The leaf of the olive tree, Olea europaea, has a long history of use in traditional practices, especially in Mediterranean cultures. While the olive fruit and its oil are well-known, the leaves have also been used for centuries. Recent scientific interest has focused on understanding the leaf’s chemical composition and the properties of its compounds, shifting from historical use to modern investigation.
Key Bioactive Compounds in Olive Leaves
The primary reason for the scientific focus on olive leaves lies in their rich concentration of plant-based compounds known as polyphenols. Among these, a secoiridoid named oleuropein is the most abundant constituent. In its fresh state, an olive leaf can contain oleuropein in concentrations ranging from 6% to 9% of its dry weight. This compound is responsible for the distinctively bitter taste associated with the leaves and unprocessed olives. Oleuropein is an ester formed by elenolic acid and another phenol, hydroxytyrosol.
Another compound in olive leaves is hydroxytyrosol. While present in smaller amounts than oleuropein in the raw leaf, its concentration increases as oleuropein breaks down. Oleuropein and hydroxytyrosol are considered the primary drivers of the leaf’s biochemical characteristics. The leaves also contain other compounds, such as flavonoids and triterpenoids, that add to its complex chemical makeup.
The concentration of these bioactive compounds is not static. It is influenced by factors like the olive tree cultivar, harvest time, and processing methods used after collection. For instance, certain drying methods can preserve or degrade these heat-sensitive compounds, altering the final chemical profile of a commercial olive leaf product.
Reported Biological Activities
Research has identified several biological activities of olive leaf compounds, primarily in laboratory settings. The polyphenols, especially oleuropein and hydroxytyrosol, have antioxidant properties. Antioxidants neutralize unstable molecules called free radicals, which cause cellular damage through oxidative stress. Studies show that olive leaf extracts can scavenge these free radicals, suggesting a protective effect.
These compounds have also been studied for their anti-inflammatory effects. While inflammation is a natural response, chronic inflammation is linked to various health conditions. In laboratory models, oleuropein has been shown to inhibit the production of certain inflammatory mediators, like leukotriene B4. This suggests a mechanism by which olive leaf constituents might help modulate inflammatory processes.
The antimicrobial potential of olive leaf components has also been an area of investigation. Studies have shown that oleuropein and its derivatives exhibit activity against a range of microorganisms, including certain bacteria and fungi. The proposed mechanism involves the disruption of microbial processes, although the exact interactions are complex. This activity has been observed in controlled lab environments and forms the basis for its traditional use in some cultures.
Research has also explored the effects of olive leaf extract on cardiovascular health markers. Some human trials suggest that supplementation may influence blood pressure. One study found that a daily intake of 500 mg of olive leaf extract twice a day lowered blood pressure in individuals with stage 1 hypertension after eight weeks. Other studies have examined its effect on cholesterol, with some results indicating a reduction in low-density lipoprotein (LDL) cholesterol.
Forms and Common Preparations
The most traditional preparation is a tea made from dried, whole, or cut leaves. This involves steeping the leaves in hot water to release their water-soluble compounds. The concentration of active compounds in the tea can vary depending on the quantity of leaves used and the steeping time.
A more concentrated form is the liquid extract or tincture. These preparations are created by soaking the leaves in a solvent, such as alcohol or glycerin, to pull out a broader spectrum of compounds than water alone. Liquid extracts offer the advantage of higher bioavailability and quicker absorption compared to solid forms. They are sold in dropper bottles, allowing for flexible administration by adding the liquid to water or another beverage.
The most common form in the commercial supplement market is encapsulated powder. This involves drying and milling the leaves into a fine powder, which is then placed into gelatin or vegetable-based capsules. This method provides a convenient, pre-measured dose and avoids the bitter taste of the raw leaf and its extracts. The powders can vary in concentration, with some products standardized to contain a specific percentage of oleuropein to ensure consistent potency.
Considerations for Use
While olive leaf is considered safe for most people, some may experience mild side effects like stomach discomfort, headaches, or coughing. People with an allergy to olive tree pollen may also have an allergic reaction to olive leaf extract.
A primary consideration involves potential interactions with prescription medications. Because olive leaf extract may lower blood pressure and blood sugar, it can enhance the effects of drugs for these conditions. Combining them could cause blood pressure or blood sugar to drop to unsafe levels, so individuals taking antihypertensive or diabetes medications should exercise caution.
Some evidence suggests olive leaf extract may have a mild blood-thinning effect by preventing platelets from sticking together. This could increase the effect of anticoagulant and antiplatelet drugs, such as warfarin. Due to these possible interactions, it is recommended to consult with a healthcare provider before starting any new supplement regimen, especially for those with pre-existing health conditions or taking other medications.