Pharmacological Effect Of Olive Leaves
Dr. Anargyros N. Moulas, Assistant Professor at TEI Larisas – Department of Animal Production, Laboratory of Agricultural Chemistry: The olive tree (Olea Europaea) is a species endemic to the broader Mediterranean region since the Tertiary period.
The olive plant is minimally demanding and highly durable in all conditions.
The leaves, fruit and oil of the olive tree have an important place in agriculture, nutrition and traditional pharmacopoeia and medicine of many countries, mainly in the Mediterranean.
The first olive cultivators are believed to be the Phoenicians. Ancient Egyptians used it as medicine and also for embalming the dead. In the Old Testament (Genesis 8:11), the dove brought to Noah an olive stick after the cataclysm as a symbol of the cataclysm’s end. The leaves of the olive tree have been used in traditional medicine as antihypertensives, as vasodilators, as anti-‐rheumatics, diuretics, antipyretics and hypoglycaemics. Modern pharmacological studies have shown its anticholesterolemic, vasodilative, hypotensive and antimicrobial effect, while new effects are under study. Several phenolic compounds and derivatives are contained in olive leaves but also in its fruit and oil. Most important of these compounds is oleuropein and hydroxytyrosol (3,4-‐dihydroxy-‐phenylethanol).
Isolated in the extract of olive leaves, among others, 3,4-‐dihydroxyphenylesters and flavonoid glycosides mainly of rutin and luteolin have been found. The properties of olive tree leaves have been attributed primarily to the iridoids of the olive leaf and specifically the secoiridoid oleuropein and hydroxytyrosol [1,2].
Oleuropein exists also in the olive fruit, it is the bitter substance that is neutralized by the processing of the olive fruit. These two substances are known for their antioxidant properties  and are considered to give the olive tree resistance against damage from insects and bacteria. The total extract of olive leaves, however, shows a higher antioxidant effect than these two ingredients . Several ingredients of the olive leaf, and especially oleuropein, tyrosol, hydroxytyrosol and their esters as well as certain phenolic acids such as caffeic and vanillic, are also present in the fruit and oil of the olive .
The first official report on the use of olive leaves in medicine dates back to 1854, when Hanbury mentioned in the Pharmaceutical Journal a simple prescription for the use of the aqueous extract of olive leaves as an antipyretic. Since the early 20th century there are reports in literature on the composition and effect of olive leaves .
Specifically mentioned are the antioxidant [1,2,3], antimicrobial [1,6], antihypertensive [1,4,7,8] vasodilatory  and hypoglycemic  effects of the leaf extract or its individual components. The extract of olive leaves and oleuropein itself has been found to have potent bactericidal effect in vitro [1, 6]. Specifically, the extract has been found to be effective against many pathogens including influenza viruses, herpes, fungi and bacteria. However, its effectiveness in vivo has not been sufficiently proven. Also found is the anticomplementary effect of some flavonoids in the olive leaf such as apigenin and luteolin .
The olive leaves, in the form of an extract, have also been used in traditional medicine as antineoplastics. This effect of olive leaves has lately been a subject of research , by our research group, among others. Clinical data on the use of olive leaves in the treatment of hypertension, have been around since the 1950s . The effect of the minor components, mainly flavonoids of the olive tree, on cardiovascular diseases has been recently reviewed . Incubation of LDL cholesterol with oleuropein and hydroxytyrosol has been found to reduce the loss of vitamin E after the addition of CuSO4 and to inhibit the formation of lipid hyperoxidation such as isoprostanes, lippperoxides and malondialdehyde. Other effects of olive leaf polyphenols include inhibition of blood platelet aggregation, reduced production of eicosenoic acid from activated leukocytes and increased production of nitric oxide (NO) by murine macrophages after the effect of endotoxin. The first effects likely influence the formation of blood clots and inflammation while the latter is likely to play a role in the protection against parasites .
Not yet resolved is the question of whether flavonoids and polyphenols are absorbed from the diet and if they have these effects in vivo, although for the first issue, recently, a dose-‐dependent absorption has been found. The experimental data shows that the phenols present in the olive plant reduce the oxidation of LDL cholesterol in laboratory animals .
In studies conducted on rats it has been found that the extract of olive leaves has a hypoglycemic and antidiabetic effect on rats with diabetes induced by alloxan [1,10].
The effect was different depending on the season the leaves were gathered, with maximum effect during the winter period and especially in February . Already in the U.S. market, and also on the Internet, olive leaf extracts as food supplements in tablet form are available from various companies. Their recommended use is as an antimicrobial and immune system booster. In particular the consumption of the olive leaf extract is recommended for the strengthening of the immune system or as a natural antimicrobial for fungal and viral infections such as influenza and herpes and, lastly, it is recommended for chronic fatigue. The olive leaves constitute a unique source for receiving active ingredients with pharmaceutical effect. Some of these substances, such as oleuropein and hydroxytyrosol, are present in lesser quantities in olive oil, which however, due to its nutritional and economic value, is not suitable for receiving substances. The first indications for the possible use of the components of olive leaves for medicinal purposes are very encouraging.