8-Prenylnaringenin

8-Prenylnaringenin

Identity, Chemical Character, and Natural Sources

8-Prenylnaringenin (8-PN; also known as flavaprenin, (S)-8-dimethylallylnaringenin, hopein, or sophoraflavanone B) is a prenylflavonoid phytoestrogen. More precisely, 8-prenylnaringenin is a prenylated flavanone — a type of flavonoid characterized by a naringenin backbone with a 3,3-dimethylallyl (prenyl) substituent at the 8-position — possessing the molecular formula C₂₀H₂₀O₅ and a chiral center at C-2. The compound structurally belongs to the group of prenylated flavonoids and has been shown to be a potent phytoestrogen.

8-Prenylnaringenin is a natural compound biosynthesised in the lupulin glands of the hop inflorescences. It is the substance with the highest estrogenic activity known so far in the plant kingdom. This compound is primarily derived from the female inflorescences (cones) of hops (Humulus lupulus L.), where it constitutes approximately 0.1% of dry matter in lupulin glands, and is also present in trace amounts in beer as well as in over 20 ethnomedicinal plants, including species from genera like Sophora and Citrus.

Hop (Humulus lupulus L.) is a vine belonging to the genus Humulus from the family Cannabaceae. The strongest known phytoestrogen so far is 8-prenylnaringenin (8-PN), which along with 6-prenylnaringenin (6-PN), 6,8-diprenylnaringenin (6,8-DPN) and 8-geranylnaringenin (8-GN) are fundamental for the potent estrogen activity of hops.

There is another compound, 8-isopentenylnaringenin, also known as sophoraflavanone B, from Sophora flavescens, that could properly be called 8-prenylnaringenin by scientific naming convention. The principle estrogen from hops is the 1:1 racemate, (±)-8-prenylnaringenin. This compound is known in the English hop literature as 8-prenylnaringenin or hopein.

Biosynthetic Origin and Precursor Relationships

Xanthohumol is formed in lupulin glands by a specialized branch of flavonoid biosynthesis that involves prenylation and O-methylation of the polyketide intermediate chalconaringenin. Through a chemical isomerization, it gives rise to the major estrogen of hops identified as the 1:1 racemate (±)-8-prenylnaringenin (8-PN), along with the racemic 6-prenylnaringenin (6-PN). In humans 8-PN has been shown to derive from isoxanthohumol through activation by intestinal microflora or by liver cytochrome P450 enzymes. Hence, the estrogenically inactive xanthohumol possesses an estrogenic potential through its conversion to isoxanthohumol and then to 8-PN.

Of particular interest is the metabolism of isoxanthohumol, particularly its biotransformation by gut microbiota to 8-prenylnaringenin (8-PN), a potent phytoestrogen, which indicates the complex nature of its biological activity and potential health implications. 8-PN can be produced from its precursor, xanthohumol, by the intestinal microbial community of some, but not all, humans in large quantities, suggesting that even moderate beer consumption might be able to induce health effects due to increased serum levels of 8-PN.

Pharmacokinetics and Bioavailability

Pharmacokinetic studies revealed that these flavonoids are conjugated rapidly with glucuronic acid. The bioavailability assay confirmed that 8-prenylnaringenin is five times more bioavailable than 6-prenylnaringenin in healthy humans who were given 500 mg of both compounds at once. It has been shown that human liver microsomes convert 8-prenylnaringenin to 12 metabolites, with (E)-8-(4''-hydroxyisopentenyl)naringenin (8-PN-OH) and (E)-8-(4''-oxoisopentenyl)naringenin (8-PN=O) being among the most abundant. These two major metabolites of 8-prenylnaringenin are themselves estrogenic in vitro.

Traditional and Historical Use

Hops, the resinous inflorescences of the twining vine Humulus lupulus L. (Cannabaceae), are used today primarily for their bitter and aromatic properties in the manufacture of beer. In addition, hop preparations are sold in health-food stores in the U.S. for the treatment of anxiety and insomnia, and are sold in pharmacies in Europe for similar purposes. It is appreciated in phytotherapy, for its sedative, digestive, anti-inflammatory, and other effects.

Female hop-pickers suffered from disturbances in their menstrual cycles during the hop harvests, and this phenomenon led to the assumption that hops exerted estrogenic activities. At that time, hop baths were applied as a traditional therapy for several gynecological difficulties. A recurring suggestion over the years has been that hops, which have been used for centuries as a preservative and as a flavouring agent in beer, have powerful oestrogenic activity. When hops were picked by hand, menstrual disturbances amongst women pickers were reportedly common.

Hop extract was reported to be efficient in reducing menopause-associated hot flushes in women. Moreover, hop baths have been used for treatment of gynecological disorders over the years. Other traditional applications of hops as a stomachic, antibacterial, and antifungal remedy have been supported by in vivo and/or in vitro investigations.

The estrogenicity of hops was initially attributed to xanthohumol without any reported scientific data. 8-PN had been originally identified from hops as early as 1984 but had been forgotten thereafter. The active substance, 8-PN, which is responsible for the estrogenic effect, was definitively identified in 1999 by Milligan.

Key Constituents and Active Compounds in Hops

Humulus lupulus is a source of miscellaneous compounds, including essential oils, bitter acids, and polyphenols, and many of them exert biological activities. The chalcone xanthohumol (XH) is the major prenylated flavonoid in spent hops. Other less abundant but important bioactive prenylated flavonoids are isoxanthohumol (IX), 8-prenylnaringenin (8-PN), and 6-prenylnaringenin (6-PN).

Xanthohumol (3′-[3,3-dimethyl allyl]-2′,4′,4-trihydroxy-6′-methoxychalcone) is the principal prenylated flavonoid of the female inflorescences of the hop plant, an ingredient of beer. Xanthohumol has been characterized as a 'broad-spectrum' cancer chemopreventive agent in in vitro studies, while 8-prenylnaringenin enjoys fame as the most potent phytoestrogen known to date. Xanthohumol also undergoes phase I metabolism in vivo to form isoxanthohumol, 8-PN, and 6-PN.

Mechanisms of Action

Estrogen Receptor Binding and Agonism

In a series of in vitro assays using recombinant human estrogen receptor (ER), 8-PN displayed a relative binding affinity (RBA) of approximately 0.1 to ERα and ERβ, when benchmarked against 17β-estradiol. This value far exceeded the RBA of other hop-derived flavonoids, including isoxanthohumol, which showed negligible receptor interaction. More critically, 8-PN was confirmed to act as a full agonist, activating estrogen-responsive promoters in both yeast assays and human Ishikawa endometrial cells.

8-PN is the most potent phytoestrogen known today, with only 70-fold lower affinity for the ERα receptor than the endogenous female reproductive hormone 17β-estradiol. 8-PN is not only one of the strongest plant-derived ERα ligands identified to date, but also shows a hormonal profile different from soy isoflavones, being over three times more powerful at ERα than ERβ activation. Genistein, daidzein, and equol demonstrate higher affinities for ERβ, whereas 8-PN has a higher affinity for ERα.

In silico modeling of ER binding further suggested that chain prenylation without an increase in molecular length, which enables 8-PN to fit into the hydrophobic pocket in the human ER, is responsible for the high agonist activity of 8-PN compared with naringenin. However, conflicting data were obtained in rat N46A-B14 cells derived from raphe nuclei region of the brain stably expressing a transgenic human ERβ along with an ERE–luciferase construct. In this test system, co-treatment of 8-PN with estradiol (E2) resulted in a slight but statistically significant inhibition of E2 impact, suggesting partial agonism as the mode of interaction for 8-PN with ERβ.

Studies on the endocrine properties of 8-PN have demonstrated that this compound is a natural selective estrogen receptor modulator (SERM) because its effect spectrum is not fully identical with that of estradiol (E2). The estrogenic activity of 8-prenylnaringenin in vitro was greater than that of established phytoestrogens such as coumestrol, genistein and daidzein.

Non-Genomic and Cellular Signaling

Under conditions of estrogen-dependent growth, treatment of MCF-7 human breast cancer cells with 8-PN induced a rapid and transient activation of the MAP kinase Erk-1 and Erk-2, with kinetics similar to those induced by 17β-estradiol (E2). 8-PN could trigger the MAP kinase pathway via dual c-Src kinase activation and association with ERα. Estrogen receptor exists in 2 forms, ERα and ERβ, which have multiple isoforms and exhibit distinct tissue expression patterns and functions. The two receptors have different effects on cell signaling in various tissues; for example, ERα activation is associated with cell proliferation and ERβ activation is associated with counteracting ERα-stimulated cell proliferation.

8-PN also induces the secretion of prolactin, and increases other estrogenic responses. More recently, a radioligand binding study showed enhancements in GABAA receptor activity by 8-PN. Several hop constituents are responsible for distinct effects linked to multiple biological targets, including hormonal, metabolic, inflammatory, and epigenetic pathways.

Scientific Evidence by Area of Use

Menopausal Vasomotor Symptoms (Hot Flushes)

8-Prenylnaringenin (8-PN) has been identified as a potent phytoestrogen in hops (Humulus lupulus) and there are claims that hop-containing preparations can reduce hot flushes. The site of action of 8-PN was investigated in a rat model of menopausal hot flushes, in which the tail skin temperature (TST) is increased after oestrogen withdrawal induced by ovariectomy. Daily subcutaneous administration of either 17β-oestradiol (E2; 4 μg/kg) or 8-PN (400 μg/kg) significantly reduced the elevated TST after 2 days of treatment. Subcutaneous co-administration of either E2 or 8-PN with the oestrogen receptor (ER) antagonist ICI 182,780 (200 μg/kg), which is thought not to cross the blood-brain barrier, completely blocked the effect of E2 and 8-PN on TST, indicating a peripheral site of action.

First pivotal randomized controlled trial (Heyerick et al., 2006): A prospective, randomized, double-blind, placebo-controlled study over 12 weeks was conducted with 67 menopausal women, who were administered a hop extract standardized on 8-PN (100 or 250 μg). The responses were determined by means of a modified Kupperman index (KI) and a patients' questionnaire. All groups, including placebo, showed a significant reduction of the KI both after 6 weeks and after 12 weeks. The hop extract at 100 μg 8-PN was significantly superior to placebo after 6 weeks (P=0.023) but not after 12 weeks (P=0.086). Administration of a hop extract standardized on 8-prenylnaringenin (daily dose of 100 μg) to post-menopausal women during 6 weeks and 12 weeks reduced discomforts and complaints associated with the menopause. In particular, rapid improvement of the incidence of hot flushes was evident.

Cross-over pilot study (Erkkola et al., 2010): A 16-week randomized, double-blind, placebo-controlled, cross-over study was conducted with 36 menopausal women. The participants were randomly allocated to either placebo or active treatment (hop extract standardized at 100 μg 8-prenylnaringenin per day) for a period of eight weeks, after which treatments were switched for another eight weeks. The Kupperman Index (KI), the Menopause Rating Scale (MRS) and a multifactorial Visual Analogue Scale (VAS) were assessed at baseline, and after eight and sixteen weeks.

Combination product study (FLAVIE study, 2023): A multicenter, prospective, open-label study enrolled 44 postmenopausal women suffering from moderate-to-severe hot flashes (≥5 daily or ≥35 weekly) to receive 54.4 mg standardized soy isoflavones (including 24.5 mg genistein and 16.3 mg daidzein), 100 µg 8-PN, and 1 mg melatonin once daily for 12 weeks. All four domains of the MENQoL questionnaire significantly improved at 4 weeks (P<0.05) and 12 weeks (P<0.001), affecting significantly the vasomotor, psychosocial, and physical spheres. Because this study used a combination product without a placebo arm, the individual contribution of 8-PN cannot be isolated from this result.

The results of RCTs of the hop flavonoid 8-prenylnaringenin are conflicting. The number of high-quality, large-scale human clinical trials is still low, and most studies use hop extract rather than pure 8-PN, making it difficult to attribute effects solely to 8-PN. Overall, the human clinical evidence for vasomotor symptoms is preliminary and promising, but remains limited by small sample sizes, the dominance of extract-based rather than purified-compound study designs, and the observation of significant placebo effects in available trials.

Bone Health and Osteoporosis

In vitro, 8-PN was shown to enhance differentiation and maturation of osteoblast and inhibit differentiation of osteoclast with intensities of response stronger than that observed with soy isoflavones. Several in vivo studies demonstrated that an oral supplementation with a standardized hop extract was able to prevent estrogen-deficiency-induced bone loss in osteoporotic rodent models. Moreover, in ovariectomized rats, supplementation with 68.4 mg/kg of body weight per day of 8-PN during twelve weeks improved bone biomechanical properties to the same degree as 0.7 mg/kg body weight per day of estradiol, while the two other phytoestrogens tested, genistein (60 mg/kg bw per day) and resveratrol (50 mg/kg bw per day), had no significant impact.

8-PN was studied in adult ovariectomized rats, an established animal model to mimic hormone-dependent osteoporosis in menopausal women. Results demonstrated that 8-PN can completely protect from ovariectomy-induced bone loss while exhibiting minimal, dose-independent trophic effects on uterus and endometrium. It is estimated that at equivalent bone-protective doses of 17β-estradiol and 8-PN, the phytoestrogen has a 10-fold lower stimulatory effect on uterus and endometrium.

First large human RCT on bone (2023): In a double-blind, placebo-controlled, randomized trial, 100 postmenopausal, osteopenic women were supplemented with calcium and vitamin D3 (CaD) tablets and either a hop extract (HE) standardized in 8-PN (n=50) or a placebo (n=50) for 48 weeks. Bone mineral density (BMD) and bone metabolism were assessed by DXA measurements and plasma bone biomarkers. In addition to the CaD supplements, 48 weeks of HE supplementation increased total body BMD (1.8 ± 0.4% vs. baseline, p<0.0001). Participant's quality of life (SF-36), gut microbiome composition, and short-chain fatty acid (SCFA) levels were also investigated.

However, in one rat model study, 8-PN at a cancer-safe dose did not cause fundamental improvements in osteoporotic bones, illustrating that results across animal models and dose regimens are not entirely consistent. The 2023 human RCT represents the strongest clinical evidence to date for a bone benefit, but it was conducted with a combined CaD background and was partially industry-affiliated; independent replication is needed.

Anticancer Activity

In an in vitro study, 8-PN and synthetic derivatives demonstrated anticancer properties. 8-PN is not only one of the strongest plant-derived ERα ligands identified to date, but shows a hormonal profile different from soy isoflavones, being over three times more powerful at ERα than ERβ activation. Treatment of MCF-7 human breast cancer cells with 8-PN induced a rapid and transient activation of the MAP kinase Erk-1 and Erk-2. 8-PN could trigger the MAP kinase pathway via dual c-Src kinase activation and association with ERα.

Prenylation at carbon-8 enhanced cytotoxicity (IC50 <10 µM/L) of naringenin, hesperidin, and quercetin-derived novel products on HeLa, HCC1954, and SK-OV-3 cancer cells in vitro. With 8-prenylnaringenin, good cellular uptake and enhanced anti-cancer effect were observed in human glioblastoma cells compared to non-prenylated naringenin. In contrast to naringenin, 8-prenylnaringenin is a potent hop-derived estrogenic compound, highlighting the importance of the prenyl group for hormonal activity.

All anticancer evidence for 8-PN currently derives exclusively from in vitro (cell culture) studies. There are no human clinical trials evaluating 8-PN for cancer prevention or treatment. The majority of 8-PN effects require such high concentrations that they cannot be reached by normal dietary exposure, only pharmacologically; thus, adverse impacts may also emerge. These findings are therefore preliminary and require substantial further investigation before any clinical conclusions can be drawn.

GABA_A Receptor Activity and Neuroprotection

A radioligand binding study showed enhancements in GABAA receptor activity by 8-PN. The broader sedative properties of hop preparations have been recognized in traditional European medicine and phytotherapy, though the sedative activity is still under investigation in order to recognize the active principles responsible for the neuropharmacological effects observed in laboratory animals, and their mechanism of action. Whether 8-PN specifically mediates the sedative effects of hop, as opposed to other hop constituents such as methylbutenol, remains unresolved in the scientific literature. Evidence is confined to in vitro binding studies and animal data.

Cardiovascular and Lipid Effects

These biological activities suggest that prenylflavonoids from hops have potential for application in cancer prevention programs and in prevention or treatment of (post-)menopausal 'hot flashes' and osteoporosis. Some preclinical and exploratory data suggest estrogen-related cardiovascular effects consistent with the broader pharmacology of ERα agonists, but numerous health benefits associated with a wide spectrum of biological activities including estrogenic, anticancer, neuroprotective, anti-inflammatory, and antimicrobial properties have been intensively studied, with potential applications such as as an alternative to hormone replacement therapy (HRT). At this time, no dedicated human clinical trials on cardiovascular endpoints with 8-PN have been reported in the peer-reviewed literature.

Dosage Forms and Doses Reported in Studies

Older women tend to take botanical supplements such as hops as natural alternatives to traditional hormone therapy to relieve menopausal symptoms. Especially extracts from spent hops, the plant material remaining after beer brewing, are enriched in bioactive prenylated flavonoids that correlate with the health benefits of the plant.

• Standardized hop extract (oral, menopausal symptoms): A prospective, randomized, double-blind, placebo-controlled study over 12 weeks used a hop extract standardized on 8-PN at doses of 100 µg or 250 µg per day.
• Standardized hop extract (oral, cross-over trial): A hop extract standardized at 100 μg 8-prenylnaringenin per day was examined for relief of menopausal discomforts.
• Combination supplement: One multicenter study used 100 µg 8-PN combined with 54.4 mg standardized soy isoflavones and 1 mg melatonin once daily for 12 weeks.
• Animal model (bone): In ovariectomized rats, supplementation with 68.4 mg/kg of body weight per day of 8-PN was used over twelve weeks for bone biomechanical assessment.
• Animal model (hot flushes): In a rat model, daily subcutaneous administration of 8-PN at 400 μg/kg significantly reduced elevated tail skin temperature.
• Human bioavailability study: In healthy humans, 500 mg of both 8-prenylnaringenin and 6-prenylnaringenin were administered simultaneously in a comparative bioavailability study.
• Clinical recommendation (Spanish Menopause Society, 2025): A hop extract containing 100 µg of 8-PN (8-prenylnaringenin) was identified as balancing effectiveness and side effects, making it a potential treatment for HRT.

Body Systems and Health Areas Associated with 8-PN

• Reproductive and endocrine system: The presence of 8-prenylnaringenin in hops may provide an explanation for the accounts of menstrual disturbances in female hop workers. As an estrogen, 8-PN has the potential to interact with the estrogen-signaling systems within the body, including the reproductive system.
• Vasomotor and thermoregulatory system: The mechanisms underlying menopausal hot flushes are poorly understood, although it is generally assumed they result from disturbances of thermoregulatory centres in the hypothalamus. Animal and clinical data support a role for 8-PN in modulating peripheral estrogen receptor activity to reduce skin temperature surges.
• Skeletal system: 8-Prenylnaringenin is the phytoestrogen with the highest affinity for estrogen receptor-α (ERα), which is required to maintain bone mineral density (BMD).
• Central nervous system: Both GABAergic activity and potential neuroprotective properties have been investigated in preclinical models, though clinical evidence is lacking.
• Breast tissue: Prenylflavonoids from hops, including 8-PN, are ingredients in some breast enlargement supplements, though there is no evidence of its effectiveness for this purpose.
• Gut microbiome: Gut microbiome composition and short-chain fatty acid (SCFA) levels were investigated in the context of 8-PN supplementation and the microbial conversion of isoxanthohumol to 8-PN has direct implications for individual variability in biological response.

Safety Considerations

Uterotrophic Activity

A strong stimulation of the uterus by 8-PN may be associated with the occurrence of adverse effects (e.g., bleeding) and may increase the risk of carcinogenesis. Animal data demonstrate that 8-PN can completely protect from ovariectomy-induced bone loss while exhibiting minimal, dose-independent trophic effects on uterus and endometrium. It is estimated that at equivalent bone-protective doses of 17β-estradiol and 8-PN, the phytoestrogen has a 10-fold lower stimulatory effect on uterus and endometrium. However, this finding is from animal models; clinical uterine safety data in humans from long-term studies are not yet established.

Estrogenic Metabolites and Cumulative Exposure

8-Prenylnaringenin and preparations containing 8-prenylnaringenin have been suggested for use in medicinal and cosmetic applications like hormone replacement or bust enhancement. However, the safety of application is still under considerable debate. Human liver microsomes convert 8-prenylnaringenin to 12 metabolites, with two major ones being estrogenic in vitro themselves. These results represent an important piece of information towards the discussion of safety of use of preparations containing 8-prenylnaringenin.

Breast Cancer Risk

In competitive estrogen receptor (ER) ligand binding assays, 8-PN displayed a high relative binding affinity for both ERs with a preference for ERα and had the strongest mitotic effect on MCF-7 cells among the test substances. Given its potent ERα agonism and the established role of ERα in promoting proliferation of estrogen-responsive breast tissue, all treatments need careful monitoring in terms of both safety and efficacy, not least because other (non-estrogenic) bioactivities of 8-PN and associated hop-derived compounds need to be considered.

Dose-Concentration Limitations

8-PN has proven to be one of the most potent phytoestrogens in vitro known to date, and in the past 20 years, research has unveiled new effects triggered by it in biological systems. However, the majority of 8-PN effects require such high concentrations that they cannot be reached by normal dietary exposure, only pharmacologically; thus, adverse impacts may also emerge. 8-PN can be detected in beer, but the levels are low and should not pose any cause for concern.

Inter-Individual Variability in Conversion from Isoxanthohumol

8-PN can be produced from its precursor, xanthohumol, by the intestinal microbial community of some, but not all, humans in large quantities, meaning that two individuals consuming equivalent amounts of hops or hop extract may achieve substantially different serum levels of 8-PN depending on their gut microbiome composition. This has implications both for predicting therapeutic effect and for assessing estrogenic exposure risk.

Regulatory and Classification Status

Current legislation prevents hop from being classified as a herbal medicine, because there is insufficient evidence for its medicinal use over the required period of time. Hop extract preparations are currently sold as supplements, which makes control of the doses used difficult and thus increases the occurrence of uncontrolled self-treatment.

References

• Milligan SR et al. (1999). Identification of a potent phytoestrogen in hops (Humulus lupulus L.) and beer. Journal of Clinical Endocrinology & Metabolism. PubMed.
• Štulíková K et al. (2018). Therapeutic Perspectives of 8-Prenylnaringenin, a Potent Phytoestrogen from Hops. Molecules 23(3):660. PMC.
• The Potent Phytoestrogen 8-Prenylnaringenin: A Friend or a Foe? International Journal of Molecular Sciences (2022). PMC.
• Flavonoids as Phytoestrogenic Components of Hops and Beer. PMC (2020).
• Bowe J et al. (2006). The hop phytoestrogen, 8-prenylnaringenin, reverses the ovariectomy-induced rise in skin temperature in an animal model of menopausal hot flushes. Journal of Endocrinology 191(2):399–405. PMC.
• Overk CR et al. (2007). The pharmacognosy of Humulus lupulus L. (hops) with an emphasis on estrogenic properties. Phytomedicine. PMC.
• Heyerick A et al. (2006). A first prospective, randomized, double-blind, placebo-controlled study on the use of a standardized hop extract to alleviate menopausal discomforts. Maturitas 54(2):164–175. PubMed.
• Erkkola R et al. (2010). A randomized, double-blind, placebo-controlled, cross-over pilot study on the use of a standardized hop extract to alleviate menopausal discomforts. Phytomedicine 17(6):389–396. PubMed.
• Combination of Soy Isoflavones, 8-Prenylnaringenin and Melatonin Improves Hot Flashes and Health-Related Quality of Life Outcomes in Postmenopausal Women: Flavie Study. PMC (2023).
• Lecomte M et al. (2023). Effect of a Hop Extract Standardized in 8-Prenylnaringenin on Bone Health and Gut Microbiome in Postmenopausal Women with Osteopenia. Nutrients 15(12):2688. PMC.
• Schaefer O et al. (2006). Tissue specificity of 8-prenylnaringenin: protection from ovariectomy induced bone loss with minimal trophic effects on the uterus. Journal of Steroid Biochemistry and Molecular Biology. PubMed.
• Effects and mechanisms of 8-prenylnaringenin on osteoblast MC3T3-E1 and osteoclast-like cells RAW264.7. PMC (2014).
• Effects of 8-Prenylnaringenin and Whole-Body Vibration Therapy on a Rat Model of Osteopenia. PMC (2016).
• Two major metabolites of 8-prenylnaringenin are estrogenic in vitro. Journal of Steroid Biochemistry and Molecular Biology. PubMed (2004).
• Brunelli E et al. (2007). 8-Prenylnaringenin inhibits estrogen receptor-α mediated cell growth and induces apoptosis in MCF-7 breast cancer cells. Journal of Steroid Biochemistry and Molecular Biology. ScienceDirect.
• Schaefer O et al. (2003). 8-Prenyl naringenin is a potent ERα selective phytoestrogen present in hops and beer. Journal of Steroid Biochemistry and Molecular Biology. ScienceDirect.
• Isoxanthohumol and Its Derivatives: Antioxidant Activity and Effects on the Gut Microbiota. Molecules (2026). MDPI.
• Management of menopausal hot flushes. Recommendations from the Spanish Menopause Society. PMC (2025).
• 8-Prenylnaringenin. Wikipedia.
• Health Effects of 8-Prenylnaringenin. Encyclopedia MDPI.