Oleuropein is the bitter phenolic compound that dominates the olive leaf and the unripe olive fruit. It is the reason a fresh olive cannot be eaten straight from the tree. During milling and digestion it breaks down into smaller compounds, including hydroxytyrosol. In laboratory and early human studies it is associated with antioxidant activity and healthy blood pressure and lipid levels.

What is oleuropein?

Oleuropein is a secoiridoid, a class of compound found only in the olive family. Structurally it is a glycoside. That means it has three parts joined together: a hydroxytyrosol unit, a secoiridoid unit called elenolic acid, and a glucose sugar.

The olive tree makes oleuropein as a defence against insects and microbes. Levels are highest in the leaves and in young green fruit. As the olive ripens and darkens, oleuropein falls steeply. This is one reason early harvest oils carry more phenolic compounds than late harvest ones.

Its sensory signature is bitterness. Table olives are cured in brine or lye precisely to break oleuropein down so the fruit becomes edible. In a fresh oil, a clean bitter note on the tongue points to oleuropein-derived compounds.

How it works in the body

Oleuropein itself is water-loving and only partly absorbed. Much of its activity comes from what it becomes. When olives are crushed, enzymes in the fruit strip off the sugar. This produces oleuropein aglycone and oleacein, which dissolve into the oil. In the gut, further breakdown releases hydroxytyrosol, one of the best-absorbed olive phenols.

In laboratory studies, oleuropein and its breakdown products neutralise free radicals and protect fats from oxidation. They also reduce signals from inflammatory pathways such as NF-kB in cell models. In olive leaf research, interest centres on blood vessel tone, blood pressure and blood lipids. These findings are promising but still developing in humans.

What the research shows

Olive leaf extract and blood pressure. In a randomised, placebo-controlled crossover trial, men with mildly raised blood pressure took a phenolic-rich olive leaf extract for six weeks (Lockyer et al., European Journal of Nutrition, 2017). The extract supplied oleuropein and hydroxytyrosol. Blood pressure and some blood lipids were lower than with placebo. The trial was small, and larger studies are needed.

The EU health claim. The authorised EU claim for olive oil polyphenols counts hydroxytyrosol and its derivatives, and the regulation names the "oleuropein complex" as one of them (Commission Regulation (EU) No 432/2012). So oleuropein-derived compounds are part of the measured total behind the claim that olive oil polyphenols protect blood lipids from oxidative stress.

A broad pharmacology review. A review of laboratory and animal work describes antioxidant, anti-inflammatory, antimicrobial and blood-vessel-related effects for oleuropein (Omar, Scientia Pharmaceutica, 2010). Most of this evidence is preclinical. It explains why the compound is studied, not what it does in people.

Cancer and metabolic models. Cell and animal studies have reported that oleuropein slows the growth of some cancer cell lines and improves markers of glucose handling (preclinical). These are early findings and are not evidence of any treatment effect.

How much is in olive oil and in Phenolia

Intact oleuropein is plentiful in leaves and green fruit but scarce in finished oil. Being water-loving, most of it stays in the water and pulp during milling. What reaches the oil is mainly its fat-soluble breakdown products, oleuropein aglycone and oleacein. In fresh, early harvest oils these can add up to tens or even hundreds of mg/kg.

The olive leaf is a different matter. Dried leaf is one of the richest natural sources of oleuropein, which is why leaf extracts are often standardised to it. That gives a capsule a way to provide oleuropein that liquid oil cannot.

Harvest timing and cultivar still matter. Green Koroneiki olives, the Greek variety Pomoni uses, are known for high secoiridoid content. Cold, quick extraction preserves more of it.

Pomoni measures each compound by HPLC (high-performance liquid chromatography), which separates oleuropein from its relatives before measuring. Pomoni High-Phenolic Olive Oil provides the oil-soluble forms. Phenolia Daily adds olive leaf extract alongside high-phenolic olive oil (powdered) and Greek Mountain Tea. The current batch certificate on testing and certifications lists the measured figures. Our olive oil polyphenols science guide covers the wider family.

Related compounds

• Hydroxytyrosol
• Oleacein
• Oleocanthal
• Tyrosol
• The science of polyphenols
• HPLC vs NMR testing

Frequently asked questions

These statements have not been evaluated by the Food and Drug Administration. Pomoni products are not intended to diagnose, treat, cure or prevent any disease.

Sources

1. Lockyer S, Rowland I, Spencer JPE, Yaqoob P, Stonehouse W. Impact of phenolic-rich olive leaf extract on blood pressure, plasma lipids and inflammatory markers: a randomised controlled trial. European Journal of Nutrition. 2017;56(4):1421-1432. doi:10.1007/s00394-016-1188-y
2. Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods. Official Journal of the European Union. 2012. eur-lex.europa.eu
3. Omar SH. Oleuropein in olive and its pharmacological effects. Scientia Pharmaceutica. 2010;78(2):133-154. doi:10.3797/scipharm.0912-18