About Herbs

Bottom Line: While extracts made from olive leaf have been shown to lower blood pressure, reduce cholesterol, and kill microorganisms in laboratories no studies have determined what effect olive leaf extracts will have in humans. Olive leaf extract has not been shown to have any effect on cancer.

Olive leaves contain a substance called oleuropein which is thought to be the mechanism by which olive leaf extracts (OLE) reduce cholesterol levels. When rats with high cholesterol were given oleuropein, their cholesterol levels fell. Rats given OLE, however, experienced greater cholesterol reduction than those given 10 times the amount of oleuropein. Because of this researches believe the oleuropein must work together with other substances contained within the leaf to reduce cholesterol levels. Within the body, oleuropein is converted into olenoic acid which may play a role in preventing viruses and bacteria from replicating within the body. Further laboratory studies have shown that OLE can relax arterial cells whether or not the arteries are covered by a thin layer of cells that normally control the pressure within the artery. Substances contained within the olive leaf have also been shown to affect the pathway in the body that maintains immune system regulated cell-death, however it is unclear what affect this has on the body. OLE reduces the level of glucose in the blood. OLE has also been found to kill a number of microorganisms including, yeasts, bacteria and fungi. Laboratory studies have also shown that OLE can influence proteins that prevent cell death that may prove effective against the Human Immunodeficiency Virus (HIV).

Limited studies of olive leaf extract on humans exist.

The pollen from olive tree can cause severe respiratory allergy⁽¹²⁾.

Olea Europaea

Drevied from the fresh or dried leaves of olive plant. The raw leaves or the extract have been used to treat infections, inflammation, diabetes, and hypertension. A major component of olive leaf, oleuropein, has been shown to have antioxidant properties ⁽¹⁾.  An animal study indicated that the hypoglycemic effect of olive leaf extract can induce insulin release and improve peripheral uptake of glucose⁽²⁾. Extracts of the leaf have strong antimicrobial properties ⁽³⁾ as well as potential anti-HIV properties ⁽⁴⁾. Other studies demonstrated antiarrhythmic, spasmolytic, diuretic ⁽⁵⁾, antihypertensive ⁽⁶⁾, and cholesterol lowering ⁽⁷⁾ properties in animals. The anticancer effect of olive leaf extract in humans is not known.

The cholesterol lowering effects of olive leaf extracts are thought to come from oleuropein, a substance contained within the leaf. Studies on hypercholesterolemic rats have shown that olive leaf extracts are more effective at lowering cholesterol than pure oleuropein. This implies that a synergistic effect occurs between oleuropein and another substance within the leaf ⁽⁷⁾. Oleuropein is converted into elenoic acid in the body which may prevent viruses and bacteria from replicating ⁽⁸⁾. The antihypertensive and vasodilating effects of olive leaf occurred independently of the integrity of the vascular endothelium ⁽⁹⁾. Constituents of olive leaf have been shown to strongly inhibit the complement system, although it is unknown what effect this has on the body ⁽¹⁰⁾. Hypoglycemic activities of olive leaf are attributed to two mechanisms: potentiation of glucose-induced insulin release and increased peripheral uptake of glucose. Hypoglycemic activity is greater in samples collected in the winter months ⁽²⁾. Olive leaf extract has been shown to be effective against the following microorganisms: E. coli, Pseudomonas aeruginosa, S. aureus, K. pneumoniae, Trichophyton mentagrophytes, Microsporum canis, T. rubrum and Candida albicans ⁽³⁾. Anti-HIV properties of Olive leaf extract include up-regulation of the expression of apoptosis inhibitor proteins as well as protein kinase signaling molecules ⁽⁴⁾. Few trials in humans are available in the current literature.

No severe adverse effect reported.

May affect blood glucose level.⁽¹¹⁾.