Ellagic Acid: A Comprehensive Reference
1. Identity and Chemical Characterization
Names and Classification
Ellagic acid (EA) was first discovered in 1831 by the French chemist and pharmacist Henri Braconnot, who named it acide ellagique — a reversal of the word galle, the French word for oak gall, from which it can be obtained. The International Union of Pure and Applied Chemistry (IUPAC) name of ellagic acid is 2,3,7,8-tetrahydroxy-chromeno[5,4,3-cde]chromene-5,10-dione. It has a chemical formula of C14H6O8 and from the physicochemical perspective, it exists in the form of cream-colored needles or yellow powder with a melting point greater than 360°C.
EA is known as a naturally occurring bioactive and pharmacologically active polyphenolic compound that is abundant in many taxonomically diverse plant groups, mainly among eudicotyledons. Structurally, EA constitutes a dilactone of hexahydroxydiphenic acid (HHDP), which can be considered a dimeric gallic acid derivative. The molecular structure resembles that of two gallic acid molecules assembled "head to tail" and bound together by a C–C bond and two lactone links (cyclic carboxylic esters).
Historical Isolation
Ellagic acid was first discovered by chemist Henri Braconnot in 1831. Maximilian Nierenstein prepared the substance from algarobilla, dividivi, oak bark, pomegranate, myrabolams, and valonea in 1905. He also suggested its formation from galloyl-glycine by Penicillium in 1915. Julius Löwe was the first person to synthesize ellagic acid by heating gallic acid with arsenic acid or silver oxide.
Natural Forms in Plants
Ellagic acid is a naturally occurring polyphenolic compound detected in free form or linked to polyols or sugars, constituting hydrolyzable tannins or ellagitannins in distinct fruits, nuts, and herbs. Plants can embody EA in three distinct forms: free EA, ellagic acid glycosides, and polymeric ellagitannins, even if in varying quantities. EA is predominantly detected as ester-linked to sugars in the composition of hydrolyzable tannins called ellagitannins. Plants produce ellagic acid from hydrolysis of tannins such as ellagitannin and geraniin.
2. Natural Sources and Botanical Distribution
The highest levels of ellagic acid are found in raw chestnuts, walnuts, pecans, cranberries, raspberries, strawberries, and grapes, as well as distilled beverages. It is also found in peaches and pomegranates. EA is primarily plentiful in berries of the family Rosaceae, such as raspberry, cherry, and strawberry.
Terminalia chebula, Quercus robur, Castanea (chestnut), pomegranate, black raspberries, strawberries, walnuts, and almonds are some of the plants, fruits, and nuts reported to possess high concentrations of ellagitannins. Ellagic acid is also found in oak species such as the North American white oak (Quercus alba) and European red oak (Quercus robur). The macrophyte Myriophyllum spicatum produces ellagic acid. Ellagic acid can also be found in the medicinal mushroom Phellinus linteus.
Ellagic acid has been detected in many studies with fruits, nuts, and berries, in which the total ellagic acid concentration was measured by analyzing the ellagic acid concentration of extracts after acid hydrolysis. In raspberries, free ellagic acid comprises only a minor part of the total ellagic acid pool, and ellagitannins are the primary source of ellagic acid released by acid hydrolysis.
Estimated Dietary Intake
In the UK, it has been estimated that EA intake is about 5 mg/day; however, for some individuals, it may be 100 mg/day if pomegranate, berries, or walnuts are regularly eaten. In the US, the mean intake is 5–5.9 mg/day, while the consuming recommended levels in men and women are estimated to be 17.9 and 27.6 mg/day, respectively. The intake of phytonutrients, including EA, is low among adults who consume less than the daily-recommended amount of fruit and vegetables.
3. Traditional and Historical Uses
Many species of medicinal plants used in traditional medicine around the world, including Traditional Chinese Medicine and Ayurveda, have been found to contain EA and ellagitannins. As a compound rather than a plant, ellagic acid itself was not identified or named in pre-modern traditions; however, the EA-rich plant sources central to those traditions are well documented.
Persian and Mediterranean diets prominently featured pomegranate molasses and seeds. Native American practices included using raspberry leaves for teas. Cuisine of Northern India incorporated walnut chutneys, particularly in Kashmir.
Punica granatum (pomegranate) is used as herbal medicine and abundantly grows in the Middle East. The main pharmacological compounds of P. granatum are flavonoid and phenolic compounds (including ellagic acid), which are known as potent antioxidants. Different parts of the pomegranate, including rind, peel, and fruit, were applied across various traditional cultures for their perceived beneficial effects on health.
Due to its wide range of biological effects, edible plants containing this phytochemical and its hydrolyzable derivatives (mainly ellagitannins) are a valuable source of EA for humans and belong to functional foods that promote health and may reduce the risk of disease.
4. Key Constituents, Metabolites, and Active Compounds
Ellagitannins as Precursors
EA is a dilactone of hexahydroxydiphenic acid (HHDP), a dimeric gallic acid derivative, produced mainly by hydrolysis of ellagitannins — a widely distributed group of secondary metabolites. Ellagitannins are the dominant polyphenols in pomegranate, with punicalagin being the most abundant representative. Once exposed to water, punicalagin is rapidly hydrolyzed, releasing ellagic acid.
Urolithins: The Bioavailable Gut Metabolites
Since tannins are not bioavailable, they were historically neglected in nutrition science and even considered antinutrients. However, this view changed dramatically once it was recognized that ellagic acid, released from ellagitannins in the gastrointestinal system, is further metabolized by colonic microbiota to bioavailable compounds known as urolithins. Urolithins (3,4-benzocoumarin derivatives) have emerged as novel natural bioactive compounds and are now the focus of extensive investigations.
Ellagic acid has low bioavailability, with 90% remaining unabsorbed from the intestines until metabolized by microflora to the more bioavailable urolithins. These compounds are produced by gut microbes in the colon after consumption of ellagitannin-rich food, and their production is highly associated with individual gut microbiota composition (urolithin metabotypes). The highly bioavailable urolithins are absorbed mainly in the colonic mucosa, where they are subjected to phase II metabolism, resulting in the formation of glucuronic and sulphate conjugates. These conjugates reach plasma and systemic tissues within three to four days and exert their bioactivity.
The low bioavailability of antioxidant ellagitannins and ellagic acid is a significant limitation. The main ellagitannin metabolites circulating in plasma are ellagic acid microbiota metabolites known as urolithins, and they have lost their free-radical scavenging activity. They are present in plasma as glucuronate or sulfate conjugates, at concentrations in the nanomolar range.
One study reported that human subjects taking 180 mL of pomegranate juice (25 mg of ellagic acid, 318 mg of ellagitannins) had 31.9 ng/mL of ellagic acid in plasma one hour post-ingestion, which was eliminated by four hours. There is huge variability in microbial metabolism of EA between individuals, depending on differences in gut microbial ecology.
5. Mechanisms of Action
Antioxidant Activity
The high antioxidant activity of ellagic acid is based both on direct free radical scavenging, the inhibition of lipid peroxidation, as well as the enhancement of antioxidant enzyme activities such as superoxide dismutase, catalase, and glutathione peroxidase.
Nrf2/ARE Pathway Activation
In addition to its anti-inflammatory effects, ellagic acid modulates the antioxidant response by promoting nuclear factor erythroid 2-related factor 2 (Nrf2) activation and upregulating heme oxygenase-1 (HO-1) expression, ultimately protecting tissues from oxidative damage. Ellagic acid can inhibit Keap1 to accumulate Nrf2 in the nucleus, and act on the antioxidant response element (ARE) to produce target proteins, which in turn may alleviate the impact of oxidative stress on neuronal cells.
NF-κB Pathway Inhibition
EA exerts effects through multiple mechanisms, including scavenging reactive oxygen species (ROS) and enhancing endogenous antioxidant defenses (e.g., by activating Nrf2/ARE), modulating inflammatory signaling pathways (e.g., inhibiting NF-κB, TNF-α, and IL-6), and regulating apoptosis (e.g., downregulating the Bax/Bcl-2 ratio) and fibrosis (e.g., inhibiting TGF-β/Smad signaling).
Cell Cycle and Apoptosis Modulation
The ameliorative effects of EA proceed via several mechanisms including: (i) activation of the antioxidant response through the Nrf2/HO-1 signaling pathway; (ii) inhibition of pro-inflammatory agents, such as iNOS, COX-2, and cytokines by inhibiting NF-κB; (iii) alteration of several growth factors expression, including TGF-α, vascular endothelial growth factor, and VEGFR; (iv) modulation of several cell survival and cell-cycle genes such as Bcl-2, Bax, caspase-3 and tumor suppressors (p53); and (v) regulation of kinases, like PI3-K and GSK-3β.
Ellagic acid down-regulates insulin-like growth factor IGF-II and activates p53/p21 expression, leading to cell cycle arrest at the G1/S phase and apoptosis. Microarray analysis revealed that EA modulates several genes. Specifically, EA overexpresses genes involved in DNA repair, such as xeroderma pigmentosum group A complementing protein, DNA ligase III, and DNA excision repair protein, by threefold to eightfold.
Cytochrome P450 Modulation
Ellagic acid exerts a dose-dependent impact on the metabolism of chemical carcinogens and drugs by affecting the enzymes involved in xenobiotics activation/detoxification and antioxidant pathways. Certain cytochrome P450 enzymes are inhibited by ellagic acid, preventing other carcinogens from being metabolized into more mutagenic forms.
6. Scientific Evidence by Area of Use
6.1 Antioxidant and Anti-Inflammatory Activity
EA, as a dietary polyphenol, exhibits potent antioxidant and anti-inflammatory activities, demonstrating therapeutic potential across various disease areas. Mechanistically, EA modulates key signalling pathways like NF-κB, MAPK, and Nrf2/ARE, impacting cellular processes such as apoptosis, oxidative stress, and inflammation. The bulk of this evidence derives from in vitro and animal model systems. Human clinical evidence directly attributing these effects to isolated ellagic acid specifically (as opposed to whole fruit or ellagitannin-rich preparations) is limited.
6.2 Oncology and Chemoprevention
Ellagic acid is a naturally occurring polyphenolic compound endowed with strong antioxidant and anticancer properties. The antitumor activity of EA has been mostly attributed to direct antiproliferative and apoptotic effects. Moreover, EA can inhibit tumor cell migration, extracellular matrix invasion, and angiogenesis — all processes crucial for tumor infiltrative behavior and the metastatic process. In addition, EA may increase tumor sensitivity to chemotherapy and radiotherapy.
EA exerts potent preventive and therapeutic effects against several types of cancers, including colon cancer, breast cancer, prostate cancer, skin cancer, esophageal cancer, and osteogenic sarcoma. The cytotoxic and antiproliferative activities of EA against cancer cells do not affect normal cell viability; that is, EA is selectively cytotoxic to carcinoma cells but not to normal cells, based on cell line studies.
In vivo EA administration during 1,2-dimethylhydrazine-induced colon carcinogenesis in rats resulted in a chemopreventive effect through anti-inflammatory properties, exerted by inhibition of NF-κB and subsequent iNOS, COX-2, TNF-α, and IL-6 downregulation. In the same colon cancer model, EA induced apoptosis by preventing PI3K/Akt signalling pathway activation and modulating downstream Bcl-2 family proteins. Bax expression and caspase-3 activation was also observed, leading to higher cytochrome c levels in the cytosol and eventually to cell death.
In a study investigating anti-invasive effects of EA in androgen-independent human (PC-3) and rat (PLS10) prostate cancer cell lines in vitro, non-toxic concentrations of EA significantly inhibited the motility and invasion of cells examined in migration and invasion assays. EA treatment slightly decreased secretion of matrix metalloproteinase (MMP)-2 but not MMP-9 from both cell lines.
Human/Clinical Evidence (Cancer): The EA oral administration as supportive therapy to standard chemotherapy has been evaluated in small clinical studies with colorectal or prostate cancer patients. Pre-clinical studies indicate anticarcinogenic effects against liver, esophageal, prostate, and colorectal cancer cell lines. In an exploratory study of patients with biochemically recurrent prostate cancer, grape skin comprising ellagic acid, quercetin, and resveratrol was reported to be safe and to affect a non-significant increase in prostate-specific antigen doubling time. Further research is needed to assess the anticancer potential of ellagic acid. Overall, the clinical evidence in humans remains preliminary and insufficient to draw conclusions about efficacy.
6.3 Metabolic Syndrome, Diabetes, and Cardiovascular Risk
Several investigations have indicated that ellagic acid could be a potent compound for the treatment of many disorders such as diabetes, hypertension, and hyperlipidemia by various mechanisms, including increasing insulin secretion, insulin receptor substrate protein 1 expression, regulating glucose transporter 4, triglyceride, total cholesterol, LDL, HDL, attenuating TNF-α, IL-6, reactive oxygen species, malondialdehyde, and oxidative stress in related tissues.
Key Clinical Trial: A randomized, double-blind, placebo-controlled clinical trial with 32 volunteers diagnosed with metabolic syndrome evaluated the effect of EA on MetS components, insulin sensitivity, and insulin secretion. Sixteen patients received 500 mg of EA orally twice a day for 12 weeks, and the other 16 received a placebo. After 12 weeks, ellagic acid consumption enhanced insulin sensitivity, decreased insulin secretion, and improved MetS components. It reduced abdominal obesity, blood pressure, fasting glucose, and triglycerides for males and females, with an increase in HDL-c in only male patients.
Limitations and Conflicting Evidence: A systematic review and meta-analysis found that EA significantly reduces glucose, HbA1c, OGTT, HOMA-IR, HOMA-B, BUN, and creatinine in animal models with metabolic abnormalities. In contrast, EA exhibits no significant effects on glucose, insulin, or HOMA-IR in humans. The absence of significant effects in humans highlights the need for high-quality clinical trials to determine its translational potential.
Small clinical studies have shown that ellagic acid may lower cholesterol and decrease lipid peroxidation in patients with metabolic syndrome. One study found that consumption of a drink made with freeze-dried strawberry powder for 4 weeks lowered total cholesterol and LDL levels in obese women with metabolic syndrome. These berry-based studies cannot isolate ellagic acid as the operative agent, making interpretation difficult.
6.4 Hepatoprotective Activity
In a murine model of acute liver injury induced by LPS and D-galactosamine, ellagic acid was found to inhibit NF-κB activation, thereby regulating the inflammatory activities of neutrophils and macrophages at the site of hepatic injury. In addition to its anti-inflammatory effects, ellagic acid also modulated the antioxidant response by promoting Nrf2 activation and upregulating HO-1 expression, ultimately protecting liver tissue from oxidative damage.
Research has indicated that this natural compound may have the potential to prevent or reduce toxicity in the liver by inhibiting NF-κB activation and NO generation, and by enhancing the cellular antioxidant system. Despite promising preclinical efficacy, the clinical applicability of EA is currently limited by its poor bioavailability. This could potentially be overcome by advanced delivery systems or by directly administering its active microbial metabolites, known as urolithins. Human clinical evidence for hepatoprotection specifically from ellagic acid supplementation is not yet established.
6.5 Neuroprotection and Cognitive Function
Ellagic acid, an extraction component of fruits and nuts, presents many pharmacological activities such as anti-inflammation, antioxidation, and neuroprotection. Cell culture studies indicate that EA promoted neuronal survival. The Keap1-Nrf2-ARE pathway can induce cell oxidation resistance and reduce nerve injury to treat neurodegenerative diseases. EA can inhibit Keap1 to accumulate Nrf2 in the nucleus, and act on the ARE to produce target proteins, which in turn may alleviate the impact of oxidative stress on neuronal cells in Parkinson's disease models.
Administration of pomegranate peel extract solution (50 mg/kg) and ellagic acid for 4 weeks improved memory deficit and degenerative changes in an AlCl3-induced rat model of Alzheimer's disease. In in vitro studies on H4 human neuroglioma cells, the effect of amyloid-β (Aβ1-42)-stimulated tau phosphorylation (pTau-181) was significantly attenuated by ellagic acid treatment.
A considerable number of botanicals and enriched foods containing EA are commercially available as nutraceuticals and used to prevent mild cognitive impairment (MCI) due to the excellent neuroprotective capacity of EA. Small clinical studies have shown that ellagic acid may help restore cognitive performance associated with mild age-related decline. Evidence in this domain remains largely preclinical; controlled human trials with isolated ellagic acid as the intervention are sparse.
6.6 Antimicrobial and Antiviral Activity
EA possesses antibacterial, antifungal, antiviral, and anti-inflammatory properties that might be related to its antioxidant effect. In vitro, pomegranate extracts and ellagitannins interact with and inhibit the infectivity of a range of viruses, including SARS-CoV-2. In silico docking studies show that ellagitannins bind to several SARS-CoV-2 and human proteins, including a number of proteases. These findings are entirely preclinical; no human clinical evidence for antimicrobial efficacy of supplemental EA has been established.
6.7 Skin Protection
In humans, oral administration of pomegranate extract enriched with ellagic acid is reported to be beneficial for minimizing ultraviolet-induced skin damage. This observation comes from a small human study using a pomegranate extract (not isolated ellagic acid), so it cannot be attributed solely to EA; the evidence base for this application is preliminary.
6.8 Renal Protection
EA administration protects carbon tetrachloride-induced kidney damage against oxidative stress through its antioxidant protection. Treatment with EA significantly reduced lipid peroxidation and improved glutathione and catalase enzyme activity — findings from animal (rat) models. A meta-analysis found that EA lowers blood urea nitrogen and creatinine in metabolically impaired animals. Human clinical data for renal protection are not available.
7. Body Systems and Health Areas Associated with Ellagic Acid
- Hepatic system: Ellagic acid has numerous pharmacological properties, including antioxidant, anti-inflammatory, apoptosis-mediating, and anti-fibrotic activities, that are studied in the context of liver disease.
- Cardiovascular system: EA has been well documented for its antiallergic, antiatherosclerotic, and cardioprotective properties.
- Nervous system: EA has been documented for neuroprotective properties.
- Metabolic system: EA has been linked to hepatoprotective, cardioprotective, chemopreventive, neuroprotective, gastroprotective, and antidiabetic properties.
- Renal system: EA has also been well documented for nephroprotective properties.
- Immune and oncologic system: Urolithins, the gut metabolites of EA, were shown to be powerful modulators of oxidative stress and agents with potential anti-inflammatory, antiproliferative, and antiaging properties.
- Gut microbiota interaction: EA and urolithins exhibit a spectrum of beneficial biological activities, including antioxidant, anti-inflammatory, and anticancer properties, along with enhancements to intestinal barrier function and modulatory effects on metabolic and cardiovascular systems.
8. Dosage Forms and Dosages Reported in Studies
EA is currently used in the pharmaceutical and cosmetics industries. Ellagic acid has been marketed as a dietary supplement with various claimed benefits against cancer, heart disease, and other diseases.
Common preparation forms in research and commerce include:
- Oral capsules or tablets of purified ellagic acid
- Standardized pomegranate extracts (containing known amounts of ellagitannins and/or free EA)
- Pomegranate juice preparations
- Phospholipid complexes designed to enhance bioavailability
The following dosages are specifically reported in published studies:
- In the metabolic syndrome randomized controlled trial, 16 patients received 500 mg of EA orally twice a day (1,000 mg/day total) for 12 weeks.
- A crossover pharmacokinetic study in 19 healthy male subjects used 500 mg ellagic acid capsules as one arm, compared against a single dose of 8 oz pomegranate juice.
- In a rat study evaluating effects on hepatic drug-metabolizing enzymes, EA was administered at 10 or 30 mg/kg/day intragastrically for 14 consecutive days.
- In most in vivo (animal) studies for treating diabetes, the effective dose of EA was in the range of 50–200 mg/kg/day given orally.
- A pharmacokinetic study in Wistar rats examined an EA-phospholipid complex (equivalent to 80 mg/kg/day of EA) and found serum concentrations from the complex (Cmax = 0.54 μg/mL) were higher than from the equivalent dose of free form EA (Cmax = 0.21 μg/mL).
- A dose-dependent response was observed with pomegranate extract, with the 1,000 mg dose group exhibiting a two-fold increase in the area under the curve for conjugated ellagic acid compared to 250 mg.
- In a rat Alzheimer's disease model, pomegranate peel extract at 50 mg/kg alongside ellagic acid was administered for 4 weeks.
No universally established human therapeutic dose has been confirmed by regulatory bodies. The clinical trial literature primarily reports doses in the range of 500–1,000 mg/day in adults, but the evidence base is insufficiently mature to support standardized dosing recommendations.
9. Safety Considerations and Drug Interactions
General Tolerability
Toxicology data from human and in vivo studies highlight the safety of ellagitannin foods and supplements even at high doses. In the published clinical trial using 500 mg twice daily for 12 weeks, no serious adverse events were reported in the published results. However, the small sample sizes of human trials limit conclusions about long-term or high-dose safety.
Cytochrome P450 Interactions
Ellagic acid inhibits cytochrome P450 2A2, 3A1, 2C11, 2B1, 2B2, and 2C6 enzymes, and may increase the risk of side effects of drugs that are substrates of these enzymes. The clinical relevance of these interactions is not yet known.
In rats, while NQO1, catalase, GPX, and glutathione S-transferase activities were increased significantly at the 30 mg/kg/day dose, CYP1A, 2B, 2C, 2E, and 19 enzyme activities were reduced significantly. CYP2B, 2C6, 2E1, and 19 protein and mRNA levels were substantially decreased by the 30 mg/kg/day dose, but the CYP1A protein and mRNA levels were not changed. CYP3A enzyme activity, protein, and mRNA levels were not altered by either 10 nor 30 mg/kg/day ellagic acid in this animal model. Whether these effects translate to clinically relevant drug interactions in humans at supplement doses requires further investigation.
Bioavailability Limitations as a Safety Modifier
The clinical applicability of EA is currently limited by its poor bioavailability. The extent to which circulating free ellagic acid — versus its urolithin metabolites — is responsible for observed effects in vivo remains actively debated. The bioavailability of ellagic acid has been reported to be very low and the existing studies are controversial.
Individual Variability in Metabolism
The bioavailability of ellagitannins appears to be dependent on the composition of gut microbiota. Differences exist in the metabolism of ellagitannins and EA depending on the variability in human metabotypes. This means that the same oral dose of EA or an ellagitannin-rich food may produce substantially different systemic exposures across individuals, complicating both efficacy and safety assessments.
Potential Concerns at High Doses
Among the mechanisms by which EA exerts its ameliorative effects is alteration of several growth factor expression levels and modulation of cell-cycle genes. It also protects against DNA damage and provides an extracellular complex with some toxins, which may reduce their interaction with cells. The dual role of EA in both promoting detoxification enzyme activity and suppressing certain CYP450 enzymes means interactions with co-administered pharmaceuticals remain a theoretically important but understudied concern in human settings.
Summary of Evidence Quality
The majority of published research on ellagic acid's specific biological effects consists of in vitro (cell-based) and animal model studies. A growing body of research documents mechanistic plausibility across multiple organ systems and disease conditions. Human clinical trial data is limited in quantity and scale — the most rigorous published human study to date is a randomized, double-blind, placebo-controlled trial in 32 participants with metabolic syndrome. Systematic reviews and meta-analyses have noted that effects observed robustly in animals — particularly for glycemic control — do not reliably translate to human populations at typical supplemental doses. Ellagic acid's poor intestinal bioavailability, high individual variability in gut microbial conversion to urolithins, and the complexity of distinguishing EA's own activity from that of its metabolites represent major limitations for interpreting the clinical evidence base. Novel delivery formulations, including phospholipid complexes and nanoparticle systems, are under investigation to address bioavailability challenges.
References
Volver