Ash (Fraxinus spp.) as a Dietary Supplement and Medicinal Botanical: A Comprehensive Reference
1. Identity, Taxonomy, and Natural Source
Fraxinus excelsior, known as the ash, European ash, or common ash, is a flowering plant species in the olive family Oleaceae. It is native throughout mainland Europe east to the Caucasus and Alborz mountains, and west to Great Britain and Ireland. The genus Fraxinus is large and widespread: the trees of the genus Fraxinus are found in the Northern Hemisphere, with around 60 species, the most common being the common ash (F. excelsior).
Several species carry particular medicinal relevance:
- Fraxinus excelsior L. — Common or European ash: the principal species used in European herbal medicine, whose leaves (Fraxini folium) are officinal in the European Pharmacopoeia.
- Fraxinus angustifolia Vahl — Narrow-leaved ash: its distribution covers central-southern Europe and northwest Africa and is a co-official source of Fraxini folium alongside F. excelsior.
- Fraxinus ornus L. — Manna ash or flowering ash: particularly well adapted to the dry and warm regions of Europe, especially the Mediterranean rim, and of smaller size than the common ash, reaching about ten metres. It is the primary commercial source of manna.
- Fraxinus chinensis Roxb. and related subspecies — Chinese ash: the sources of Fraxini cortex (also known as Qin-pi in China), with four Fraxinus spp. selected for medicinal purposes.
The genus name Fraxinus is derived from the Greek phraxis (meaning splitting or separation) because the wood is easy to split, which is why it was used in the past to make spears and tools. The species epithet excelsior refers to the size of the tree (Latin for "higher, loftier").
In the 10th edition of the European Pharmacopoeia, two monographs are presented: Fraxini chinensis cortex standardised on coumarins and Fraxinis folium standardised on hydroxycinnamic acid derivatives.
Common Preparations and Forms
The dried leaves (Fraxini folium) harvested in early summer and the bark (Fraxini cortex) of younger twigs are used. Beyond these official forms, ash is encountered as:
- Dried leaf infusions (herbal teas)
- Hydroethanolic or aqueous extracts in tincture or liquid extract form
- Standardised seed/fruit extracts (e.g., FraxiPure™ and Glucevia®, standardised for secoiridoid glycosides nuzhenide and GI-3)
- Manna — the dried exudate of F. ornus, available as flake, powder, or "tears"
- Multi-plant phytopharmaceutical preparations, such as PHYTODOLOR (Germany, Switzerland), which associates alcoholic tinctures of trembling poplar (Populus tremula), ash (Fraxinus excelsior), and goldenrod (Solidago virgaurea).
2. Traditional and Historical Use
Ancient Greece and Rome
Hippocrates used F. excelsior leaves and bark as diuretics and for the treatment of rheumatism, fever, wounds, diarrhoea, and dysentery. The earliest known mention of Fraxinus ornus dates back to Dioscorides' De Materia Medica (1st century CE), where "manna" from ash trees was noted as a mild laxative. Roman writers like Pliny the Elder praised its sweet sap as a subtle remedy for respiratory discomfort.
Medieval and Renaissance Europe
Its uses as a medicinal herb were already known by the Greek physician Hippocrates (460–377 BC). St. Hildegard of Bingen (1098–1179), a German writer, composer, and philosopher, wrote of using ash as a treatment for gout and rheumatism. The bark of F. excelsior had considerable reputation at one time in Europe as a remedy for intermittent fevers. The leaves, which are laxative and purgative according to the quantity taken, have been used successfully in gouty and arthritic rheumatic complaints.
European Folk and Herbal Traditions
Bark was utilised for treating fevers, while leaves were applied to address gout and promote improved urinary and digestive functions; ash sap was employed to ease earaches. The tree was also used to treat jaundice, kidney and bladder stones, flatulence, warts, ringworm, and earache. The ash bark has been used as a fever-reducing agent and as a substitute for quinine; the bark and leaves have been used traditionally as an herbal remedy for diarrhoea.
According to European traditional phytotherapy, the ash leaf is considered "draining," depurative, and protective, promoting the elimination of substances that accumulate in the body.
Traditional Chinese Medicine (TCM)
Ash tree bark (Qin Pi) has been used in Traditional Chinese Medicine for over 2,000 years and is referenced in one of the first texts of Chinese medicine, The Divine Farmer's Materia Medica. Known as Qin-pi, Chinese ethnic minorities mainly use the roots and whole plants to treat stomatitis, haemostasis, and excretory organ infections, while the Han tribe primarily uses its bark for similar therapeutic effects.
Central and South Asian Traditions
In northern areas of Pakistan, root bark and leaves of Fraxinus plant have been traditionally used for the cure of malaria and pneumonia.
Manna in Mediterranean and Sicilian Traditions
The flowering or manna ash is cultivated in Europe for its sweet bark exudates, which have been used as a nutritive tonic medicine and mild laxative for many centuries. Manna was harvested by making incisions in the bark of cultivated F. ornus trees, particularly in Sicily and Calabria (southern Italy). Manna is primarily used as a mild laxative, in the regulation of intestinal function, and to a lesser extent as a fluidising expectorant and cough suppressant.
3. Key Chemical Constituents and Active Compounds
Phytochemical investigations on Fraxinus species reveal the occurrence of a wide range of chemical compounds including coumarins, secoiridoids, phenylethanoids, lignans, flavonoids, and simple phenolics. Out of the 155 different components described in one comprehensive review, 78 belong to the groups of the coumarins and secoiridoids.
Coumarins
Coumarins are the most distinctive and well-investigated class of compounds in Fraxinus. The occurrence of coumarins distinguishes the genus Fraxinus from the other genera in the Oleaceae. Esculetin, esculin, cichoriin, scoparone, fraxetin, fraxin, and fraxinol are among the most frequently found.
- Esculin: A glycosidic coumarin derivative (6-beta-glucoside-7-hydroxycoumarin, molecular formula C₁₅H₁₆O₉) whose two parts (glucose and 7-hydroxycoumarin) are linked by an ester linkage through oxygen. The oral bioavailability of esculin is only 0.62%; it can be enzymatically hydrolysed to yield esculetin and glucose.
- Esculetin: The aglycone metabolite of esculin (6,7-dihydroxy-2-chromenone, molecular formula C₉H₆O₄), one of the simplest coumarins with two hydroxyl groups at carbons 6 and 7; its average oral bioavailability is 19%, significantly higher than that of esculin.
- Fraxin and fraxetin: Additional characteristic coumarins present throughout the genus.
- Isofraxidin: Isofraxidin emerges as a pivotal player among ash bark coumarins, with its multifaceted pharmacological activities including potent anti-inflammatory attributes warranting thorough exploration.
Secoiridoids
Secoiridoid glycosides present in F. excelsior include phenylethanoid glycosides such as verbascoside, salidroside, calceolarioside A and B, lugrandoside, isolugrandoside, and isoacteoside. The secoiridoids nuzhenide and GI-3 are the key marker compounds standardised in the seed extract products FraxiPure™ and Glucevia®. The secoiridoids were found to possess potent coronary vasodilating activity.
Phenylethanoids and Lignans
Compounds including ligstroside, formoside, and oleoacteoside have been isolated from ash leaves and shown anti-inflammatory activity. A range of chemical constituents including secoiridoids, phenylethanoids, lignans, flavonoids, and coumarins has been isolated from Fraxinus plants.
Flavonoids and Phenolic Acids
Phenolic compounds identified in F. excelsior include p-hydroxybenzoic acid, protocatechuic acid, vanillic acid, syringic acid, 2,4-dihydroxybenzoic acid, and gallic acid, together with flavonoids, sterols, and triterpenes. Ash leaves contain flavonoids, hydroxycinnamic acid derivatives, iridoid bitter substances, and tannins; ash bark contains iridoid bitter substances and coumarins.
Manna Constituents
Manna on average contains 40–60% mannitol or mannite (C₆H₁₄O₆), 8–10% humidity, 3–5% glucose and fructose, 12–16% manninotriose, 6–12% manninotetrose, 1–3% mineral elements, and 0.5–0.1% resin among other minor quantities. Manna also contains a fluorescent compound called fraxin, which occasionally gives a greenish colour to manna sugar and may be an active purgative compound, plus some phenolic acids (elenolic acid, pinoresinol, homovanillic acid), a small quantity of mucilage, and minerals.
4. Mechanisms of Action
Anti-inflammatory Activity
STW1 (Phytodolor®), which contains common ash bark (Fraxinus excelsior), belongs to the group of anti-inflammatory and antirheumatic drugs, and is authorised for the treatment of painful disorders of degenerative and inflammatory rheumatic diseases. The individual components have complementary effects; its multifocal mode of action includes antiphlogistic, analgesic, antiexudative, antioxidative, antipyretic, and antiproliferative properties. At the cellular level, compounds isolated from ash leaves — including ligstroside, formoside, and oleoacteoside — show the ability to increase IL-10 receptor expression on the surface of monocyte/macrophage cells stimulated by LPS, and to decrease secretion of pro-inflammatory cytokines TNF-α and IL-6.
Diuretic Activity
Extracts from the leaves of Fraxinus excelsior are traditionally used to facilitate renal excretion; this diuretic activity is attributed to the presence of flavonoids.
Hypoglycaemic / Glucose-Modulating Activity
Secoiridoid-rich seed extracts are thought to modulate glucose homeostasis. The seeds are not traditionally used but several recent studies have revealed pharmacological potential related notably to the presence of glucosides of secoiridoids; these extracts have been shown to act on the metabolism of glucose and blood lipids in ways relevant to mitigating type 2 diabetes and its consequences (metabolic syndrome) or to accompanying dietary regimes.
Laxative (Osmotic) Activity of Manna
Manna's most abundant active compound is the hexavalent alcohol D-mannitol, also known as "manna sugar," an osmotically active cell-compatible polyol responsible for the consolidated use of manna as a natural remedy against constipation and as a sweetener. Mechanistically, mannitol's osmotic effect holds the lead in the laxative action, pulling water into the colon without aggressive spasms.
Antimicrobial Activity
The ethyl ether fraction of F. excelsior bark ethanolic extract has inhibitory effects against Bacillus subtilis; F. excelsior leaves extract has antifungal activity against Gloeosporum limetticola and Alternaria tenuis; and the leaves' aqueous extract has been found to suppress growth of Candida albicans, while its bark aqueous extract showed antimicrobial activity against Staphylococcus aureus and Proteus mirabilis.
Hepatoprotective and Choleretic Activity
The liver-protecting properties of some coumarin and flavonoid components of Fraxinus spp. are reported in the literature. Isofraxidin and scopoletin exert pronounced choleretic activity; quercetin was found to increase bile secretion and the detoxifying function of the liver in experimental animals.
5. Scientific Evidence by Area of Health Use
5.1 Musculoskeletal and Rheumatic Conditions (Anti-inflammatory / Analgesic)
Fraxinus excelsior bark is one component of the fixed-combination phytomedicine Phytodolor® (STW1). This product has the most substantial clinical evidence base for any ash-containing preparation.
Preclinical evidence: Aqueous/alcoholic extracts of Populus tremula, Solidago virgaurea, and Fraxinus excelsior (components of Phytodolor N) were tested individually and in three different combinations for anti-inflammatory activity using carrageenan-induced oedema and/or adjuvant-induced arthritis of the rat paw. The tested combinations as well as the individual extracts significantly reduced paw oedema to varying degrees and also dose-dependently inhibited the arthritic paw volume; the anti-inflammatory activity of the combinations was comparable to tested doses of diclofenac.
Clinical evidence (systematic review): Phytodolor, a standardised extract of Populus tremula, Fraxinus excelsior, and Solidago virgaurea, was evaluated in clinical trials. Regimens used included 3×30 drops/day at half, normal, and double strength; 3×40 drops/day; and 2×2 tablets/day (each equivalent to 50 drops). Comparator interventions included placebo or active drugs including diclofenac (3×25 mg/day), piroxicam (20 mg/day), and indomethacin (2×50 mg/day). Treatment duration ranged from two to four weeks in people suffering from musculoskeletal pain including osteoarthritis, chronic epicondylitis, rheumatic arthritis, and various other rheumatic diseases.
A comprehensive review of published and unpublished studies on STW1 (Phytodolor®) concluded that STW1 (Phytodolor®) contains a fixed combination of extracts from aspen leaves and bark (Populus tremula), common ash bark (Fraxinus excelsior), and goldenrod herb (Solidago virgaurea) and belongs to the group of anti-inflammatory and antirheumatic drugs, authorised for the treatment of painful disorders of degenerative and inflammatory rheumatic diseases.
Limitations: The available clinical evidence concerns the multi-herb combination STW1/Phytodolor®, not ash as an isolated ingredient. The contribution of F. excelsior bark specifically — versus the other components — cannot be separated from these trials. Evidence for ash leaf as a standalone anti-inflammatory agent in clinical settings remains limited; the efficacy of ash leaves in clinical studies has not been confirmed.
EMA position: According to the European Medicines Agency, in European traditional medicine, ash leaves are recommended to treat minor articular pain and to increase the amount of urine for flushing in minor urinary complaints. This classification is based on traditional use, not clinical evidence of efficacy from controlled trials.
5.2 Glucose Homeostasis and Metabolic Health
This is the most thoroughly investigated area for Fraxinus excelsior seed extracts specifically.
Acute clinical trial (2009): The clinical efficacy and safety of the seed extract FraxiPure™ (Naturex), containing 6.8% nuzhenide and 5.8% GI-3 (w/w), on plasma glucose and insulin levels was assessed against glucose (50 g) induced postprandial glycaemia; a preselected dose of 1.0 g was used in a double-blind, randomised, crossover, placebo (wheat bran) controlled study on 16 healthy volunteers. The extract lowered incremental postprandial plasma glucose concentration compared to placebo at 45 min (P=0.06) and 120 min (P=0.07); it statistically (P=0.02) reduced the glycaemic area under the blood glucose curve; the seed also induced a significant (P=0.002) secretion of insulin at 90 min after glucose administration; however, the insulinaemic area under the blood insulin curve was not different from placebo; no adverse events were reported. These findings confirmed the hypoglycaemic action of the seed extract.
Longer-term clinical trial (2014): A study titled "A Fraxinus excelsior L. Seeds/Fruits Extract Benefits Glucose Homeostasis and Adiposity Related Markers in Elderly Overweight/Obese subjects: A Longitudinal, Randomized, Crossover, Double-blind, Placebo-controlled Nutritional Intervention Study" was published in Phytomedicine in April 2014. This trial, conducted at the University of Navarra (Pamplona, Spain), examined the Glucevia® extract. The nuzhenide and GI-3 content of the Glucevia® extract were respectively 7.04% and 3.49%.
Limitations: The 2009 acute study was small (n=16), crossover, and single-dose; the postprandial glucose reductions at individual timepoints did not reach conventional statistical significance (P=0.06 and P=0.07). The findings encouraged conducting long-term clinical studies to further evaluate the efficacy and safety of the seed extract in healthy and diabetic volunteers and to explore the possible mechanisms of action. Multiple studies in this area were funded by or conducted in collaboration with Naturex, the manufacturer of the extracts, which represents a potential source of bias. Animal model data is more abundant than robust human trial data in this area.
5.3 Laxative Effects (Manna / F. ornus)
Manna is produced from the spontaneous solidification of the sap of some Fraxinus species, and, owing to its content in mannitol, is used in medicine as a mild laxative. Manna sugar (mannitol) was formerly used in medicine as a gentle laxative, but is now chiefly used as a children's laxative or to disguise other medicines. The mechanism is well-established pharmacologically, mannitol being a recognised osmotic agent. Clinical evidence specific to manna as a laxative preparation derives largely from traditional use records and limited controlled investigations, primarily from Italy.
5.4 Antimicrobial Activity
Metabolites and extracts from Fraxinus plants have been found to possess a variety of biological activities including antimicrobial activity. However, this evidence is almost entirely from in vitro or preclinical studies. No human clinical trials have evaluated ash preparations specifically for infectious disease management. The antimicrobial data is considered preliminary and mechanistically interesting, but is not sufficient to support clinical claims.
5.5 Diuretic and Urinary Tract Support
The diuretic and urinary flushing action of ash leaf is recognised by the European Medicines Agency as a traditional use. Ash leaf can be used to treat a common or recurrent urinary infection (cystitis), but is considered less effective than extracts of Ericaceae (cranberry, heather, blueberry). No controlled human clinical trials have been identified that demonstrate ash leaf's efficacy as a standalone diuretic in a rigorous trial setting; the EMA indication therefore rests on traditional use evidence.
5.6 Neuroprotective Activity (Preclinical Only)
In a rat model of aluminium chloride-induced Alzheimer's disease, F. excelsior bark extract significantly improved memory and cognitive function, maintained weight, prevented neuronal damage, and preserved the hippocampus's histological features. The extract increased anti-inflammatory MMP-2 activity, decreased inflammatory MMP-9, and increased plasma antioxidant capacity by enhancing catalase and glutathione while decreasing nitrite levels; the highest therapeutic effect was seen in rats receiving 200 mg/kg. The extract, rich in coumarins, was proposed as a potentially effective anti-Alzheimer adjunct agent acting through antioxidant and anti-inflammatory pathways. This evidence is preclinical (animal model) only and cannot be extrapolated to humans.
5.7 Anticancer Activity (In Vitro Only)
One study assessing the activity of a hydrophilic extract of manna (HME) from Fraxinus angustifolia on cellular and molecular events in human colon-rectal cancer cells found that HME showed a time- and concentration-dependent anti-proliferative activity, measured by MTT assay, in all cell lines examined (Caco-2, HCT-116, and HT-29). The amounts of HME causing 50% cell death after 24 h treatment were 8.51, 10.73, and 28.92 mg manna equivalents/mL, respectively. This is in vitro data only; no human studies have evaluated ash or manna for cancer.
6. Body Systems and Health Areas of Association
- Musculoskeletal system: Joint pain, osteoarthritis, rheumatic conditions (via combination phytomedicines; traditional use for gout).
- Metabolic system: Postprandial blood glucose management, adiposity markers, metabolic syndrome (seed/secoiridoid extracts).
- Digestive system: Mild laxative action (manna/mannitol); traditional use for constipation and intestinal regulation.
- Urinary system: Diuretic effect; traditional use for urinary flushing and minor urinary complaints.
- Immune and inflammatory pathways: Modulation of cytokine secretion (TNF-α, IL-6, IL-10) demonstrated in vitro.
- Cardiovascular system: Preliminary evidence of secoiridoid-related coronary vasodilation; antioxidant effects relevant to vascular protection.
- Hepatobiliary system: Choleretic and potentially hepatoprotective effects from coumarin and flavonoid constituents (primarily preclinical).
- Nervous system: Neuroprotective activity in animal models only (bark extract, aluminium-induced neurodegeneration model).
7. Dosage Forms and Reported Dosages
Dosages cited in the scientific literature and from regulatory sources are as follows:
- Seed extract (FraxiPure™ / Glucevia®) — glucose studies: A preselected dose of 1.0 g of seed extract (containing 6.8% nuzhenide and 5.8% GI-3) was used in the acute crossover study on 16 healthy volunteers.
- Phytodolor® (multi-herb combination containing ash bark): Actual regimens used in clinical trials included 3×30 drops/day at half, normal, and double strength; 3×40 drops/day; and 2×2 tablets/day (each tablet equivalent to 50 drops).
- Ash bud glycerine maceration: Preparation as 5 to 15 drops per day, or 50 drops three times daily of the glycerine maceration in 1D dilution (1/10), as cited in European phytotherapy practice.
No standardised recommended daily dose for standalone ash leaf preparations has been established by the EMA's HMPC under full efficacy criteria; dosing for traditional use indications is guided by national herbal medicine traditions and pharmacopoeia monographs.
8. Safety Considerations and Interactions
Coumarin Content and Anticoagulant Risk
A common concern with coumarin-containing plants is the potential for anticoagulant interactions. The EMA assessment report on ash leaf addresses this directly: coumarin compounds detected in ash leaf do not possess the minimum structural requirements (a C-4 hydroxyl substituent and a C-3 non-polar carbon substituent) for anticoagulant activity. This is a significant pharmacological distinction between the coumarins present in ash leaf and the anticoagulant coumarins such as warfarin (a dicoumarol derivative). However, esculetin, a coumarin derivative present in ash, has been investigated for its ability to prevent thrombosis through inhibitory signalling on PLCγ2-PKC-AKT activation in human platelets, suggesting some antiplatelet-relevant activity that warrants attention in patients on antiplatelet therapy, even if classical anticoagulant risk is low.
Photosensitisation
Esculetin, esculin, and isoscopoletin showed a local photosensitising effect in an animal study; however, neither these coumarins nor any other similar structures were reported to be photosensitising after oral administration.
Seed Extract Safety
FraxiPure™ is described as a safe natural extract obtained from F. excelsior that was shown to reduce glycaemia in animal models and human clinical trials. A formal safety and nutritional composition evaluation (Flanagan et al., 2013, Food Chemistry and Toxicology) was conducted on the FraxiPure™ seed extract, demonstrating safety and tolerability in healthy subjects.
Gastrointestinal Tolerance
No adverse events were reported in the acute clinical trial of seed extract (1.0 g dose, n=16). At higher doses, gastrointestinal side effects such as nausea or loose stools are theoretically possible, particularly from leaf preparations with their mild laxative action, though formal dose-response safety data in humans is limited.
Esculin Oral Bioavailability
The oral bioavailability of esculin is only 0.62%, substantially limiting the systemic exposure from oral preparations standardised on esculin content. This low bioavailability should be considered when interpreting in vitro pharmacological data on esculin.
Allergenicity
Ash pollen (F. excelsior) is a well-recognised inhalant allergen in Europe and contributes to pollinosis. Cross-reactivity between ash pollen and oral ash preparations has not been formally documented in the peer-reviewed clinical literature, but individuals with documented severe ash pollinosis should note this botanical relationship.
Long-term Safety Data Gaps
The results from the acute seed extract study encourage conducting long-term clinical studies to further evaluate the efficacy and safety of Fraxinus excelsior L. seed extract in healthy and diabetic volunteers. Long-term controlled human safety data remain unavailable for most ash preparations.
Drug Interactions
No direct pharmacokinetic drug interaction studies have been published for ash preparations. The potential for additive hypoglycaemic effects with antidiabetic medications is a theoretical concern given the documented postprandial glucose-lowering effects of the seed extract and would merit monitoring. The coumarin content of ash leaf does not appear to carry conventional anticoagulant drug interaction risk based on structural analysis by the EMA, though antiplatelet effects of esculetin have been noted in preclinical work.
References
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