Monograph. Olive leaf. Altern Med Rev. 2009;14(1): 62-66.
Olive leaf components in vitro inhibit many viruses, e.g.
pseudorabies, some forms of polio, cold and influenza viruses, and human
immunodeficiency virus (HIV). One constituent, calcium elenolate, inhibited
nearly every virus studied, including coxsackie, encephalitis, and two strains
OLE inhibits many gram-negative and gram-positive bacteria, yeasts, and parasites, including malaria-causing Plasmodium falciparum. It may inactivate cellular enzymes needed for replication, or directly attack bacterial cell walls. Clinical trials have not evaluated olive leaf against bacterial pathogens. It inhibits food-borne Bacillus cereus in vitro and in humans, altering germinating spores to delay growth. In vivo, in multi-drug resistant Pseudomonas aeruginosa, oleuropein reduced oxidative stress and prolonged survival.
OLE was reported to be hypotensive in 1951. It suppresses the L-type calcium channel directly and indirectly, causing vasodilation and reducing blood pressure. Oleuropein individually is also a vasodilator. OLE is antioxidant and anti-inflammatory. It had the highest radical-scavenging ability of 55 medicinal herbs in one study, more than twice that of green tea (Camellia sinensis) or milk thistle (Silybum marianum). Oleuropein reduces oxidation of low-density lipoprotein (LDL) in vitro and in vivo. OLE inhibits platelet aggregation and thromboxane A2 production. All of these effects contribute to olive leaf's cardiovascular benefits, as do its hypoglycemic effects. Given to rats with induced diabetes, it reduced blood glucose levels significantly, raised insulin levels, and increased peripheral glucose uptake dose-dependently. OLE components luteolin and oleanolic acid inhibited postprandial glucose increase in vivo. OLE given to hypertensive rats at 100-1000 mg/kg for 2-6 weeks significantly lowered mean arterial pressure and heart rate. Given to salt-sensitive, genetically hypertensive rats at 60 mg/kg, it prevented severe hypertension and atherosclerosis (most likely by suppressing inflammation) and improved insulin resistance.
A human clinical trial studied OLE's effects on blood pressure in 40 borderline hypertensive pairs of identical twins. Twins from each pair were assigned to control or to one of two groups receiving 500 or 1000 mg/d OLE for six weeks. Mean blood pressure was unchanged for control and 500 mg groups, but the 1000 mg group had a significant decrease in mean systolic blood pressure (from 137 +/- 10 to 126 +/- 6; P<0.01). Another clinical trial (n=30) reported significant decreases in blood pressure in hypertensive patients given 400 mg aqueous OLE four times/d for three months. In vitro, olive leaf polyphenols significantly suppressed platelet-ATP release and platelet aggregation in a dose-dependent manner.
In vivo, OLE in doses of 100, 250, and 500 mcg/d increased T3 levels dose-dependently and significantly reduced circulating thyroid stimulating hormone after 14 days, suggesting a possible use in hypothyroidism.
Due to OLE's hypotensive and antiplatelet aggregation effects, caution should be used if also using blood pressure lowering or blood thinning medicines. In vivo studies report no toxicity even at high doses; studies in human cell lines likewise have found no toxicity. No studies have been undertaken in pregnancy or lactation. OLE is best taken with food to avoid gastrointestinal irritation.