertensive postmenopausal women. Soy foods are rich sources of isoflavones including daidzein and genistein and are traditionally consumed by Asian populations. Human intervention studies assessing the effects of soy or isoflavones on cardiovascular risks have reported inconsistent findings. Studies have suggested that interindividual differences in gut bacteria metabolism of isoflavone daidzein to equol or O-DMA might explain these discrepancies.
Evidence strength: Neither the efficacy of isoflavone content in soy preparations nor the relevance of baseline lipid profiles has been well delineated, nor has a dose-response relationship been confirmed. The lipid-lowering effect (total and LDL cholesterol) from meta-analyses is statistically significant but of modest clinical magnitude; effects on HDL and triglycerides are not significant.
Emerging evidence from epidemiological studies has shown an association between higher intake of soy isoflavones and reduced risk of type 2 diabetes (T2D) and its associated health risks. Daidzein, a soy isoflavone, has been found to have promising therapeutic potential in managing T2D pathophysiology. Many studies have reported the prophylactic effect of daidzein on the improvement of hyperglycemia, insulin resistance, dyslipidemia, obesity, and inflammation.
The influence of soy isoflavones on glucose levels has been shown to be statistically insignificant. However, the ability of both extracted isoflavone and soy protein with isoflavones to modulate the lipid profile suggests benefits in preventing cardiovascular events in people with type 2 diabetes.
A meta-analysis revealed statistically insignificant reduction in fasting glucose, insulin, HbA1c, and HOMA-IR after consumption of soy isoflavones.
A registered clinical trial (NCT00951912) examined purified daidzein (50 mg/day) versus placebo in prediabetic or diabetic women over 6 months. One hundred and eighty eligible women aged 30–70 years (without any treatment of diabetic drugs) were randomly allocated into three arms: Placebo (10g isolated soy protein); Genistein (10g ISP + 50mg genistein); or Daidzein (10g ISP + 50mg daidzein) per day for 6 months. Fasting glucose, lipids, insulin, inflammation markers, and post-load glucose and insulin were evaluated at 0, 3, and 6 months.
Evidence strength: Meta-analytic data do not support a statistically significant effect of soy isoflavones on glycemic markers. Effects on lipids in diabetic populations are more encouraging. Animal and in vitro data show mechanistic potential, but clinical translation remains limited.
Low risk of breast cancer is observed among females consuming a moderate quantity of soy throughout their life. This epidemiological observation has generated significant laboratory research interest.
The beneficial effect of dietary soy food intake, especially for women diagnosed with breast cancer, is controversial, as in vitro data has shown that soy isoflavones genistein and daidzein may stimulate the proliferation of estrogen-receptor-alpha positive breast cancer cells. The low bioavailability and extensive metabolism of soy-active components limit their clinical application. The impact of daidzein and its metabolites on estrogen-dependent anti-apoptotic pathways has been evaluated in breast cancer cells. In estrogen receptor α-positive breast cancer cells treated with daidzein and its metabolites, ERα activation and Neuroglobin levels were evaluated.
Currently available data suggest that breast cancer survivors should not be further discouraged from consuming soy foods in moderation. Moreover, in a pooled analysis of three large prospective cohort studies, soy isoflavone intake ≥10 mg/day was associated with a 25% reduced risk of tumor recurrence in breast cancer survivors.
Evidence strength: Epidemiological data from Asian populations suggest an inverse association between lifelong soy food intake and breast cancer risk. However, in vitro data on ERα-positive breast cancer cells show complex and sometimes opposing effects depending on the concentration and hormonal milieu. High-dose supplementation in women with hormone-sensitive breast cancer is not supported by current evidence. Clinical trial data for daidzein as an isolated agent are lacking.
Daidzein did not increase metastasis to lymph nodes and acted as a radiosensitizer for prostate tumors in preclinical (mouse) experiments. Daidzein inhibited cell growth and enhanced radiation in vitro, but at doses higher than genistein or soy.
Daidzein non-metabolizers were found to be significantly more common in a prostate cancer patient group compared to controls. The poorly differentiated cancer patient group included a significantly lower percentage of daidzein metabolizers. These findings revealed that equol itself or some unknown factor regulating the metabolism of daidzein is involved in the biology of prostate cancer.
Human diet has been reported to have a strong impact on the genesis of prostate cancer. Several studies have shown nutrients such as phytoestrogens to possess anticancer properties.
Evidence strength: Epidemiological data suggest a relationship between daidzein metabolism (equol production) and prostate cancer risk. Preclinical data are encouraging but largely derived from cell lines and animal models. Definitive human clinical trial data for daidzein in isolation are not available.
Daidzein has emerged as a promising alternative to hormone replacement therapy (HRT) for ameliorating estrogen deficiency, including its neurological consequences. Research in ovariectomized rats showed daidzein effectively increased the volume and total number of pyramidal neurons in the CA1 region, and the expression of ERα, ERβ, BDNF, and Bcl-2 genes.
In vitro, in silico, and in vivo studies demonstrate the ability of daidzein to modulate estrogenic pathways, inhibit oxidative stress, and influence reproductive and neurological function.
Evidence strength: Evidence for neuroprotection is predominantly from animal (ovariectomized rodent) models and in vitro studies. Robust human clinical trial data are absent. This remains a preliminary area of investigation.
Daidzein has been described as inhibiting the aldehyde-dehydrogenase-2 enzyme (ALDH2), and reducing alcohol use in clinical pilot studies. Some isoflavones, especially daidzin and daidzein, have been reported to inhibit the aldehyde-dehydrogenase-2 enzyme (ALDH2). This mechanism is the pharmacological basis for the traditional use of kudzu preparations for alcohol-related complaints.
Evidence strength: Preliminary, based on mechanistic studies and small pilot trials. Not established as a clinical intervention.
Dosages of various forms of soy in clinical studies evaluating various uses have included 22.7 to 300 mg/day of soy isoflavones, up to 40 g/day of isolated soy protein, 120 g/day of dietary soy foods, 50 to 150 g/day of unfermented soy foods, up to 450 mg/day of genistein, and up to 300 mg/day of daidzein.
In the clinical trial NCT00951912, the daidzein arm received 10g isolated soy protein plus 50 mg daidzein per day for 6 months.
Regarding commonly available supplement forms, dietary supplements containing daidzein are available in the US without a prescription. Daidzein is available as:
Acute oral toxicity studies following OECD guideline TG 423 indicated that doses up to 1000 mg/kg did not result in significant changes in hematology, clinical biochemistry, or kidney function, although some alterations in serum glucose, lipids, and relative organ weights were observed.
The ingestion of soy isoflavones is considered safe; the most common adverse effects are gastrointestinal (diarrhea) and more rarely headache, prolonged menstrual period, amenorrhea, dizziness, and musculoskeletal complaints.
Daidzein may cause a variety of adverse reactions, including bloating, colitis, constipation, diarrhea, sleeplessness, itching, nausea, skin rash, and changed thyroid hormone levels.
At dietary levels, daidzein is generally safe, although high-dose supplementation is discouraged in individuals with hormone-sensitive cancers.
The chemical composition of daidzein is analogous to mammalian estrogens, and it has a dual-directional purpose by substituting or hindering estrogen and the estrogen receptor complex. Daidzein thus exerts shielding effects against diseases associated with the control of estrogen, such as breast cancer, diabetes, osteoporosis, and cardiovascular disease. However, the SERM-like properties of daidzein mean its effects in hormone-sensitive tissues are context-dependent, and caution has been expressed regarding supplementation in individuals with known hormone-sensitive malignancies.
In some studies, a detrimental effect on thyroid function was observed, specifically in the first 3 months of supplementation. This effect was observed in studies where significant improvement was also seen in glucose metabolism but not in lipid parameters.
Infants are able to absorb isoflavones, and infants fed soy formula were demonstrated to have plasma isoflavone blood levels exceeding those of Japanese adults several-fold. Soy-based infant formula can result in plasma concentrations of isoflavones in infants that are 13,000–22,000 times higher than endogenous estrogen concentrations in infants. This observation has been the subject of ongoing regulatory and scientific scrutiny.
Daidzein, a principal isoflavone in soybean, in higher doses may inhibit CYP1A2 activity in vivo, and physicians should be aware of potential drug-food interactions. CYP1A2 is a major drug-metabolizing enzyme involved in the metabolism of many pharmaceutical agents including theophylline, certain antidepressants, and antipsychotics. In a human study examining this interaction, inhibition of theophylline metabolism by daidzein was specifically investigated.
Phytoestrogens, including daidzein-containing preparations, may interact with anticoagulant agents. For instance, both American ginseng and phytoestrogens may increase anticoagulation, requiring monitoring. Similarly, aspirin-containing combinations and choline magnesium trisalicylate in combination with phytoestrogens both may increase anticoagulation effects.
The phytoestrogens daidzein and equol inhibit the drug transporter BCRP/ABCG2 in breast cancer cells, suggesting a potential chemosensitizing effect. This transporter inhibition has implications for the bioavailability of co-administered drugs that are BCRP substrates.
Interindividual differences in gut bacteria metabolism of isoflavone daidzein to equol or O-DMA may explain discrepancies in observed health outcomes. The daidzein-metabolizing phenotype appears to remain stable within an individual over time, suggesting that physiologic effects could have long-term impact on the health of the human host. This means that two individuals taking the same dose of daidzein may experience substantially different biological effects depending on their gut microbiome composition.
Health conditions that Daidzein may help support.
Daidzein is a soy isoflavone that binds bone estrogen receptors and is the metabolic precursor to equol, a more potent bone-active phytoestrogen. Animal research demonstrated daidzein was more efficient than genistein in preventing ovariectomy-induced bone loss. Clinical trials of isoflavone preparations containing daidzein show positive effects on BMD in postmenopausal women.
Daidzein is a soy isoflavone with documented ERβ-preferential binding that acts as a weak phytoestrogen and SERM. It is metabolized by gut bacteria to equol (in ~30–50% of individuals), which has stronger estrogenic activity. Multiple RCTs show soy isoflavones including daidzein provide modest reduction in menopausal vasomotor symptoms.
Daidzein is a soy isoflavone metabolized to the more potent equol by gut flora in some individuals. Clinical trials, particularly in equol-producers, show reduction in vasomotor symptoms including hot flashes. Evidence is modest and population-dependent based on individual microbiome composition.
Daidzein is a key soy isoflavone and the direct metabolic precursor to equol, a more potent phytoestrogen. A meta-analysis confirmed that equol producers who convert daidzein to equol achieve significantly better hot flash reductions. Daidzein-containing soy isoflavone preparations are used in RCTs for menopausal vasomotor symptom management.
Daidzein is a soy isoflavone shown to stimulate osteoblast differentiation and inhibit osteoclast activity via multiple signaling pathways. Clinical trials of daidzein-containing isoflavone mixtures have shown reduced lumbar spine bone loss in postmenopausal women. It is the most widely studied soy phytoestrogen for bone health alongside genistein.
Daidzein is the second major soy isoflavone with documented phytoestrogenic, anti-androgenic, and insulin-sensitizing properties. It is precursor to equol (a potent anti-androgen) in gut-metabolizing individuals. Studies suggest benefits for androgen excess, insulin resistance, and SHBG in PCOS.
Daidzein is an isoflavone phytoestrogen found in soybeans and red clover that binds ERβ with SERM-like activity. Clinical trials demonstrate that daidzein, especially in equol-producing individuals, reduces vasomotor symptoms including hot flashes and night sweats during the menopausal transition.
Body systems that Daidzein may help support.
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