Hydroxytyrosol

Hydroxytyrosol: A Comprehensive Reference

1. Identity, Chemistry, and Natural Sources

Chemical Identity

Hydroxytyrosol (IUPAC name: 4-(2-Hydroxyethyl)-1,2-benzenediol) is a molecule with potent antioxidant activity. It is an organic compound with the molecular formula (HO)₂C₆H₃CH₂CH₂OH and is classified as a phenylethanoid — a relative of phenethyl alcohol. It is a phenolic alcohol abundant in olive leaves and fruits, with the chemical formula C₈H₁₀O₃ and a molecular weight of 154.164 g/mol. Structurally, it is a derivative of catechol. The compound is commonly abbreviated as HT, DOPET (3,4-dihydroxyphenylethanol), or 3,4-DHPEA in the scientific literature. Hydroxytyrosol is a colorless solid, although samples often turn beige during storage.

Hydroxytyrosol can be extracted from olive leaves and oil, is stable in the free form, and penetrates readily into tissues. Its chemical formula C₈H₁₀O₃ is identical to tyrosol except for an extra hydroxyl group in the meta-position of the aromatic ring. It is soluble in lipids but is also slightly soluble in water, and can exist as a simple phenol or as acetate or secoiridoid derivatives.

Natural Sources and Occurrence

Hydroxytyrosol is derived from the hydrolysis of oleuropein during the maturation of olives. It is a natural compound found in olive leaves and oil, with the main dietary source being extra virgin olive oil (EVOO). The olives, leaves, and olive pulp contain large amounts of the hydroxytyrosol derivative oleuropein. Unprocessed, green (unripe) olives contain between 4.3 and 116 mg of hydroxytyrosol per 100 g of olives, while unprocessed, black (ripe) olives contain up to 413.3 mg per 100 g.

A high concentration of HT is found in olive leaves; however, this is lost as a residue during oil production, and to reduce industrial waste, the residue is used to obtain natural products used in the food, cosmetics, and pharmaceutical industries. Processed olives, such as the common canned variety containing iron(II) gluconate, contain little hydroxytyrosol, as iron salts are catalysts for its oxidation. Hydroxytyrosol and its derivatives are also found in a variety of other natural sources, notably wines.

Virgin olive oils (VOO) and extra virgin olive oils (EVOO) contain 97–99% lipids, mostly triglycerides, and 1–3% minor components including phenolic compounds derived from oleuropein and ligstroside — notably hydroxytyrosol and tyrosol. The daily intake of hydroxytyrosol within the Mediterranean diet is estimated to be between 0.15 and 30 mg.

Common Forms and Preparations

Hydroxytyrosol is obtained from vegetation water (i.e., waste water derived from the processing of olive oil) or from olive leaves through a process in which liquid rich in phenols is extracted and purified. In the supplement industry, it is available in multiple forms. The biotechnological production of HT involves the use of biological methods, such as enzymes or microorganisms, to synthesize HT. Certain chemical synthesis methods may require harsh reaction conditions, such as high temperatures or strong acids, while chemical synthesis methods offer advantages such as high purity and scalability but may have drawbacks such as expensive substrates and the use of heavy metal catalysts.

Commercial preparations include standardized olive fruit extracts (such as Hytolive®), olive leaf extracts, and isolated pure hydroxytyrosol. It is also available as hydroxytyrosol acetate and as phosphatidyl-hydroxytyrosol (a phospholipid-bound form). The process for obtaining hydroxytyrosol from olive leaves was patented in 2004. Due to its bioavailability, chemical properties, and easy formulation along with its lack of toxicity, hydroxytyrosol is considered an excellent food supplement by the nutraceutical and food industries.

2. Traditional and Historical Use

The olive tree (Olea europaea) has a recorded history of approximately 6,000 years. Olives are a traditional symbol of the Mediterranean diet, and hydroxytyrosol is an olive-derived compound known for its antioxidant and cardioprotective effects. While hydroxytyrosol as an isolated phytochemical was not identified until the modern era of analytical chemistry, the use of olive-derived preparations containing it as a major constituent has a rich historical record across Mediterranean civilizations.

Historically, olive leaf has been one of the famous herbal teas in the Mediterranean and is a popular prophylaxis as well. The ability of oleuropein — the primary precursor of hydroxytyrosol in olive leaves — to lower blood pressure may justify the traditional use of olive leaf in the treatment of mild to moderate hypertension. Ancient Egyptians, Greeks, and Romans used olive leaf decoctions and olive oil medicinally. Within the traditional practice of these cultures, such preparations were applied to treat fevers, infections, and wound healing. The observation that Mediterranean populations, who consumed large quantities of olive oil, had lower rates of cardiovascular disease eventually led researchers to systematically investigate its phenolic constituents, including hydroxytyrosol.

In recent years, the phytoconstituents of foods in the Mediterranean diet, described as a diet heavy in vegetable oils, fruits, nuts, and fish, have been the subject of several studies for their beneficial effects on human health. The most studied element of the Mediterranean diet is olive oil, and several studies have attributed these protective effects to hydroxytyrosol, the main polyphenol contained in olive oil and leaves.

It is important to distinguish that in traditional practice, it was whole olive oil, olive leaf tea, or olive-based preparations — not isolated hydroxytyrosol — that were employed. The isolation, characterization, and dedicated supplementation of hydroxytyrosol as a pure compound is a development of late twentieth and early twenty-first century nutritional science. The first analyses of olive by-products began in 1999, and the number of research publications related to this compound subsequently grew to more than 21,400.

3. Key Constituents and Mechanisms of Action

Structural Basis of Bioactivity

The catechol moiety of hydroxytyrosol represents the principal reactive site responsible for radical scavenging. The ortho-dihydroxyl arrangement facilitates hydrogen atom donation and stabilization of phenoxy radicals through resonance delocalization, interrupting radical chain reactions. Density functional theory (DFT) studies support the relatively low bond dissociation energy of these hydroxyl groups compared to several other phenolic antioxidants, consistent with efficient hydrogen atom transfer (HAT) activity.

Hydroxytyrosol has a strong antioxidant activity due to its high capacity to eradicate both intracellular and extracellular production of reactive oxygen species (ROS), being mainly effective with free radical molecules such as superoxide (O₂⁻) and hydrogen peroxide (H₂O₂), and acting as a metal chelator as well. These properties are due to both the presence of hydroxyl (OH) groups in the ortho position, which have electron-donating capacity, and to HT's ability to bind phenoxyl radicals, forming stable hydrogen bonds.

Antioxidant Mechanisms

The antioxidant effects of hydroxytyrosol arise from multiple well-characterized physicochemical mechanisms, including direct free radical scavenging, metal ion chelation, and modulation of endogenous antioxidant defense systems. HT can neutralize reactive oxygen species through hydrogen atom transfer (HAT) mechanisms, in which phenolic hydroxyl groups donate hydrogen atoms to peroxyl radicals, forming relatively stable phenoxy radicals that interrupt radical chain reactions. In addition, HT exhibits iron and copper chelation properties, thereby limiting metal-catalyzed Fenton reactions and subsequent hydroxyl radical generation.

Beyond direct scavenging, hydroxytyrosol activates cellular antioxidant signaling cascades. HT can activate antioxidant enzymes that scavenge ROS and promote the expression of Nrf2-dependent genes, including γ-Glutamyl Cysteine Ligase (γ-GCL), heme oxygenase-1 (HO-1), NAD(P)H:quinone oxidoreductase (NQO1), and thioredoxin reductase (TrxR), inhibiting the generation of ROS and vascular damage, and actively regulating the antioxidant defense system in vascular endothelial cells. In addition to these mechanisms, HT can also directly scavenge free radicals and destroy free radical chain reactions, preventing the generation of large numbers of new free radicals, thereby reducing oxidative stress damage caused by excessive free radicals.

Hydroxytyrosol also induces the nuclear transcription factor Nrf2, a transcription factor implicated in the expression of several antioxidant and detoxifying enzymes. Two important signaling proteins involved in Nrf2 translocation — protein kinase B and extracellular regulated kinases — are also activated by HT. Studies with specific inhibitors have confirmed that both molecular pathways are critical for the nuclear translocation of Nrf2, increased enzyme expression and activity, and the beneficial effect against oxidative stress induced by HT. Together with the inherent radical scavenging activity of HT, these results provide an additional mechanism of action to prevent oxidative stress damage through modulation of signaling pathways involved in antioxidant and detoxifying enzyme regulation.

HT's strong antioxidant properties are due to the scavenging of radicals and the stimulation of synthesis and activity of antioxidant enzymes (SOD, CAT, HO-1, NOS, COX-2, GSH), which also limit the lipid peroxidation of low-density lipoprotein (LDL) cholesterol — a hallmark of atherosclerosis.

Anti-Inflammatory Mechanisms

Hydroxytyrosol has a strong antioxidant and free radical scavenger action, as it increases the activity of antioxidant enzymes and restores the oxidative balance. Among its main properties, HT also has an anti-inflammatory effect, mainly due to the inhibition of the NF-κB pathway and the release of inflammatory cytokines.

HT activates the Nrf2/ARE pathway, promoting antioxidant enzyme expression, and induces autophagy through SIRT1 activation. Simultaneously, it inhibits pro-inflammatory NF-κB and JAK/STAT pathways, reducing cytokine production. HT also promotes apoptosis by increasing the expression of p53, BAX, and caspase-3. It acts on cellular pathways such as Nrf2, NF-κB, JAK/STAT, PI3K/Akt, and SIRT1, regulating redox balance, inflammation, programmed cell death, and autophagy, and can also influence gene expression through epigenetic mechanisms.

Other Characterized Mechanisms

Hydroxytyrosol is considered the most powerful antioxidant compound after gallic acid and one of the most powerful antioxidant compounds among phenolic compounds from the olive tree, followed by oleuropein, caffeic acid, and tyrosol. Pre-clinical studies have identified tyrosol hydroxylation, mediated by cytochrome P450 isoforms CYP2A6 and CYP2D6, as an additional endogenous source of hydroxytyrosol in humans. HT also appears to inhibit monoamine oxidase (MAO) in the context of Parkinson's disease, potentially protecting against neurodegeneration.

4. Pharmacokinetics and Bioavailability

The intestinal microbiota has the ability to metabolize HT, which may influence its bioavailability and biological activity. HT enters the small intestine and is quickly absorbed; it can readily cross cell membranes due to its hydrophilic characteristics and very small molecular size. Following absorption, it quickly metabolizes to produce a variety of metabolites, mainly glucuronides and sulfates, which are eliminated in the urine.

In general, the bioavailability of HT is relatively high compared to that of other phenolic compounds. In both rats and humans, hydroxytyrosol is quickly absorbed, has a half-life of a few minutes, and is eliminated by the kidneys as either free hydroxytyrosol or in oxidized or conjugated forms (glucuronide and sulfate derivatives).

In a double-blind study including 20 volunteers who ingested 5 mg of hydroxytyrosol through diverse food matrices, the pharmacokinetics after consumption was found to be strongly dependent on the food matrix. The metabolic profile of hydroxytyrosol is influenced by the food matrix in which it is incorporated, with the oily nature being relevant for final bioavailability. Extra virgin olive oil was identified as the best matrix for this compound.

Because HT may pass across the blood–brain barrier, it can efficiently enter cells and tissues, including the brain, which increases its capacity to exhibit neuroprotective effects. Despite its rapid metabolism, HT can reach the brain in small but functional amounts, and various formulation methods can enhance its delivery to nervous tissue.

Pharmacokinetic analysis in rats indicates a fast and extensive uptake of the molecule by organs and tissues, with a preferential renal uptake. Approximately 90% of the administered radioactivity is excreted in urine collected up to 5 hours after injection, and about 5% is detectable in feces and gastrointestinal content. In all investigated tissues, DOPET is enzymatically converted into four oxidized and/or methylated derivatives. A significant fraction of total radioactivity is associated with sulfo-conjugated forms, which also represent the major urinary excretion products.

5. Scientific Evidence by Area of Health Use

5.1 Cardiovascular and Cardiometabolic Health

The growing incidence of cardiovascular disease has promoted investigations of natural molecules that could prevent and treat it. Among these, hydroxytyrosol, a polyphenolic compound of olive oil, is well known for its antioxidant, anti-inflammatory, and anti-atherogenic effects.

Regulatory endorsement: The European Food Safety Authority (EFSA) issued a scientific opinion on health claims in relation to dietary consumption of hydroxytyrosol and related polyphenol compounds from olive fruit and oil, and protection of blood lipids from oxidative damage which is known to adversely affect cardiovascular health (EFSA Journal 2011;9(4):2033). On the basis of the data presented, EFSA concluded that a cause-and-effect relationship has been established between the consumption of hydroxytyrosol and related compounds from olives and olive oil and protection of blood lipids from oxidative damage. Under Commission Regulation (EU) 432/2012, the approved health claim states: "Olive oil polyphenols contribute to the protection of blood lipids from oxidative stress," and may be used only for olive oil containing at least 5 mg of hydroxytyrosol and its derivatives (e.g., oleuropein complex and tyrosol) per 20 g of olive oil.

Human clinical evidence: Studies about purified polyphenols and HT supplementation in humans are still limited. Lowered inflammation and oxidative stress and an improved lipid profile were demonstrated in healthy subjects as well as in metabolic syndrome patients after hydroxytyrosol supplementation, which may open a new therapeutic scenario through personalized supplementation in cardiovascular disease prevention.

One randomized double-blinded, placebo-controlled crossover trial determined the effect in healthy volunteers of two gastroresistant capsules containing 15 mg/day of HT for a 3-week period, evaluating nutritional status, serum metabolites, oxidative stress biomarkers, and gene expression of 9 genes related to oxidative stress, inflammation, and cardiovascular disease. The results showed that 15 mg/day of HT consumption could exert positive effects on human health by reducing oxidative stress and cardiovascular risk and improving lipid and plasma antioxidant profiles, although this daily amount of HT did not appear to produce any positive effects on oxidized LDL cholesterol. The authors noted that setting the minimum supplementation of 5 mg/day of HT as recommended by EFSA, these results suggest a necessary personalization of HT doses to exert health benefits in cardiovascular disease prevention.

A meta-analysis evaluating the clinical effects of dietary supplementation with oleuropein (OLE), hydroxytyrosol (HT), and tyrosol (TYR) on cardiometabolic outcomes included fourteen human intervention studies with 594 participants. The analysis using a random-effects model showed that OLE, HT, and TYR significantly reduced total cholesterol (SMD = −0.19, p = 0.04), triacylglycerol (SMD = −0.32, p = 0.03), and insulin (SMD = −0.42, p = 0.04). However, this meta-analysis grouped multiple olive phenolics together, and results are not entirely attributable to HT alone.

In one clinical study, an interventional product containing 3.3 mg of HT, 65 mg of phosphatidylcholine, and 331.7 mg of maltodextrin was administered, and upon the intervention period, lipid profile improved noticeably: LDL decreased (p < 0.004), HDL increased (p < 0.033), and triglycerides decreased (p < 0.017).

Inconsistencies in human trials due to dose and population diversity limit firm conclusions. It remains unclear whether HT, when consumed as a supplement, effectively protects circulating LDL from oxidation as attributed to its role in EVOO-based health claims. Moreover, the relevance of these effects in populations at risk for non-communicable diseases is still uncertain, since most supporting evidence has been derived from studies conducted in healthy individuals, where antioxidant mechanisms may primarily act as preventive measures.

Evidence strength: Moderate for LDL oxidation protection when consumed as part of a high-polyphenol olive oil (sufficient for EFSA health claim endorsement). Preliminary-to-moderate for isolated HT supplementation effects on lipid profiles. Further large, long-duration randomized controlled trials with isolated HT are needed.

5.2 Neuroprotection and Cognitive Health

Hydroxytyrosol is a food-sourced phenolic phytochemical with anti-oxidant and anti-inflammatory properties. Adherence to a Mediterranean diet based on extra virgin olive oil, of which HT is one of the principal components, is beneficial for reducing the incidence of chronic neurodegenerative diseases and improving cognitive ability. Accumulating evidence indicates that HT exhibits neuroprotective effects on multiple neurological disorders and neuropathophysiological conditions.

Hydroxytyrosol has garnered attention during the last twenty years due to its important health benefits. It is a powerful antioxidant whose consumption offers several health effects, including neuroprotection and cognitive health benefits. HT is specifically associated with neuroprotective effects, which have prompted research into its potential to prevent cognitive decline, particularly in relation to Alzheimer's disease.

HT appears to inhibit monoamine oxidase (MAO) in patients with Parkinson's disease, protecting against neurodegeneration. Research has analyzed its chemical characteristics, bioavailability, and ability to cross the blood–brain barrier. Despite its rapid metabolism, HT can reach the brain in small but functional amounts, and various formulation methods can enhance its delivery to nervous tissue.

Evidence strength: Largely preclinical (in vitro and animal models). Direct human clinical trial evidence specifically for HT and neurodegenerative outcomes remains limited, and no well-powered randomized controlled trials on neurological endpoints in humans have been published as of the available literature. The epidemiological association between Mediterranean diet adherence and reduced neurodegeneration supports interest but does not isolate HT's contribution.

5.3 Anti-Inflammatory Effects

HT has been shown to be able to modulate the oxidative and inflammatory process in numerous chronic disorders, including intestinal and gastrointestinal pathologies. The principal mechanism is inhibition of the NF-κB pathway. HT could have a role in atherosclerosis homeostasis, where the initial inflammatory cascade activates the intracellular signaling pathway of nuclear factor (NF)-κB, which regulates inflammatory cytokines (interleukins IL-1, IL-6, IL-8, and TNF-α) and chemokines such as monocyte chemotactic protein (MCP-1).

A closer inspection of studies shows a significant improvement of lipid profile, antioxidant capacity, and inflammatory state. A note of caution is due regarding in vitro studies, as the lack of validated approaches makes it difficult to establish goodness of fit with in vivo and clinical research. However, animal and clinical studies are considered very encouraging, determining HT supplementation useful for inflammation, oxidative stress, endothelial function, and cardiovascular diseases in general.

Evidence strength: Strong mechanistic and in vitro evidence; animal model evidence supports anti-inflammatory actions. Human clinical data for inflammation specifically remain limited and mostly indirect (via inflammatory biomarkers in cardiovascular or metabolic syndrome trials).

5.4 Endothelial Function and Vascular Health

Hydroxytyrosol is an olive-derived compound known for its antioxidant and cardioprotective effects. Acknowledging the merit of antioxidants in maintaining endothelial function warrants the application of hydroxytyrosol in endothelial dysfunction salvage and recovery. Endothelial dysfunction (ED) is an impairment of endothelial cells that adversely affects vascular homeostasis. Hydroxytyrosol improves endothelial dysfunction, decreases oxidative stress, and is neuro- and cardio-protective.

Evidence strength: Preclinical evidence is substantial. Human clinical data are present in cardiovascular supplementation studies but no trials have been conducted with endothelial function as the primary endpoint.

5.5 Gastrointestinal and Gut Health

HT has been shown to be able to modulate the oxidative and inflammatory process in numerous chronic disorders, including intestinal and gastrointestinal pathologies, highlighting its potential role in modulating the molecular mechanisms underlying the development of inflammatory bowel diseases (IBDs) and gastrointestinal diseases. Preliminary data also suggest roles in microbiota modulation.

Evidence strength: Largely preclinical. Human clinical evidence for gastrointestinal endpoints is minimal.

5.6 Antimicrobial, Antiviral, and Antifungal Activity

Hydroxytyrosol has anti-inflammatory, anti-tumor, antiviral, antibacterial, and antifungal properties, as identified in a systematic review of PubMed and other literature databases.

Evidence strength: Primarily in vitro and mechanistic. No human clinical trials have specifically evaluated HT as an antimicrobial agent.

5.7 Anticancer Activity

Data from a variety of studies suggest that hydroxytyrosol targets different cancer types such as breast, prostate, colon, and thyroid. Recent work has established a neuro-protective role in Parkinson's disease and a critical role in the prevention of atherosclerosis and diabetes. In cell models, HT has shown inhibitory effects on tumor growth and activation of apoptosis, without affecting non-tumor cells.

These results support HT's possible usefulness as an adjunct in the treatment of certain tumors, although further studies in animal and human models are required.

Evidence strength: Entirely preclinical (cell cultures and animal studies). No human clinical trials have demonstrated anticancer efficacy for isolated HT as of the available evidence base. Caution is warranted in interpreting in vitro findings as clinically applicable.

5.8 Skin and Photoprotection

HT protects against UV radiation, having a dermoprotective effect. Skin is exposed daily to ultraviolet radiation, increasing the formation of free radicals, and HT and its metabolites act as radical scavengers for skin cells. In addition, HT significantly reduces DNA breakdown caused by ultraviolet B radiation.

Evidence strength: In vitro and early-phase evidence. No large-scale human trials on UV photoprotection or dermatological outcomes.

5.9 Metabolic and Glycemic Effects

Because of HT's molecular structure, its regular consumption reports important beneficial properties including anti-inflammatory, antimicrobial, antioxidant, and anticancer effects. These benefits include a reduction of blood glucose and LDL cholesterol, and improvement of insulin levels while reducing oxidized LDL in blood.

In the meta-analysis of RCTs on olive phenolics, supplementation with oleuropein, HT, and tyrosol significantly reduced insulin (SMD = −0.42, p = 0.04), though the high heterogeneity (I² = 78%) warrants caution.

Evidence strength: Preliminary. Specific human trials isolating HT's effects on glucose metabolism are limited. Effects on insulin in the meta-analysis should be interpreted with caution due to high heterogeneity and compound grouping.

6. Body Systems Associated with Hydroxytyrosol

• Cardiovascular system: LDL oxidation protection, lipid profile, endothelial function, anti-atherogenic activity
• Central nervous system: Neuroprotection, potential roles in Alzheimer's disease, Parkinson's disease, cognitive health
• Immune and inflammatory system: NF-κB inhibition, cytokine modulation, anti-inflammatory activity
• Gastrointestinal system: Gut mucosal protection, potential roles in inflammatory bowel disease
• Integumentary system: Skin antioxidant protection, UV photoprotection
• Endocrine/metabolic system: Blood glucose modulation, insulin sensitivity, lipid metabolism
• Cellular/antioxidant system: Activation of Nrf2/ARE pathway, upregulation of HO-1, SOD, CAT, GPx, NQO1

7. Dosage Forms and Doses Reported in Studies

The EFSA-approved health claim specifies that the beneficial effect is obtained with a daily intake of 20 g of olive oil containing at least 5 mg of hydroxytyrosol and its derivatives. One applicant specified that the olive oil to which the effect is attributed must contain at least 250 mg/kg of polyphenols, and that a daily amount of 30 g (i.e., 2 tablespoons), equal to 6 mg of hydroxytyrosol and its derivatives, should be consumed to achieve the claimed effect.

Across the published human clinical literature, the following doses have been specifically reported:

• 15 mg/day of HT administered as two gastroresistant capsules in a randomized double-blinded, placebo-controlled crossover trial for a 3-week period.
• 5 mg of hydroxytyrosol ingested through diverse food matrices in a double-blind crossover study in 20 volunteers, used to evaluate pharmacokinetics.
• A clinical intervention product containing 3.3 mg of HT (combined with 65 mg of phosphatidylcholine and 331.7 mg of maltodextrin) showing improved lipid profiles.
• In a crossover controlled study, 25 mg tyrosol capsules (one per standard drink of white wine) were used to investigate the endogenous conversion of tyrosol to hydroxytyrosol in 33 individuals at cardiovascular risk.

The daily intake of hydroxytyrosol within the Mediterranean diet as a whole is estimated to be between 0.15 and 30 mg. It is important to note that the available human clinical trials are heterogeneous in design, dose, formulation, and duration, which limits the derivation of a single evidence-based optimal supplemental dose.

8. Safety Considerations and Regulatory Status

Toxicological Data

Toxicological studies in rats found no adverse effects upon the induction of acute toxicity by injection of a single dose of 2 g of HT/kg body weight. Subchronic toxicity studies with oral gavage administration at daily doses of 5, 50, or 500 mg HT/kg body weight per day did not cause any adverse effects, though one study assumed the lowest observed adverse effect level at 500 mg HT/kg bw/day and a NOAEL of 250 mg/kg bw/day. The only difference noted was salivation before and after administration in all animals, which the authors attributed to the bitter taste of HT and the oily, dense formulation.

In a subchronic 90-day oral toxicity study in rats using dose levels of 5, 50, or 500 mg/kg body weight per day, the EFSA Panel considered the dose of 50 mg/kg bw per day to be the no observed adverse effect level (NOAEL) based on changes in body and organ weights in the highest dose group tested.

Genotoxicity

An in vitro human lymphocyte chromosomal aberration study reported that hydroxytyrosol (with or without metabolic activation) induced an increase in the number of cells with structural chromosome aberrations. In line with the EFSA guideline on testing for genotoxicity, an in vivo micronucleus test was required. Based on the studies subsequently provided, the EFSA Panel concluded that there is no concern with regard to potential genotoxicity of hydroxytyrosol as a novel food.

EFSA Novel Food Assessment

Taking into account that the anticipated daily intake of the novel food would be in the range of or even less than the exposure of hydroxytyrosol from the consumption of olive oils and olives, which has not been associated with adverse effects, and considering the similar kinetics of hydroxytyrosol in rats and humans, the EFSA Panel considers that the margin of exposure for the novel food at the intended uses and use levels is sufficient for the target population. The Panel concluded that hydroxytyrosol is safe under the proposed uses and use levels.

Considering the NOAEL of 50 mg/kg bw per day in the subchronic oral toxicity study and the maximum anticipated daily intake, the margin of exposure would result in 100 for children (3–9 years of age) and at least 200 for adolescents, adults (excluding pregnant and breastfeeding women), and elderly.

Regulatory Status

Hydroxytyrosol is considered safe as a novel food for human consumption in the European Union, with a no-observed-adverse-effect level of 50 mg/kg body weight per day, as evaluated by EFSA. In the United States, hydroxytyrosol is considered to be a safe ingredient (GRAS) in processed foods at levels of 5 mg per serving.

Nutritional Considerations and Data Gaps

Hydroxytyrosol supplementation of oils could be nutritionally disadvantageous when it supplements oils that replace olive oil in the consumers' diet, since it is the combination of HT with the monounsaturated fatty acid and other polyphenol matrix of olive oil that contributes to the documented health profile of the overall food. Requests for additional toxicological data on developmental safety and safety on long-term consumption of hydroxytyrosol as a novel food ingredient have been noted, as have comments on the lack of human studies specifically with the novel food.

Further clinical trials are needed on a larger population over a longer period to increase knowledge about therapeutic mechanisms and ensure efficacy and safety.

Drug and Food Interactions

Preclinical studies have identified tyrosol hydroxylation mediated by cytochrome P450 isoforms CYP2A6 and CYP2D6 as an endogenous source of hydroxytyrosol, indicating that HT metabolism may intersect with the CYP450 enzyme system. At the doses typically encountered through dietary olive oil consumption or supplement use, no clinically significant drug interactions have been reported in the peer-reviewed literature to date, but formal drug–interaction studies are not available. The potential for interactions with anticoagulants or antiplatelet agents via HT's effects on platelet aggregation has been raised in preclinical research but not confirmed in human trials.

References

• Bertelli et al. (2020). Hydroxytyrosol: A natural compound with promising pharmacological activities. Journal of Biotechnology, 309, 29–33. ScienceDirect.
• Minari & Okeke (2020). Wide Biological Role of Hydroxytyrosol: Possible Therapeutic and Preventive Properties in Cardiovascular Diseases. PMC / Cells.
• Medina-Vera et al. (2023). Hydroxytyrosol and Its Potential Uses on Intestinal and Gastrointestinal Disease. PMC / International Journal of Molecular Sciences.
• Hydroxytyrosol. Wikipedia (citing primary sources including EFSA and PubChem).
• Hydroxytyrosol | CID 82755. PubChem, NIH.
• Martinez et al. (2018). Hydroxytyrosol: Health Benefits and Use as Functional Ingredient in Meat. PMC / Medicines.
• Hydroxytyrosol isolation, comparison of synthetic routes and potential biological activities. PMC, 2024.
• EFSA Panel on Dietetic Products, Nutrition and Allergies (2011). Scientific Opinion on olive oil polyphenols and protection of blood lipids from oxidative damage. EFSA Journal 9(4):2033.
• EFSA (2025). Olive oil polyphenols and the maintenance of normal HDL-cholesterol concentrations: Evaluation of a health claim. EFSA Journal.
• Hydroxytyrosol and Brain Tumors: Mechanisms of Action and Therapeutic Potential. PMC, 2025.
• Hydroxytyrosol: biological activities and potential application in livestock production. PMC, 2025.
• Hydroxytyrosol as a multitarget pharmacological agent for oxidative, inflammatory and metabolic disorders. Discover Molecules, Springer, 2026.
• Martín et al. (2010). Hydroxytyrosol induces antioxidant/detoxificant enzymes and Nrf2 translocation via ERK and PI3K/PKB pathways in HepG2 cells. Molecular Nutrition & Food Research.
• Boronat et al. (2020). Cardiovascular benefits of tyrosol and its endogenous conversion into hydroxytyrosol in humans. A randomized, controlled trial. Free Radical Biology and Medicine.
• Data on the endogenous conversion of tyrosol into hydroxytyrosol in humans. PMC / Data in Brief, 2019.
• Colica et al. (2017). Antioxidant Effects of a Hydroxytyrosol-Based Pharmaceutical Formulation on Body Composition, Metabolic State, and Gene Expression: A Randomized Double-Blinded, Placebo-Controlled Crossover Trial. PMC / Oxidative Medicine and Cellular Longevity.
• Alcaide-Hidalgo et al. (2023). Hydroxytyrosol: Its role in the prevention of cardiovascular diseases. PMC / Nutrients.
• Domínguez-Perles et al. (2020). Pharmacokinetics and bioavailability of hydroxytyrosol are dependent on the food matrix in humans. European Journal of Nutrition.
• Hydroxytyrosol: A Promising Therapeutic Agent for Mitigating Inflammation and Apoptosis. PMC, 2024.
• Pharmacokinetics of Hydroxytyrosol and Its Sulfate and Glucuronide Metabolites after the Oral Administration of Table Olives to Sprague-Dawley Rats. PMC, 2024.
• D'Angelo et al. (2001). Pharmacokinetics and metabolism of hydroxytyrosol, a natural antioxidant from olive oil. Drug Metabolism and Disposition, 29:1492–1498. PubMed.
• The Pharmaceutical Formulation Plays a Pivotal Role in Hydroxytyrosol Pharmacokinetics. PMC.
• EFSA Panel on Dietetic Products, Nutrition and Allergies (2017). Safety of hydroxytyrosol as a novel food pursuant to Regulation (EC) No 258/97. EFSA Journal 15(2):4728.
• Safety of hydroxytyrosol as a novel food pursuant to Regulation (EC) No 258/97 (full text). PMC.
• Auñón-Calles et al. (2013). Toxicological evaluation of pure hydroxytyrosol. Food and Chemical Toxicology. ScienceDirect.
• Application of Hydroxytyrosol in the Functional Foods Field: From Ingredient to Dietary Supplements. PMC.
• Novel Ingredients: Hydroxytyrosol as a Neuroprotective Agent; What Is New on the Horizon? PMC / Foods, 2025.
• Potential role of hydroxytyrosol in neuroprotection. Journal of Functional Foods, 2021. ScienceDirect.
• Effects of Hydroxytyrosol in Endothelial Functioning: A Comprehensive Review. PMC.
• Meta-analysis: The impact of oleuropein, hydroxytyrosol, and tyrosol on cardiometabolic risk factors. Critical Reviews in Food Science and Nutrition, 2025.
• Olive Tree Derivatives and Hydroxytyrosol: Their Potential Effects on Human Health and Its Use as Functional Ingredient in Meat. PMC.
• The EFSA Health Claim on Olive Oil Polyphenols: Acid Hydrolysis Validation and Total Hydroxytyrosol and Tyrosol Determination in Italian Virgin Olive Oils. PMC.
• Oleuropein, unexpected benefits! PMC / Oncotarget.
• Hydroxytyrosol supplementation improves antioxidant and anti-inflammatory status in individuals with overweight and prediabetes: A randomized, double-blind, placebo-controlled parallel trial. Clinical Nutrition, 2025. ScienceDirect.