Olea includes about thirty species of Old World trees. The only one of these native to Europe is O. europaea, which is also widespread in Africa. It is a variable and taxonomically complicated species. The latest treatment recognizes six subspecies. All cultivated material belongs to O. europaea subsp. europaea, which produces the best fruits. The olive fruit is a drupe with an oily, fleshy layer surrounding a central stone. Olives have for millennia been of great economic value in the Mediterranean area, as they may be either eaten or pressed for oil which in modern times is used primarily for cooking (and sometimes drunk by the glass in regional culinary tradition). Ripe olives are blackish; green olives are picked before they are completely ripe. Numerous varieties of olives are grown. Olive trees are also ornamental; the leaves have an unusual silvery coating of round, stalked umbrella-like scales on the lower surface. Olive pollen causes rhinitis in some hay fever sufferers.

In both Europe and Africa, tea made from the leaves is traditionally used to treat high blood pressure. Animal studies have demonstrated antihypertensive, vasodilatory, and anti-arrhythmic effects of crude olive leaf extract or of multiple constituent compounds. However, there has been only one very small human study to date; further research certainly seems called for. Culinary use of virgin olive oil is a major component of the traditional ?Mediterranean diet,? which has been proven to reduce heart disease risk and is correlated in epidemiological studies with lower rates of several other chronic diseases. Olive oil consists mainly of monounsaturated fatty acids, which have a variety of health benefits; virgin olive oil also contains high quantities of several antioxidant compounds, such as squalene, which has been shown in animal studies to reduce the risk of cancer. Regular consumption of olive oil may also reduce the risk of other health problems involving inflammation, such as rheumatoid arthritis.

Selected References

Alarcon de la Lastra, C., M. D. Barranco, V. Motilva, and J. M. Herrerias. 2001. Mediterranean diet and health: biological importance of olive oil. Curr. Pharm. Des. 7:933-950.

Cherif, S., N. Rahal, M. Haouala, B. Hizaoui, F. Dargouth, M. Gueddiche, Z. Kallel, G. Balansard, and K. Boukef. 1996. [A clinical trial of a titrated Olea extract in the treatment of essential arterial hypertension.] J. Pharm. Belg. 51:69-71.

Green, P. S. 2002. A revision of Olea L. (Oleaceae). Kew Bull. 57:91-140.

Green, P. S., and G. E. Wickens. 1989 The Olea europaea complex. Pp. 287-299 in: K. Tan, ed. The Davis & Hedge Festschrift. Edinburgh University Press: Edinburgh.

Khayyal, M. T., M. A. el-Ghazaly, D. M. Abdallah, N. N. Nassar, S. N. Okpanyi, and M. H. Kreuter. 2002. Blood pressure lowering effect of an olive leaf extract (Olea europaea) in L-NAME induced hypertension in rats. Arzneimittelforschung 52:797-802.

Newmark, H. L. 1999. Squalene, olive oil, and cancer risk. Review and hypothesis. Ann. N. Y. Acad. Sci. 889:193-203.

Panagiotakos, D. B., C. Pitsavos, E. Polychronopoulos, C. Chrysohoou, A. Zampelas, and A. Trichopoulou. 2004. Can a Mediterranean diet moderate the development and clinical progression of coronary heart disease? A systematic review. Med. Sci. Monit. 10:RA193-198.

Perez-Jiminez, F. 2005. International conference on the healthy effect of virgin olive oil. Eur. J. Clin. Invest. 35:421-424.

Somova, L. I., F. O. Shode, P. Ramnanan, and A. Nadar. 2003. Antihypertensive, antiatherosclerotic and antioxidant activity of triterpenoids isolated from Olea europaea, subspecies africana leaves. J. Ethnopharmacol. 84:299-305.

Somova, L. I., F. O. Shode, and M. Mipando. 2004. Cardiotonic and antidysrhythmic effects of oleanolic and ursolic acids, methyl maslinate and uvaol. Phytomedicine 11:121-129.