Olive (Olea europaea L.): A Comprehensive Reference
1. Identity
Botanical and Chemical Names
Olive (Olea europaea) is native to the Mediterranean region, and both the oil and the fruit are some of the main components of the Mediterranean diet. Several species within the olive family, botanically known as Olea europaea, provide commercial products such as food, lumber, cosmetics, and medicine. The tree belongs to the family Oleaceae. The common name "olive" is used to refer to the tree itself, its fruit (the drupe), the expressed oil, and increasingly the dried leaf used as a supplement.
Oleuropein is a glycosylated seco-iridoid, a bitter phenolic compound found in green olive skin, flesh, seeds, and leaves. The term oleuropein is derived from the botanical name of the olive tree, Olea europaea. Chemically, oleuropein is the ester of elenolic acid and 3,4-dihydroxyphenyl ethanol.
Natural Source and Parts Used
The olive tree, Olea europaea, is native to the Mediterranean basin and parts of Asia Minor. The fruit and compression-extracted oil have a wide range of therapeutic and culinary applications. Phenolic compounds are found in all parts of the olive plant, but their nature and concentration varies greatly between the various tissues. The commercially relevant parts are the fruit (drupes), the cold-pressed oil, and the leaves — all three of which are used in food, supplementation, and traditional medicine.
Common Forms and Preparations
- Extra-Virgin Olive Oil (EVOO): Cold-pressed oil from fresh olives, retaining the highest levels of phenolic compounds. Used as a culinary fat and in clinical studies as a dietary intervention.
- Virgin Olive Oil (VOO): Cold-pressed but with slightly less stringent quality criteria than EVOO; lower polyphenol content.
- Refined Olive Oil: Chemically or thermally refined; significantly reduced polyphenol content.
- Table Olives: Whole processed fruit, consumed as food. During processing of bitter and inedible green olives for consumption as table olives, oleuropein is removed from olives via a number of methods, including by immersion in lye.
- Olive Leaf Extract (OLE): Dried or liquid extract standardized to oleuropein and/or hydroxytyrosol content, available as capsules, tablets, tinctures, teas, and powders. It is available in various forms, including capsules, tinctures, powders, and teas.
2. Traditional and Historical Use
Ancient Origins
The olive was first cultivated around 5000 BCE, or even earlier, on the Carmel coast of ancient Israel. Here, simple olive presses have been excavated at the Neolithic site of Kfar Samir. Wild olives, which originated in Asia Minor, were collected by Neolithic people as early as the 8th millennium BC.
Olive trees and oil production in the Eastern Mediterranean can be traced to archives of the ancient city-state Ebla (2600–2240 BC), which were located on the outskirts of Aleppo. Dynastic Egyptians before 2000 BC imported olive oil from Crete, Syria, and Canaan, and oil was an important item of commerce and wealth. The Minoans used olive oil in religious ceremonies. The oil became a principal product of the Minoan civilization, where it is thought to have represented wealth.
Greece and Rome
Olives and olive oil were not only an important component of the ancient Mediterranean diet but also one of the most successful industries in antiquity. Cultivation of the olive spread with Phoenician and Greek colonization from Asia Minor to Iberia and North Africa and fine olive oil became a great trading commodity right through to the Roman period and beyond.
Besides food, olive oil has been used for religious rituals, medicines, as a fuel in oil lamps, soap-making, and skincare application. The Spartans and other Greeks used oil to rub themselves while exercising in the gymnasia. From its beginnings early in the 7th century BC, the cosmetic use of olive oil quickly spread to all of the Hellenic city-states, together with athletes training in the nude, and lasted close to a thousand years despite its great expense.
Biblical and Near Eastern Use
Olives and olive cultivation are mentioned extensively in ancient Roman agricultural texts, including those by Cato (De Agricultura, second century BCE) and Columella (De re rustica, first century CE), as well as in the Hebrew Mishna and Talmud (third century CE). The biblical text suggests ancient Israelites used olive oil in the ordination of high priests and kings (Exodus 30:33) and as fuel for lamps (Exodus 27:20, Leviticus 24:2). The olive also symbolized peace and prosperity in the Bible (Genesis 8:11, Deuteronomy 8:8), and victory and wisdom in ancient Greece.
Medicinal and Traditional Use
While its fruit and the oil derived from it are cornerstones of a healthy diet, the leaves of the olive tree have also been utilized for centuries in traditional and folk medicine practices. Historically, cultures from Egypt to Greece and Rome have employed olive leaf preparations to treat a variety of ailments, including fevers, infections, and wounds. Olive leaf tea and tinctures are commonly used as blood pressure-lowering and anti-inflammatory agents in Greece, Italy, Morocco, Palestine, Algeria, and East Africa.
3. Key Constituents and Active Compounds
Fatty Acid Fraction
Olive oil contains about 98% fatty acids, principally oleic acid, and 2% minor components of over 230 compounds such as squalene, tocopherols, sterols, and polyphenols. Extra-virgin olive oil contains about 55–83% oleic acid, and 3.5–21% linoleic acid. Oleic acid is a monounsaturated omega-9 fatty acid and is the single most abundant component of olive oil.
Phenolic Compounds
The main active constituents of olive oil include oleic acid, phenolic constituents, and squalene. The main phenolic compounds, hydroxytyrosol and oleuropein, give extra-virgin olive oil its bitter, pungent taste. Bioactive components of olive oil include oleic acid, tyrosol, hydroxytyrosol, linoleic acid, oleuropein, oleanolic acid, maslinic acid, and melatonin.
Oleuropein is the main glycoside in olives and is responsible for the bitter taste of immature and unprocessed olives. During maturation of fruit or as a result of olive processing (such as oil production), chemical and enzyme reactions occur which reduce the concentration of oleuropein and raise the concentration of hydroxytyrosol, which is the principal degradation product of oleuropein.
The green olive drupes are rich in biophenol secoiridoids such as oleuropein, demethyloleuropein, ligstroside, and their hydrolytic derivatives such as oleuropein aglycone, elenolate, oleoside-11-methyl ester, elenoic acid, hydroxytyrosol, and tyrosol. Oleocanthal and oleacein present in virgin olive oil are dialdehydic isomeric forms of ligstroside and oleuropein aglycones, respectively.
Olive oil contains numerous polyphenols, among which are elenolic acid and alpha-tocopherol, a vitamin E compound. Oleuropein, together with other closely related compounds such as 10-hydroxyoleuropein, ligstroside and 10-hydroxyligstroside, are tyrosol esters of elenolic acid. Other phenolic constituents include flavonoids, lignans, and pinoresinol.
The primary constituents which are believed to contribute to the health benefits of olive leaves are oleuropein and hydroxytyrosol, as well as several other flavonoids, such as verbascoside, apigenin-7-glucoside, and luteolin-7-glucoside.
Oleocanthal
Oleocanthal is a phenylethanoid, or a type of natural phenolic compound found in extra-virgin olive oil. It appears to be responsible for the burning sensation that occurs in the back of the throat when consuming such oil. Oleocanthal is a tyrosol ester and its chemical structure is related to oleuropein, also found in olive oil. The concentration of oleocanthal in EVOO is variable, ranging from as little as 0.2 mg/kg to 498 mg/kg.
Other Minor Compounds
In a reference amount of 100 grams of olive oil, it supplies 884 kcals of food energy, and is a rich source of vitamin E (96% DV) and vitamin K (50% DV). The oil also contains squalene — a triterpene hydrocarbon — as well as beta-sitosterol, campesterol, and other phytosterols.
4. Established Mechanisms of Action
Antioxidant Activity
The main phenolics — hydroxytyrosol, tyrosol, and oleuropein — occur in highest levels in virgin olive oil and have demonstrated antioxidant activity. Antioxidants are believed to be responsible for a number of olive oil's biological activities. Polyphenols act as antioxidants both to preserve the oil from oxidation and to benefit health when ingested. Oleuropein, the major constituent of olive leaves, has been shown to be a potent antioxidant. Its radical scavenging activity has been well documented.
COX Enzyme Inhibition (Oleocanthal)
In 2005, Monell researchers and collaborators announced the discovery that oleocanthal is a non-steroidal, anti-inflammatory agent that inhibits activity of cyclooxygenase (COX) enzymes. Ibuprofen is an inhibitor of the cyclooxygenase enzymes COX-1 and COX-2, which catalyse steps in the biochemical inflammation pathways derived from arachidonic acid to pro-inflammatory prostaglandins [PGE2]. Oleocanthal, like ibuprofen, caused dose-dependent inhibition of COX-1 and COX-2 activities with reduced pro-inflammatory prostaglandin-biosynthesis [PGE2].
Research shows that at the same concentration, oleocanthal inhibits COX-1 and COX-2 more effectively than ibuprofen. At 25 micromolar, oleocanthal inhibits COX activity by 41 to 57%, while ibuprofen at the same concentration inhibits it by only 13 to 18%. The current study identified TRPA1 as the receptor that is activated by both oleocanthal and ibuprofen, and the findings establish that oleocanthal causes the distinctive sting of olive oil through its activation of TRPA1. These findings were largely established in vitro; the clinical relevance at dietary doses remains under investigation.
Endothelial and Vascular Effects
In humans, oleuropein has been shown to reduce the vascular stiffness index, indicating beneficial effects on arterial elasticity and vascular function. It increased eNOS activity by restoring aortic eNOS phosphorylation, though this finding derives primarily from preclinical models.
LDL Oxidation Protection
The polyphenols present in olive oil have received increasing scientific attention, particularly since the European Food Safety Authority (EFSA) approved the health claim that "olive oil polyphenols help to protect low-density lipoproteins (LDL) from oxidative damage," an effect attributed to their antioxidant activity. Oleuropein has been shown to inhibit the oxidation of low-density lipoproteins in vitro and in vivo.
Insulin Signaling
Key bioactive components of olive oil, such as oleic acid and phenolic compounds, were identified as modulators of insulin signaling. These compounds enhanced the insulin signaling pathway, improved lipid metabolism, and reduced oxidative stress by decreasing reactive oxygen species (ROS) production.
5. Scientific Evidence by Area of Use
5.1 Cardiovascular Health
The strongest body of human evidence for olive oil concerns cardiovascular risk reduction, most prominently established through the PREDIMED trial.
The PREDIMED study was a multicenter randomized primary CVD prevention trial conducted in Spain in 7,447 participants between 55 and 80 years of age, without prevalent CVD at the time of recruitment but at high CVD risk. Participants were randomized to one of the following three dietary interventions: a Mediterranean diet supplemented with extra-virgin olive oil (MedDiet with EVOO), a Mediterranean diet supplemented with nuts (MedDiet with nuts), or a control diet consisting of advice to follow a low-fat diet. Recruitment began in June 2003 and concluded in June 2009.
On June 13, 2018, the New England Journal of Medicine (NEJM) retracted the 2013 PREDIMED study as a result of error in randomization procedures affecting a portion of participants. Despite these revelations, there was no significant change in the results of the trial when researchers reanalyzed the data: in both the original and republished study, the incidence of cardiovascular disease in the Mediterranean diet groups was lowered by approximately 30% when compared to the control diet.
An observational analysis of the PREDIMED population examined olive oil intake specifically. The analysis included 7,216 men and women at high cardiovascular risk, aged 55 to 80 years. Participants were randomized to one of three interventions: Mediterranean Diets supplemented with nuts or extra-virgin olive oil, or a control low-fat diet. The analysis was conducted as an observational prospective cohort study. The median follow-up was 4.8 years. For each 10 g/day increase in extra-virgin olive oil consumption, cardiovascular disease and mortality risk decreased by 10% and 7%, respectively. No significant associations were found for cancer and all-cause mortality. The associations between cardiovascular events and extra-virgin olive oil intake were significant in the Mediterranean diet intervention groups and not in the control group. Olive oil consumption, specifically the extra-virgin variety, is associated with reduced risks of cardiovascular disease and mortality in individuals at high cardiovascular risk.
Strength of evidence: Moderate-to-strong for cardiovascular benefit from EVOO within a Mediterranean dietary context. The PREDIMED reanalysis preserved the core findings, but the co-dietary confounders (nuts, whole diet pattern) make it difficult to isolate EVOO's independent contribution.
5.2 Blood Pressure (Olive Leaf Extract)
A randomised, double-blind, controlled, crossover trial investigated the effects of a phenolic-rich olive leaf extract (OLE) on blood pressure. A total of 60 pre-hypertensive males consumed either OLE (136 mg oleuropein; 6 mg hydroxytyrosol) or a polyphenol-free control daily for 6 weeks before switching to the alternate arm after a 4-week washout. Daytime systolic blood pressure (−3.95 mmHg, p=0.027) and 24-h systolic blood pressure (−3.33 mmHg, p=0.045) and daytime and 24-h diastolic blood pressure were all significantly lower following OLE intake, relative to the control.
Reductions in plasma total cholesterol (−0.32 mmol/L, p=0.002), LDL cholesterol (−0.19 mmol/L, p=0.017) and triglycerides (−0.18 mmol/L, p=0.008) were also induced by OLE compared to control.
A 2022 systematic review and meta-analysis synthesized this evidence. Twelve studies (n = 819 participants) were included. Overall analyses showed that OLE supplementation significantly decreased triglyceride levels (WMD = −9.51 mg/dL, 95% CI −17.83, −1.18; P=0.025) and systolic blood pressure (WMD = −3.86 mmHg, 95% CI −6.44, −1.28 mmHg; P=0.003).
Olive leaf extract can decrease 24-hour blood pressure, blood pressure load, and diastolic blood pressure variability with improvement of lipid profile, systemic inflammation, and body weight in hypertensive patients.
Strength of evidence: Moderate. Multiple small-to-medium RCTs show consistent, modest reductions in blood pressure (systolic reductions in the range of 3–4 mmHg) in pre-hypertensive and hypertensive populations. Larger, longer-duration trials are still needed.
Note on EFSA: "When put to the test under the highest scientific standards, there is still not enough human evidence to confirm a cause-and-effect relationship for lowering LDL-cholesterol or systolic blood pressure," as noted in commentary following EFSA's 2025 scrutiny of olive oil polyphenol health claims. None of the trials presented lasted at least eight weeks, which EFSA considers the minimum duration necessary to demonstrate stable effects on blood lipids or blood pressure.
5.3 Lipid Profile
OLE has been reported to lower systolic blood pressure and diastolic blood pressure from baseline in both hypertensive and pre-hypertensive individuals, and to improve plasma lipid profiles in both normo-lipidaemic and hypercholesterolaemic subjects.
In a study of 20 monozygotic twin pairs, a 200 mg/day intake of oleuropein resulted in a 0.6 mmol/L decrease in total cholesterol, a 0.4 mmol/L decrease in LDL cholesterol, and no change in triglycerides relative to healthy lifestyle advice alone after 8 weeks; a 100 mg/day dose had no significant effects on lipids. A more recent study reported decreases of 0.68, 0.90 and 0.047 mmol/L in total cholesterol, LDL-C and triglycerides, respectively, after 12 months of consumption of a supplement containing 100 mg oleuropein.
Virgin and extra-virgin olive oils contain a specific fraction of polyphenols (hydroxytyrosol and its derivatives) that produce beneficial physiological effects. The European Food Safety Authority (EFSA) authorized a health claim for olive oil containing at least 250 mg/kg of those polyphenols.
Strength of evidence: Moderate for LDL protection from oxidation (EFSA-approved claim). Evidence for LDL-lowering per se is inconsistent across studies and has not yet met EFSA's threshold for a cause-and-effect claim.
5.4 Glucose Metabolism and Diabetes
In a meta-analysis of 51 randomized controlled trials (n = 4,334 participants), olive oil consumption by adults does not significantly affect overall glycemic control. However, a daily dose of 25–50 g significantly improves the HOMA-IR parameter, suggesting a potential benefit for diabetes management. These findings highlight the need for further research to fully understand the practical implications of olive oil consumption in diabetes care.
Four cohort studies including 15,784 type 2 diabetes cases and 29 trials were included in a systematic review and meta-analysis. The highest olive oil intake category showed a 16% reduced risk of type 2 diabetes (RR: 0.84; 95% CI: 0.77, 0.92) compared with the lowest.
Regarding olive leaf extract specifically, laboratory studies suggest that olive leaf extract may improve glycaemic control; however, clinical studies in persons with diabetes are lacking. The pilot ESOLED randomized controlled trial (31 participants, 24 weeks) found that the trial was inconclusive in determining whether OLE is effective at improving glycaemic control, insulin sensitivity, diabetes-related distress, and quality of life, and larger trials and further exploration of the bioavailability of OLE are needed to fully assess the therapeutic potential of OLE in diabetes.
As potential mechanisms of action, reductions in glycemic load (especially when replacing carbohydrates with MUFA) and the consecutive attenuation in insulin secretion as well as increased insulin sensitivity may explain the beneficial effects of MUFA on glycemic control. Although there is some evidence of a beneficial effect of plant-based monounsaturated fatty acids, it is still not clear whether these effects are due to phenolic compounds of extra-virgin olive oil or the fatty acid composition.
Strength of evidence: Weak-to-moderate. Observational data suggest reduced T2D risk; intervention data on glycemic control are inconsistent, and olive-leaf-specific human clinical evidence in diabetic populations remains very limited.
5.5 Anti-Inflammatory Effects
The anti-inflammatory activity of olive constituents is among the best-characterized at the mechanistic level. In a landmark study, oleocanthal (OLC), a major phenolic in extra-virgin olive oil, was found to possess anti-inflammatory activity similar to ibuprofen, involving inhibition of cyclooxygenase (COX) enzymes. 50 g (more than three and a half tablespoons) of a typical extra-virgin olive oil per day contains an amount of oleocanthal with similar in vitro anti-inflammatory effect as 1/10 of the adult ibuprofen dose.
Oleuropein and its principal metabolite, hydroxytyrosol, exhibit antioxidant, anti-hypertensive, anti-atherosclerotic, and anti-inflammatory effects in preclinical studies. Translation of these findings to clinically significant anti-inflammatory benefit in humans at dietary doses remains preliminary.
Strength of evidence: Preliminary. The COX-inhibitory mechanism of oleocanthal is established in vitro. Clinical evidence for meaningful anti-inflammatory effects from dietary olive oil consumption at achievable doses is still emerging.
5.6 Neuroprotection and Cognitive Function
Evidence in modern studies relating to neurological and age-related health on olive biophenols (oleuropein, hydroxytyrosol, oleuropein aglycone, and oleocanthal) has demonstrated neuroprotection and cognitive support: antioxidant, anti-inflammatory, anti-amyloidogenic, anti-tau, and neuroprotective effects in animal models of Alzheimer's disease (AD), Parkinson's disease (PD), stroke, multiple sclerosis, depression, and anxiety.
Oleuropein-based studies reported inhibition of amyloid-β and α-synuclein aggregation with behavioural improvements. Hydroxytyrosol primarily exerted antioxidant and anti-inflammatory effects with modest cognitive benefits. Oleocanthal showed the most consistent anti-amyloid and anti-tau activity, including enhanced amyloid-β clearance across the blood–brain barrier.
Most studies show a moderate risk of bias due to incomplete reporting, randomisation and blinding. Olive biophenols demonstrate consistent neuroprotective effects in preclinical models; however, translation to clinical application remains limited by pharmacokinetic constraints and methodological heterogeneity.
Strength of evidence: Weak in humans. The neuroprotective evidence base is predominantly preclinical (animal and cell studies). Human clinical trials in this area are sparse and have not yet established efficacy.
5.7 Anticancer Properties
Both inflammatory and cancer cell models have shown that olive leaf polyphenols are anti-inflammatory and protect against DNA damage initiated by free radicals. The various bioactive properties of olive leaf polyphenols are a plausible explanation for the inhibition of progression and development of cancers. The pathways and signaling cascades manipulated include the NF-κB inflammatory response and the oxidative stress response.
Evidence for the protective effect of olive polyphenols for cancer in humans remains anecdotal and clinical trials are required to substantiate these claims.
Strength of evidence: Very weak in humans. Anticancer findings are largely confined to in vitro (cell culture) and animal studies. No human clinical trials have established a causal anti-cancer effect of olive-derived compounds.
6. Body Systems and Health Areas
- Cardiovascular system: Blood pressure regulation, LDL oxidation protection, lipid profile improvement, reduction of cardiovascular event risk.
- Metabolic system: Insulin sensitivity, glucose metabolism, possible reduction in type 2 diabetes risk.
- Inflammatory pathways: COX-1 and COX-2 inhibition by oleocanthal; NF-κB pathway modulation by oleuropein.
- Nervous system: Preliminary neuroprotective activity in preclinical models; anti-amyloid and anti-tau actions.
- Immune and oncological: In vitro antimicrobial and anticancer properties; no clinical translation confirmed.
- Skin: Topical use as emollient; historically applied to wounds and skin conditions.
7. Dosage Forms and Reported Study Dosages
Olive Oil (Dietary)
The PREDIMED study used a Mediterranean diet supplemented with extra-virgin olive oil at least 4 tablespoons (approximately 60 mL) per day.
A meta-analysis of 51 RCTs found that olive oil consumption overall does not significantly affect glycemic control, but a daily dose of 25–50 g significantly improves the HOMA-IR parameter.
Olive Leaf Extract (Supplement)
The standard supplemental dose reported in clinical studies is 100–136 mg of oleuropein per day, which corresponds to approximately 250–500 mg of extract standardized to 20–40% oleuropein. Most clinical trials have divided the daily dose into two administrations (e.g., twice daily with meals), though some have used a single daily dose. It is not clear whether divided dosing is superior.
One clinical trial in patients with stage 1 hypertension used an olive leaf extract dosage of 500 mg twice daily for 8 weeks. Supplementation with olive leaf extract equating to a daily dose of oleuropein 51.1 mg and hydroxytyrosol 9.7 mg for 12 weeks was examined in a crossover study evaluating effects on insulin action and cardiovascular risk factors in men.
In a twin-pair study, 200 mg/day of oleuropein over 8 weeks produced significant reductions in total cholesterol and LDL, while a 100 mg/day dose had no significant effects on lipids.
Clinical trials have ranged in duration from 6 weeks to 12 months. Clinical trials have used various extracts providing 100 to 136.2 mg oleuropein daily from products standardized to about 1% to 40% oleuropein. To get a dose of 100 mg of oleuropein, one would need 250 mg of a 40% extract, 500 mg of a 20% extract, or 1,000 mg of a 1% extract. The higher the percentage of oleuropein, the less extract required.
EFSA Polyphenol Benchmark
Virgin and extra-virgin olive oils contain hydroxytyrosol and its derivatives that produce beneficial physiological effects. EFSA authorized a health claim for olive oil containing at least 250 mg/kg of those polyphenols, specifically for the protection of LDL particles from oxidative damage.
8. Safety Considerations and Interactions
General Safety
Olive leaf extract appears to be generally safe and well-tolerated based on small clinical trials, although gastrointestinal symptoms can occur. Olive oil itself consumed at dietary levels has a very long and extensive safety record in Mediterranean populations.
Hypotension
Olive leaf may enhance the hypotensive effect of blood pressure–lowering agents or other herbal products with blood pressure–lowering effects. Rare instances of hypotension (excessively low blood pressure) have been associated with high doses exceeding 2,000 mg per day, particularly in individuals predisposed to low blood pressure. Given the blood pressure-lowering effects of olive leaf extract, individuals who already have low blood pressure or who are taking antihypertensive medications should exercise caution and monitor for symptoms of hypotension.
Blood Sugar Medications
Olive leaf extract should be used with caution in people with hypoglycemia, diabetes, or those taking blood sugar-lowering medications.
Anticoagulants and NSAIDs
Hydroxytyrosol's anti-inflammatory effects may theoretically enhance or interact with NSAID medications and anticoagulants. This is a theoretical concern based on mechanism; no serious interactions have been confirmed in clinical trials to date.
Pregnancy and Lactation
There is insufficient safety data for olive leaf extract use during pregnancy and breastfeeding. No specific uterotonic effects have been documented in human studies, but caution is advised due to the lack of data.
Allergy
Allergic reactions can occur, particularly among people who are sensitive or allergic to olive pollen or the pollen of related plants.
Bioavailability Note
EFSA has approved a health claim for the protection of LDL particles from oxidative damage only when hydroxytyrosol is consumed within EVOO, which limits its direct use in supplements or functional foods. The health effects of isolated hydroxytyrosol remain less well understood, particularly since the EFSA health claim applies only when these phenols are consumed within the EVOO matrix.
References
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