Olive leaf is the leaf of the olive tree (Olea europaea). Although olive oil is well known for its flavor and health benefits, the leaf has been used medicinally in various times and places. Olive leaf and olive leaf extracts (OLE), are now marketed as anti-aging, immunostimulator, antioxidant, anti-inflammatory and antibiotic agents. Though there is some laboratory evidence for these effects in biological standardization experiments (i.e., bioassays), clinical evidence in humans is inconclusive.
Clinical evidence has been conflicting regarding any blood pressure lowering effect of carefully extracted olive leaf extracts. Bioassays support its antibacterial, antifungal, and anti-inflammatory effects at a laboratory level. A liquid extract made directly from fresh olive leaves gained international attention when it was shown to have an antioxidant capacity almost double green tea extract and 400% higher than vitamin C.
The silvery green leaves are oblong, measuring 4–10 centimetres (1.6–3.9 in) long and 1–3 centimetres (0.39–1.2 in) wide.
The primary active compounds in unprocessed olive leaf are believed to be the antioxidants oleuropein and hydroxytyrosol, as well as several other polyphenols and flavonoids, including oleocanthal. Elenolic acid is a component of olive oil and olive leaf extract. It can be considered as a marker for maturation of olives. Oleuropein, together with other closely related compounds such as 10-hydroxyoleuropein, ligstroside and 10-hydroxyligstroside, are tyrosol esters of elenolic acid.
Nutritional and medicinal uses
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Researchers have found that olive leaf dilates isolated rat aorta. A study conducted on monozygotic borderline hypertensive twins showed significant reduction of blood pressure in a dose-related manner.
Recent research in rodents has shown that olive leaf extracts (OLE) may reduce infarct volume, brain edema, as well as improve blood–brain barrier permeability and neurological deficit scores after transient middle cerebral artery occlusion (stroke). Furthermore, olive leaf extracts attenuate acetic acid-provoked chronic intestinal inflammation probably through the antioxidant and anti-inflammatory effects of polyphenols such as oleuropein and hydroxytyrosol. 
Olive leaf harbours antioxidant properties that help protect the body from the continuous activity of free radicals. Free radicals are highly reactive chemical substances that can cause cellular damage if left unchecked. Some recent research on the olive leaf has shown its antioxidants to be effective in treating some tumors and cancers such as liver, prostate, colon, skin and breast cancer, clinical studies lacking; Olive leaf is especially potent when used in combination with other antioxidants.
A randomized controlled double-blind crossover trial in New Zealand found that olive leaf extract capsules significantly improved insulin sensitivity and pancreatic β-cell responsiveness in middle-aged overweight men.
Olive leaf can be taken as a liquid concentrate, dried leaf tea, powder, or capsule. The leaf extract can be taken in powder, liquid concentrate, or capsule form.
Soaps and cosmetics
Olive leaf extracts are sometimes used in skin creams and other cosmetics for application to the skin or other body surfaces. Olive leaf extract has been shown to provide antioxidant and antibacterial effects that can prolong the shelf life of cosmetic preparations. 
- Kilham, Chris, Healing Power of Olive Leaf, January 23, 2013, FoxNews.com
- Perrinjaquet-Moccetti et al. Food Supplementation with an Olive (Olea europaea L.) Leaf Extract Reduces Blood Pressure in Borderline Hypertensive Monozygotic Twins, 2008.
- Somova et al. Antihypertensive, antiatherosclerotic and antioxidant activity of triterpenoids isolated from Olea europaea, subspecies africana leaves, 2003.
- Khayyal et al. Blood pressure lowering effect of an olive leaf extract (Olea europaea) in L-NAME induced hypertension in rats, 2002.
- Zarzuelo et al. Vasodilator effect of olive leaf, 1991.
- Perrinjaquet-Moccetti, Tania; Busjahn, Andreas; Schmidlin, Caesar; Schmidt, Annette; Bradl, Barbara; Aydogan, Cem (September 2008). "Food supplementation with an olive (Olea europaea L.) leaf extract reduces blood pressure in borderline hypertensive monozygotic twins". Phytotherapy Research 22 (9): 1239–1242. doi:10.1002/ptr.2455.
- Mohagheghi et al. The neuroprotective effect of olive leaf extract is related to improved blood–brain barrier permeability and brain edema in rat with experimental focal cerebral ischemia, 2011.
- Fakhraei, N.; Abdolghaffari, A. H.; Delfan, B.; Abbasi, A.; Rahimi, N.; Khansari, A.; Rahimian, R.; Dehpour, A. R. (2014). "Protective Effect of Hydroalcoholic Olive Leaf Extract on Experimental Model of Colitis in Rat: Involvement of Nitrergic and Opioidergic Systems". Phytotherapy Research 28 (9): 1367. doi:10.1002/ptr.5139.
- Hassanzadeh, K.; Akhtari, K.; Hassanzadeh, H.; Zarei, S. A.; Fakhraei, N.; Hassanzadeh, K. (2014). "The role of structural CH compared with phenolic OH sites on the antioxidant activity of oleuropein and its derivatives as a great non-flavonoid family of the olive components: A DFT study". Food Chemistry 164: 251–8. doi:10.1016/j.foodchem.2014.05.015. PMID 24996331.
- Dr Stevenson, L,. et al. Oxygen Radical Absorbance Capacity (ORAC) Report on Olive Leaf Australia's Olive Leaf Extracts, Southern Cross University, 2005.
- Saija et al. In vitro evaluation of the antioxidant activity and biomembrane interaction of the plant phenols oleuropein and hydroxytyrosol, 1998.
- Briante et al. Olea europaea L. leaf extract and derivatives: antioxidant properties, 2002.
- Speroni et al. Oleuropein Evaluated In Vitro and In Vivo as an Antioxidant, 1998.
- Pinelli et al. Quali-quantitative analysis and antioxidant activity of different polyphenolic extracts from Olea europea L. leaves, 2000.
- Hamdi et al. Oleuropein, a non-toxic olive iridoid, is an anti-tumor agent and cytoskeleton disruptor, 2005.
- Dr Stevenson, L,. et al. In vitro Biological Activities of Pure Olive Leaf Extract & High Strength Olive Leaf Extract, 2006.
- Muneer Abuismail. Analysis and Biological Evaluation of Jordanian Olive Trees Leaves - Cancer Cure Invention With Tissue Repair Potential, 2011.
- De Bock, M.; Derraik, J. G. B.; Brennan, C. M.; Biggs, J. B.; Morgan, P. E.; Hodgkinson, S. C.; Hofman, P. L.; Cutfield, W. S. (2013). Nerurkar, Pratibha V, ed. "Olive (Olea europaea L.) Leaf Polyphenols Improve Insulin Sensitivity in Middle-Aged Overweight Men: A Randomized, Placebo-Controlled, Crossover Trial". PLoS ONE 8 (3): e57622. doi:10.1371/journal.pone.0057622. PMC 3596374. PMID 23516412.
- Natural Antioxidants, Antibacterials From Olive Leaf Extracts Used In Cosmetics, Pharmaceutical, And Food Industries Fuad Al-rimawi, Prof., Imad Odeh, Abdallah Bisher, Hiba Yateem, and Mohammad Taraweh Qatar Foundation Annual Research Conference Proceedings 2014, HBPP0116. http://www.qscience.com/doi/abs/10.5339/qfarc.2014.HBPP0116
- "Olive leaf extract exhibits antiviral activity against viral haemorrhagic septicaemia rhabdovirus (VHSV)"[full citation needed]
- Induction of Growth Inhibition and Differentiation of Human Leukemia HL-60 Cells by a Tunisian Gerboui Olive Leaf Extract