Kaempferol

Kaempferol: A Comprehensive Reference

1. Identity, Chemical Profile, and Natural Sources

1.1 Chemical Identity

Kaempferol (3,5,7-trihydroxy-2-(4-hydroxyphenyl)-4H-1-benzopyran-4-one) is a flavonoid found in many edible plants. It has the molecular formula C₁₅H₁₀O₆, with a relative molecular weight of 286.23, and its chemical name is 3,5,7,4′-tetrahydroxyflavone. It is a natural flavonol — a type of flavonoid — found in a variety of plants and plant-derived foods, including kale, beans, tea, spinach, and broccoli. It is a pure yellow crystalline powder with a melting point of 276–278°C, soluble in hot ethanol, ether alkaline, and slightly soluble in water, possessing hydrophobic properties due to its diphenylpropane structure.

Kaempferol is named in honor of Engelbert Kaempfer, a German doctor, naturalist, and historian who lived during the 17th century and made a significant contribution to transporting medical knowledge from Japan to the West. As a chemical compound, it was discovered in Camellia sinensis (the tea tree).

Kaempferol is common in Pteridophyta, Pinophyta, and Angiospermae. Within Pteridophyta and Pinophyta, kaempferol has been found in diverse families, and it has also been identified in Dicotyledons and Monocotyledons of Angiosperms. Like most flavonoids, kaempferol often exists in various natural plants, fruits, and vegetables in different glycoside forms.

1.2 Botanical and Dietary Sources

Kaempferol is found in many edible plants, including tea, broccoli, cabbage, kale, beans, endive, leek, tomato, strawberries, and grapes. It is also present in plants or botanical products commonly used in traditional medicine, including Ginkgo biloba, Tilia spp., Equisetum spp., Moringa oleifera, Sophora japonica, and propolis.

Kaempferol naturally occurs in tea, as well as numerous common vegetables and fruits including beans, broccoli, cabbage, gooseberries, grapes, kale, strawberries, tomatoes, citrus fruits, Brussels sprouts, apples, and grapefruit. It can be isolated from black, green, and maté herb teas, as well as from numerous common vegetables and fruits.

1.3 Common Forms and Preparations

Like most flavonoids, kaempferol often exists in nature in different glycoside forms. An aglycone produced by hydrolysis of an acidic substance can improve the total extraction rate of kaempferol. In addition, kaempferol, in the form of glycosides, can directly enter the bloodstream and exhibit various biological activities within the human body.

Notable glycoside forms in which kaempferol is commonly encountered include:

• Astragalin (kaempferol-3-glucoside) — a principal form in many foods and herbs
• Tiliroside (kaempferol-3-glucoside-6″-p-coumaroyl) — found in several medicinal plants
• Kaempferitrin (kaempferol-3,7-dirhamnoside) — present in plants such as Justicia spicigera
• Robinin (kaempferol-3-robinobioside-7-rhamnoside) — from Robinia pseudoacacia

These key glycoside derivatives include astragalin, tiliroside, kaempferitrin, and robinin.

As a dietary supplement, kaempferol is commercially available as a standardized extract in capsule and tablet form, typically derived from plant sources such as horseradish leaves (Armoracia rusticana) or other kaempferol-rich botanicals. In research settings, kaempferol has been studied for its ability to enhance hypoxia-induced HIF-1α degradation and increase mitochondrial complex IV activity, thereby stimulating aerobic respiration and increasing ATP content in vitro and in vivo.

2. Traditional and Historical Use

Many of the kaempferol-containing plants are used in traditional systems all over the world for centuries to treat numerous conditions. A number of plants that contain kaempferol compounds are included in many traditional medical systems around the world, and their traditional applications frequently correspond with their current effects under research.

Though limited information is available regarding the cultural significance and ethnobotanical knowledge specific to kaempferol itself, it has a well-documented history of use in Traditional Chinese Medicine (TCM). In China, safflower flowers have been integral to TCM for an extended period, with kaempferol being one of the predominant flavonoid compounds found in safflower flowers.

In Spain, plants belonging to the Mercurialis genus have a longstanding tradition of use in traditional Spanish medicine, with kaempferol being recognized for its anti-inflammatory properties among other pharmacological activities.

Kaempferol occurs in many traditional medical herbs, including Kaempferia rotunda L., Hedyotis diffusa Willd., and Hypericum perforatum (St. John's Wort).

The scientific journey of kaempferol began in the early 1900s when it was first isolated from the tea plant and named after the German botanist Engelbert Kaempfer. It took decades before nutritionists and phytochemists recognized its broad occurrence across fruits and vegetables. Mid-century research identified its antioxidant capacity, and by the 1990s, studies in cell cultures and animals showed anti-inflammatory and cancer-modulating potential.

Herbal medicine is still regarded as an integral part of Traditional Chinese Medicine and continues to be relevant in all parts of the world. Kaempferol-containing plants have been employed across Ayurvedic, European folk, and East Asian herbal traditions — generally prepared as decoctions, infusions (teas), poultices, or whole-food preparations — for purposes including supporting respiratory health, reducing swelling and inflammation, and as general tonics.

3. Key Constituents, Glycosides, and Biosynthesis

The biosynthesis of kaempferol proceeds under catalysis by chalcone synthase, where kaempferol is synthesized by 4-coumaroyl-CoA condensation with tripropionyl-CoA to produce naringenin chalcone. As a secondary metabolite, it belongs to the flavonol subclass of flavonoids, defined by a 3-hydroxyflavone backbone.

The antioxidant activity of kaempferol is attributed in part to the presence of hydroxyl groups within its molecular structure, particularly the one located at the C-3 position. This phenolic hydroxyl configuration underlies its radical-scavenging capacity and its ability to chelate metal ions.

The bioavailability and bioactivity of kaempferol are significantly impacted by the types and attachments of saccharides within the glycosides. The highly polar nature of glycosides affects their absorption, while the intermediate polarity of aglycones facilitates it. Some glycosides require prior hydrolysis to be absorbed, whereas others can be absorbed without this process. In the small intestine, kaempferol is primarily absorbed due to the lipophilicity of its aglycone form, which enables passive diffusion.

4. Pharmacokinetics: Absorption, Metabolism, and Bioavailability

4.1 Absorption

Kaempferol, from a relatively low dose (9 mg), was absorbed from endive with a mean maximum plasma concentration of 0.1 μM, at a time of 5.8 h, indicating absorption from the distal section of the small intestine and/or the colon. Although a 7.5-fold interindividual variation between the highest and lowest maximum plasma concentration was observed, most individuals showed remarkably consistent pharmacokinetic profiles.

An average of 1.9% of the kaempferol dose was excreted in 24 hours. Most subjects also showed an early absorption peak, probably corresponding to kaempferol-3-glucoside, present at a level of 14% in the endive.

4.2 Oral Bioavailability

The oral bioavailability of kaempferol (in rat studies) was poor at approximately 2%. Analysis of portal plasma after oral administration revealed low to moderate absorption. This low bioavailability is attributed in part to extensive first-pass metabolism. The low oral bioavailability of kaempferol is attributed in part to extensive first-pass metabolism by glucuronidation and other metabolic pathways in the gut and in the liver.

After intravenous administration in rats, the plasma concentration-time profiles were consistent with high clearance (approximately 3 L/hr/kg) and large volumes of distribution (8–12 L/hr/kg). The disposition was characterized by a terminal half-life value of 3–4 hours. After oral administration, plasma concentration-time profiles demonstrated fairly rapid absorption (T_max approximately 1–2 hours).

4.3 Metabolism and Circulating Forms

The absorbed kaempferol is rapidly metabolized in the liver and circulates as methyl, glucuronide, and sulfate metabolites. Based on the values of the kinetic constants, the propensity for UDPGA-dependent conjugation compared with NADPH-dependent oxidative metabolism was higher for both hepatic and small intestinal microsomes.

Studies evaluating the bioavailability of food-derived kaempferol conjugates are limited. Existing evidence supporting biological activity has largely been derived from in vitro and animal studies, with limited human clinical data describing absorption, metabolism, and excretion. A multi-site interventional study (NCT07322406) is currently underway to generate comprehensive human pharmacokinetic data. Prior small human studies suggest tolerability but have not provided comprehensive pharmacokinetic characterization or integrated molecular profiling.

5. Mechanisms of Action

5.1 Antioxidant Activity

Kaempferol's mechanism of action appears to be multifaceted, and multiple studies have demonstrated its ability to considerably impede the development of various inflammatory processes by suppressing reactive oxygen species (ROS) generation and exhibiting high anti-oxidative properties. Kaempferol can promote the expression of heme oxygenase-1 (HO-1), inhibit the production of nitric oxide and inducible nitric oxide synthase (iNOS), and reduce the damage of lipopolysaccharide on RAW264.7 macrophages.

5.2 Anti-inflammatory Pathways

Kaempferol inhibits the expression of pro-inflammatory cytokines IL-1β and TNF-α, and disrupts the translocation of NF-κB into the nucleus, thereby hindering the production of inflammatory proteins. The substance also reduces the induction of pro-inflammatory enzymes, including cyclooxygenase-2 (COX-2), phospholipase A2 (PLA2), and inducible nitric oxide synthase (iNOS), which prevent the production of inflammatory mediators of arachidonic acid such as prostaglandins.

Kaempferol has notable anti-inflammatory effects, including regulating the expression of inflammation-related genes and the activity of pro-inflammatory enzymes, and inhibiting the expression of matrix metalloproteinases, adhesion molecules, and transcription factors.

5.3 Nrf2/HO-1 Signaling

Nrf2 is a transcription factor implicated in mediating protection against electrophiles and oxidants and enhances cell survival in many tissues. Nrf2 binds to antioxidant response elements (AREs) and stimulates transcription of antioxidant proteins, which are associated with scavenging ROS and glutathione (GSH) biosynthesis and regeneration. Kaempferol activates this pathway as a key component of its cytoprotective action.

5.4 Apoptosis Modulation in Cancer Cells

At the molecular level, kaempferol has been reported to modulate a number of key elements in cellular signal transduction pathways linked to apoptosis, angiogenesis, inflammation, and metastasis. In terms of its anticancer potential, kaempferol acts through diverse pathways, inducing apoptosis, arresting the cell cycle at the G2/M phase, suppressing epithelial–mesenchymal transition (EMT)-related markers, and affecting the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling pathways.

Besides exerting anti-tumorigenic, antiproliferative, and apoptotic effects against cancer cells, kaempferol also showed protective activity towards healthy, non-cancerous cells.

5.5 Neuroprotective Mechanisms

Kaempferol exhibits a versatile neuroprotective effect by modulating various proinflammatory signaling pathways, including NF-κB, p38MAPK, AKT, and the β-catenin cascade. Additionally, it hinders the formation and aggregation of beta-amyloid protein and regulates brain-derived neurotrophic factors.

5.6 Antidiabetic Mechanisms

Kaempferol's antidiabetic mechanisms operate from three directions: it regulates lipid metabolism and improves insulin resistance to reduce lipotoxicity; it improves insulin signaling and restores the balance between glucose utilization and production, thereby improving glucose toxicity; and it restores the imbalance in autophagy–apoptosis to protect β cells. Therefore, the antidiabetic mechanisms of kaempferol comprehensively prevent the progression of "obesity–insulin resistance–β-cell apoptosis–diabetes–diabetic complications."

5.7 Hepatoprotective Mechanisms

Kaempferol activates the SIRT1/AMPK signalling pathway, improves mitochondrial function, inhibits proinflammatory cytokine production via TLR4/NF-κB suppression, and attenuates hepatic stellate cell activation by modulating the TGF-β/Smad pathway. In addition, kaempferol regulates the composition of the gut microbiota, improving bile acid metabolism and alleviating steatosis and fibrosis.

6. Scientific Evidence by Area of Use

6.1 Cancer — Preclinical and Epidemiological Evidence

Epidemiological studies have shown an inverse relationship between kaempferol intake and cancer. Kaempferol may help by augmenting the body's antioxidant defense against free radicals, which promote the development of cancer.

A PRISMA-compliant systematic review of in vitro studies examining kaempferol's anticancer potential included 64 studies. In vitro experiments demonstrated that kaempferol (KMP) exerts antitumor effects by controlling tumor cell cycle progression, proliferation, apoptosis, migration, and invasion, as well as by inhibiting angiogenesis. KMP was also able to inhibit important markers that regulate epithelial–mesenchymal transition and enhanced the sensitivity of cancer cells to traditional drugs used in chemotherapy, including cisplatin and 5-fluorouracil.

In vitro experiments have indicated that kaempferol can inhibit the proliferation of malignant tumor cells such as breast, colon, lung, bladder, and liver cancers.

Ovarian cancer: An epidemiological study has shown that kaempferol consumption is associated with a linear decline in ovarian cancer risk.

Prostate and bladder cancer: A higher dietary intake of flavonols was associated with a lower risk of both bladder and prostate cancer in epidemiological studies. A total of 21 pre-clinical articles on bladder or prostate cancer reporting on kaempferol were found, while more limited evidence was available from animal models and epidemiological studies or clinical trials. In one preclinical study, kaempferol at concentrations of 5, 10 and 15 μM yielded a reduction in androgen-dependent LNCaP prostate cancer cell growth of 33%, 60% and nearly 100%, respectively.

Gastric cancer: In 2010, kaempferol revealed dosage- and time-dependent inhibitory effects on MGC-803 gastric cancer cells, causing apoptosis and G2/M phase arrest. Song et al. found that kaempferol promoted apoptosis and G2/M phase cell cycle arrest in gastric cancer cell lines, including MKN-28 and SGC-7901, but it had no impact on standard gastric epithelial cell lines.

Overall evidence strength — cancer: The body of cancer-related evidence for kaempferol is substantial at the in vitro and animal model levels. Epidemiological associations are present but do not establish causality. Controlled human clinical trials specifically evaluating kaempferol as an isolated anticancer agent are essentially absent. Despite promising findings in preclinical and clinical research, further research is needed to confirm its efficacy and understand the mechanisms of action, and to fully explore the potential of kaempferol in different cancers.

6.2 Cardiovascular Health

Some epidemiological studies have found a positive association between the consumption of foods containing kaempferol and a reduced risk of developing several disorders such as cancer and cardiovascular diseases. The potential cardioprotective effects of kaempferol in in vitro and animal studies have been attributed to its anti-inflammatory activities.

Epidemiological studies have investigated associations between intakes of dietary flavonoids, specifically kaempferol, and cardiovascular health, but clinical trials on the cardioprotective benefits of kaempferol are limited.

Some epidemiological researchers have discovered a link between intake of foods high in flavonoids and lower threat of emerging cardiovascular disease and cancer, and in vitro and in vivo studies have displayed probable pathways through which flavonols may protect against cardiovascular diseases and cancer.

Overall evidence strength — cardiovascular: Evidence consists primarily of in vitro mechanistic studies and epidemiological associations at the dietary flavonol level; it cannot be attributed specifically to kaempferol alone. Dedicated human clinical trials are lacking.

6.3 Anti-inflammatory and Rheumatological Effects

Kaempferol exhibits anti-inflammatory properties and has been used to address many acute and chronic inflammation-induced diseases, such as intervertebral disc degeneration and colitis, post-menopausal bone loss, and acute lung injury.

In interleukin-1β-stimulated rat chondrocytes, kaempferol effectively reduced the activity of iNOS and Cox-2. Kaempferol boasts a longstanding history of traditional use in treating various inflammatory diseases, and pharmacological studies have illustrated its potential to reduce iNOS and Cox-2 expression.

Overall evidence strength — anti-inflammatory: Mechanistic evidence is well-developed in vitro and in animal models. Human clinical evidence specific to kaempferol is sparse.

6.4 Neuroprotection and CNS Diseases

Experimental studies have addressed the isolated action of kaempferol (C₁₅H₁₀O₆) and its derivatives in neurological diseases such as Alzheimer's disease, Parkinson's disease, ischemia stroke, epilepsy, major depressive disorder, anxiety disorders, and glioblastoma.

Kaempferol exhibits a versatile neuroprotective effect by modulating various proinflammatory signaling pathways, including NF-κB, p38MAPK, AKT, and the β-catenin cascade. Additionally, it hinders the formation and aggregation of beta-amyloid protein and regulates brain-derived neurotrophic factors.

In animal studies of cerebral ischemia-reperfusion (I/R) injury, kaempferol improved the arrangement, distribution, and morphological structure of neurons, as well as attenuated cell apoptosis in brain tissue. Kaempferol mitigated oxidative and inflammatory stress via regulating the expression of Nrf2, p-Akt, p-GSK-3β, and p-NF-κB during cerebral I/R, increasing the activity of SOD and GSH, while decreasing the content of MDA in serum and brain tissue.

Overall evidence strength — neuroprotection: Little is known about the cellular and molecular mechanisms underlying kaempferol's actions in the central nervous system at the human clinical level. Evidence remains at the preclinical (in vitro and animal model) stage, with no completed human trials specifically for neurological endpoints.

6.5 Diabetes and Metabolic Disease

Kaempferol regulates lipid metabolism and improves insulin resistance to reduce lipotoxicity. It improves insulin signaling and restores the balance between glucose utilization and production, thereby improving glucose toxicity. Finally, kaempferol restores the imbalance in autophagy–apoptosis to protect β cells.

Chen et al. indicated that kaempferol significantly inhibited inflammatory cytokine expression and high glucose-induced ROS production. Kaempferol exerted protective effects in diabetic cardiomyopathy by suppressing nuclear translocation of NF-κB and activating NF-erythroid 2 p45-related factor-2. In addition, kaempferol may protect β cells from glucose toxicity and mediate anti-apoptotic effects by improving cAMP/protein kinase A and PI3K/Akt signaling pathways.

Overall evidence strength — diabetes: Preclinical data in cell culture and animal models is extensive. According to a recent review, the natural product kaempferol has excellent antidiabetic effects in animal models, but human clinical trials are required to validate these findings in diabetic patients.

6.6 Liver (Hepatoprotective) Effects

Kaempferol is a potent antioxidant with anti-inflammatory effects, which therefore possesses hepatoprotective properties. Previous research has studied the hepatoprotective effect of kaempferol in various hepatotoxicity protocols, including acetaminophen (APAP)-induced hepatotoxicity, alcoholic liver disease (ALD), nonalcoholic fatty liver disease (NAFLD), carbon tetrachloride (CCl₄), hepatocellular carcinoma (HCC), and lipopolysaccharide (LPS)-induced acute liver injury.

In a rat study of CCl₄-induced acute liver damage, oral administration of kaempferol at doses of 5 and 10 mg/kg body weight resulted in the amelioration of CCl₄-induced abnormalities in hepatic histology and serum parameters. Additionally, kaempferol decreased the levels of pro-inflammatory mediators TNF-α and IL-1β, as well as COX-2 and iNOS, and suppressed NF-κB p65 activation, as well as the phosphorylation of Akt and MAPK members.

Overall evidence strength — hepatoprotection: Evidence is largely from animal models and in vitro studies. No controlled human clinical trials specifically evaluating kaempferol's hepatoprotective effects have been published to date.

6.7 Bone Health (Osteoprotective Effects)

Kaempferol is referred to as a nutraceutical due to its various health benefits previously proven scientifically, which include cardioprotective, neuroprotective, anxiolytic, analgesic, anti-allergic, anti-platelet aggregation, anti-cancer, anti-microbial, anti-obesity, anti-hyperglycemic, anti-hypertensive, anti-hyperlipidemic, anti-aging, anti-oxidative, anti-inflammatory, and anti-osteoporotic effects.

Kaempferol has been used in preclinical research to address post-menopausal bone loss, and kaempferol is also used to treat numerous acute or chronic diseases, including intervertebral disc degeneration and post-menopausal bone loss.

Overall evidence strength — bone: In vitro and animal data support osteogenic and bone-protective mechanisms. Human trials are not yet available.

6.8 Antimicrobial Effects

Apart from their anticarcinogenic and anti-inflammatory effects, kaempferol and its associated compounds also exhibit antibacterial, antifungal, and antiprotozoal activities. The development of drugs and treatment schemes based on these compounds is becoming increasingly important in the face of emerging resistance of numerous pathogens as well as complex molecular interactions between various drug therapies.

Overall evidence strength — antimicrobial: Evidence is confined to in vitro studies and some animal model data. Clinical validation in humans has not been conducted for isolated kaempferol.

6.9 Obesity

Several papers have reported the positive effects of dietary kaempferol in reducing the risk of chronic diseases, such as cancer, liver injury, obesity, and diabetes. In vitro research has specifically examined kaempferol's effects on adipogenesis and lipolysis in 3T3-L1 cells (a standard pre-adipocyte cell model), suggesting anti-obesity mechanisms at the cellular level.

Overall evidence strength — obesity: Preliminary; primarily cell-based and animal model evidence. No human trials specifically targeting obesity with isolated kaempferol have been reported.

7. Body Systems Associated with Kaempferol

• Immune and inflammatory system: Inhibition of NF-κB, COX-2, iNOS, TNF-α, IL-1β, and IL-6; activation of Nrf2/HO-1 antioxidant signaling.
• Cardiovascular system: Endothelial protection, anti-atherosclerotic activity in animal models, epidemiological associations with reduced CVD risk.
• Central nervous system: Modulation of beta-amyloid aggregation, BDNF regulation, neuroprotection against ischemia-reperfusion injury.
• Endocrine/metabolic system: Insulin sensitization, β-cell protection, lipid metabolism regulation.
• Hepatic system: Protection against drug-, alcohol-, and lipid-induced hepatotoxicity via SIRT1/AMPK and TGF-β/Smad pathways.
• Skeletal system: Osteogenic support, protection against post-menopausal bone loss in preclinical models.
• Gastrointestinal system: Modulation of gut microbiota composition, anti-colitis effects in animal models.
• Oncology: Cell cycle arrest, pro-apoptotic activity in cancer cell lines, anti-angiogenic effects.

Due to its anti-inflammatory properties, kaempferol may be used to treat numerous acute and chronic inflammation-induced diseases, including intervertebral disc degeneration and colitis, as well as post-menopausal bone loss and acute lung injury. In addition, it has beneficial effects against cancer, liver injury, obesity, and diabetes, inhibits vascular endothelial inflammation, protects the cranial nerve and heart function, and may be used for treating fibroproliferative disorders, including hypertrophic scar.

8. Dosage Forms and Doses Reported in Studies

In a randomized, placebo-controlled human safety trial, the kaempferol (KMP) group received a capsule containing 50 mg of KMP aglycone daily — a dose approximately five times higher than the estimated human dietary intake — for 4 weeks.

In animal (rat) hepatoprotection studies, oral administration of kaempferol at doses of 5 and 10 mg/kg body weight resulted in the amelioration of CCl₄-induced abnormalities in hepatic histology and serum parameters.

In animal pharmacokinetic studies, male Sprague-Dawley rats were administered kaempferol intravenously at 10 and 25 mg/kg, or orally at 100 and 250 mg/kg.

In the human absorption pharmacokinetic study from endive, the objective was to determine the absorption, excretion, and metabolism of kaempferol in humans over 24 hours in a group of four healthy males and four healthy females, and kaempferol from a relatively low dose of 9 mg was absorbed with a mean maximum plasma concentration of 0.1 μM at 5.8 hours.

In a crossover study, De Vries et al. examined the digestion and absorption of kaempferol from black tea in participants (n = 15) who consumed 27 mg of kaempferol from black tea for three days.

Kaempferol supplement products are commonly formulated as oral capsules or tablets, with doses typically ranging from 50 mg to several hundred mg, though these commercial doses are not yet validated by robust clinical trial data for efficacy endpoints. A multi-site interventional study is designed to generate human data to inform regulatory and translational planning for kaempferol.

9. Safety, Toxicity, and Drug Interactions

9.1 Clinical Safety in Humans

The general toxicity parameters were evaluated by examining hematological and blood biochemical parameters, general urinalysis, qualitative urine tests, and adverse events. No clinical changes were observed in anthropometric and blood pressure measurements or blood and urine parameters in the kaempferol group compared to those in the placebo group. Furthermore, no adverse events owing to kaempferol aglycone administration occurred. The study results revealed that the consumption of 50 mg kaempferol aglycone daily for 4 weeks is safe in healthy adults.

9.2 Genotoxicity Concerns (In Vitro)

It should be noted that kaempferol exhibits a range of biological activities, some of which, depending on the circumstances, may be beneficial or detrimental. Kaempferol has been reported to have mutagenic and genotoxic properties in experiments on Drosophila melanogaster. In vitro, kaempferol may induce chromosomal aberrations in V79 Chinese hamster cells. This is thought to involve the biotransformation of kaempferol to quercetin by cytochromes P450 in the presence of metabolic activation systems.

Kaempferol has been shown to be genotoxic to V79 cells in the absence of external metabolizing systems. The presence of an external metabolizing system, such as rat liver homogenates (S9 mix), leads to an increase in its genotoxicity, which is attributed to its biotransformation to the more genotoxic flavonoid quercetin, via the cytochrome P450 (CYP) mono-oxygenase system. These findings are from in vitro studies and their relevance to human dietary exposures is uncertain.

9.3 Pro-oxidant Activity

With its interaction with free radical generation in an oxidative stress environment, kaempferol tends to have pro-oxidant activity and produce genotoxic effects. Various antioxidants and pro-oxidant enzymes regulate these pro-oxidant mechanisms. This context-dependent dual activity (antioxidant vs. pro-oxidant) is a pharmacologically recognized characteristic of polyphenols and is considered relevant primarily under supraphysiological concentrations.

9.4 Drug Interactions — CYP450 Enzymes

In vitro studies of kaempferitrin (a kaempferol glycoside) with CYP isoforms indicate that it has the potential to cause pharmacokinetic drug interactions with other co-administered drugs metabolized by CYP1A2, 3A4, and 2C9.

Epimedium (a kaempferol-containing botanical) inhibited CYP3A4 activity in a dose-dependent manner. Dexamethasone enhanced the expression of CYP3A4 mRNA, while epimedium inhibited the expression of CYP3A4 mRNA and further suppressed dexamethasone enhancement of CYP3A4 mRNA expression in HepG2 cells. These findings suggest that kaempferol-containing preparations may potentially alter the metabolism of drugs processed by this major enzyme pathway, including certain corticosteroids, statins, and immunosuppressants.

It is recommended, based on in vitro data, that kaempferol glycosides should not be used with other drugs metabolized by CYP1A2, 3A4, and 2C9, and that further clinical studies are needed to evaluate the significance of this interaction.

9.5 Additional Safety Considerations

The safety and toxic profile of kaempferol aglycone has been evaluated in vitro and in vivo; however, in human research, although there are reports of studies using kaempferol glycosides and conjugates, to date there are no reports of clinical trials evaluating the long-term safety of kaempferol aglycone beyond the 4-week period studied.

It has been reported that kaempferol may result in a multitude of adverse consequences under specific experimental conditions, though the clinical significance of many in vitro findings at dietary exposure levels remains to be determined. The overall preclinical and short-term human safety profile appears favorable at moderate doses, but long-term human safety data are lacking.

10. Research Landscape and Evidence Gaps

By February 26, 2024, 11,214 publications on kaempferol were identified in the Web of Science Core Collection database, comprising 10,746 original articles (96%) and 468 review articles (4%). This large body of literature is dominated by preclinical work.

Limited data is available on comparative studies of drugs and kaempferol being used as treatment in pre-clinical or clinical trials. Existing evidence supporting biological activity has largely been derived from in vitro and animal studies, with limited human clinical data. The major unresolved questions include optimal dosing and dosing interval in humans, formulation strategies to improve bioavailability, long-term safety at supplemental doses, and whether in vitro and animal findings translate to meaningful clinical outcomes in specific disease populations.

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