Olive leaf contains a substance called oleuropein, which breaks down in the body to another substance called enolinate. On websites that promote olive leaf extracts, it is stated that enolinate kills harmful bacteria, viruses, and fungi in the body, but at the same time nurtures microbes that are good for health. This remarkable claim, however, has no meaningful scientific evidence.
It is true that oleuropein, enolinate, and other olive leaf constituents or their breakdown products can kill microbes in test-tube studies . 1-11 However, it is a long way from test-tube studies to evidence of efficacy in humans. Only double-blind , placebo-controlled studies can prove a treatment effective.
In addition to the claim that olive leaf can kill harmful substances in the body, proponetns also advocate its use to reduce blood pressure . Test-tube and animal studies have produced some positive preliminary findings. 13-16 And a small study did find evidence to support this, but there were flaws in its design. 12 A more recent, larger study offers more promising news, though. Two hundred and thirty-two people (aged 25-60) with high blood pressure were randomized to receive olive leave extract (500 mg, twice daily) or a commonly used anti-hypertensive medication called captopril (12.5 mg, twice daily) for a total of 8 weeks. Both treatment groups experienced similar reductions in blood pressure levels.
Olive leaf has also been studied as a potential treatment for other conditions. For example, animal studies weakly suggest that olive leaf might help control blood sugar levels in diabetes17-19 and reduce symptoms of gout . 17
Olive leaf has not undergone comprehensive safety testing. However, based on the limited evidence available, it does not appear to commonly cause much more in the way of immediate side effects than occasional digestive distress. Safety in young children, pregnant or nursing women, or people with severe liver or kidney disease has not been established.
8. Lee-Huang S, Zhang L, Huang PL, Chang YT, Huang PL. Anti-HIV activity of olive leaf extract (OLE) and modulation of host cell gene expression by HIV-1 infection and OLE treatment. Biochem Biophys Res Commun . 2003;307:1029–37.
13. Fehri B, Aiache JM, Memmi A, Korbi S, Yacoubi MT, Mrad S, Lamaison JL. Hypotension, hypoglycemia and hypouricemia recorded after repeated administration of aqueous leaf extract of Olea europaea L. J Pharm Belg . 1994;49:101–8.
14. Khayyal MT, el-Ghazaly MA, Abdallah DM, Nassar NN, Okpanyi SN, Kreuter MH. Blood pressure lowering effect of an olive leaf extract ( Olea europaea ) in L-NAME induced hypertension in rats. Arzneimittelforschung . 2002;52:797–802.
15. Ribeiro Rde A, Fiuza de Melo MM, De Barros F, Gomes C, Trolin G. Acute antihypertensive effect in conscious rats produced by some medicinal plants used in the state of Sao Paulo. J Ethnopharmacol . 1986;15:261–9.
17. Fehri B, Aiache JM, Memmi A, et al. Hypotension, hypoglycemia and hypouricemia recorded after repeated administration of aqueous leaf extract of Olea europaea L [in French]. J Pharm Belg . 199449:101–8.
19. Onderoglu S, Sozer S, Erbil KM, Ortac R, Lermioglu F. The evaluation of long-term effects of cinnamon bark and olive leaf on toxicity induced by streptozotocin administration to rats. J Pharm Pharmacol . 1999;51:1305–12.
Last reviewed December 2015 by EBSCO CAM Review Board
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