This is meant to be a brief summary of the effects of olive leaf extracts. I have written about this topic in the past so not all of the material is brand new. If you have any detailed questions, feel free to ask.
Olive leaf
History
Olive Leaf extracts are all the rage in supplements now, and for good reason. Olive leaves have been used in the human diet as a food and as well as in traditional remedies in Mediterranean countries for hundreds of years. Olive leaf has been found to contain multiple antioxidants that have promising pro-health benefits (1). All parts of the olive tree have been known and used for the nutritious and medicinal properties (2).
Effects
Olive leaf extracts contain many different phenols. Oleuropein is a phenylethanoid present in Olive Leaf extract that possesses powerful antioxidant properties. Another interesting component of olive leaf extract is Hydroxytyrosol, but that is potentially the focus of another article so I won’t elaborate much on it here.
There is no clear consensus as of now whether Olive Leaf extracts truly lower blood pressure as studies tend to differ in their results. Olive leaf extracts have been shown to improve insulin sensitivity in humans. Oleuropein has also been shown to potentially aid in fat loss by increasing thermogenin in brown adipose tissue (3-6).
A recent study has examined human absorption of oleuropein in humans, and has found that Olive Leaf extracts effectively deliver oleuropein metabolites to plasma in humans (7). Oleuropein is an in vitro PPAR γ inhibitor in adipocytes but the dose required for this in humans would be rather large (8). A very curious study in rats shows that oleuropein increased norepinephrine and testosterone levels, decreased corticosterone levels, and increased nitrogen balance (9).
Another interesting property of oleuropein is that it has been found to increase thyroid activity in rats (10).
As you can note, the decrease in TSH (which means an increase in thyroid activity) is statistically significant. At the higher doses, the increase in T3 was statistically significant, but the increase in T4 was not statistically significant. Individuals with any history of thyroid disease should not supplement with olive leaf extracts.
Two studies showed no weight loss from subjects supplementing with olive leaf extract, but these studies did not specify the oleuropein or hydroxytyrosol content. It is possible they did not observe significant weight loss since they did not use a specialized extract for either of these two compounds (11-12).
Toxicity
In one study, rats given a dose of 60 mg/kg saw no toxicity (13). This is equivalent to approximately 1,000 mg for a 100 kg human (13). In one human clinical trial doses as high as 1000 mg per day were used on adults between 18 and 60 years of age with no adverse effects (14).
Summary
Olive leaf extracts have a host of benefits to them, including increasing insulin sensitivity, increasing thyroid activity, antioxidant benefits, and many more. Olive leaf phenols are currently the subject of investigation for Alzheimer’s disease (15).
References
1. Sedef N El, Sibel Karakaya. (2009). Olive tree (Olea europaea) leaves: potential beneficial effects on human health. Nutrition Reviews. Volume 67, Issue 11, pages 632–638.
2. Soni MG, Burdock GA, Christian MS, Bitler CM, Crea R. (2006). Safety assessment of aqueous olive pulp extract as an antioxidant or antimicrobial agent in foods. Food Chem Toxicol. 44:903–915.
3. 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). "Olive (Olea europaea L.) Leaf Polyphenols Improve Insulin Sensitivity in Middle-Aged Overweight Men: A Randomized, Placebo-Controlled, Crossover Trial". In Nerurkar, Pratibha V. PLoS ONE 8 (3): e57622.
4. Sudjana, Aurelia N.; D’Orazio, Carla; Ryan, Vanessa; Rasool, Nooshin; Ng, Justin; Islam, Nabilah; Riley, Thomas V.; Hammer, Katherine A. (2009). "Antimicrobial activity of commercial Olea europaea (olive) leaf extract". International Journal of Antimicrobial Agents 33 (5): 461–3. doi:10.1016/j.ijantimicag.2008.10.026. PMID 19135874.
5. Oi-Kano, Yuriko; Kawada, Teruo; Watanabe, Tatsuo; Koyama, Fumihiro; Watanabe, Kenichi; Senbongi, Reijirou; Iwai, Kazuo (2008). "Oleuropein, a Phenolic Compound in Extra Virgin Olive Oil, Increases Uncoupling Protein 1 Content in Brown Adipose Tissue and Enhances Noradrenaline and Adrenaline Secretions in Rats". Journal of Nutritional Science and Vitaminology 54 (5): 363–70.
6. Haris Omar, Syed (2010). "Oleuropein in Olive and its Pharmacological Effects". Scientia Pharmaceutica 78 (2): 133–54. doi:10.3797/scipharm.0912-18.
7. de Bock M, Thorstensen EB, Derraik JG, Henderson HV, Hofman PL, Cutfield WS (2013) Human absorption and metabolism of oleuropein and hydroxytyrosol ingested as olive (Olea europaea L.) leaf extract. Mol Nutr Food Res.
8. Svobodova, M., Andreadou, I., Skaltsounis, A.-L., Kopecky, J., & Flachs, P. (2014). Oleuropein as an inhibitor of peroxisome proliferator-activated receptor gamma. Genes & nutrition, 9(1), 376.
9. Oi-Kano, Y., Kawada, T., Watanabe, T., Koyama, F., Watanabe, K., Senbongi, R., & Iwai, K. (2013). Oleuropein supplementation increases urinary noradrenaline and testicular testosterone levels and decreases plasma corticosterone level in rats fed high-protein diet. Journal of Nutritional Biochemistry, 24(5), 887-893.
10. Al-Qarawi, A., Al-Damegh, M. a, & ElMougy, S. a. (2002). Effect of freeze dried extract of Olea europaea on the pituitary-thyroid axis in rats. Phytotherapy research : PTR, 16(3), 286-7.
11. Gimeno, E., de la Torre-Carbot, K., Lamuela-Raventos, R. et al. (2007). Changes in the phenolic content of low density lipoprotein after olive oil consumption in men. A randomized crossover controlled trial. Br J Nutr. 98(6):1243-50.
12. Castaner, O., Covas, M., Khymenets, O. et al. (2012). Protection of LDL from oxidation by olive oil polyphenols is associated with a downregulation of CD40-ligand expression and its downstream products in vivo in humans. Am J Clin Nut. 95(5):1238-44.
13. L.I. Somova et al. (2003). Antihypertensive, antiatherosclerotic and antioxidant activity of triterpenoids isolated from Olea europaea, subspecies africana leaves. Journal of Ethnopharmacology Volume 84, Issues 2–3, Pages 299–305.
14. Tania Perrinjaquet-Moccetti et al. (2008). Food Supplementation with an Olive (Olea europaeaL.) Leaf Extract Reduces Blood Pressure in Borderline Hypertensive Monozygotic Twins. Phytother. Res. 22, 1239–1242.
15. Rigacci, S. (2015). Olive Oil Phenols as Promising Multi-targeting Agents Against Alzheimer's Disease. Adv Exp Med Biol. 863:1-20.
