Cardiovascular diseases are still a major cause of debilitation and mortality in industrial countries and hypertension is one of the main risk factors. In southern Europe, olive leaves have been traditionally used to treat hypertension. Oleuropein is a phenolic compound extracted from olive leaves and has manifested considerable antioxidant activity in vitro and in vivo. Also, it has been demonstrated that the polyphenols in olive have good bioavailability, which is compatible with their antioxidant effects.
In rats, administration of triterpenoids isolated from olive leaves with a dose of 60 mg/kg for 6 weeks, prevented the progress of hypertension and severe atherosclerosis and improved insulin resistance.(2) Furthermore, the triterpenoids isolated from olive leaves called oleanolic acid, ursolic acid, uvaol and methyl maslinate manifested little toxicity in brine shrimp test and have manifested considerable dose-dependent vasodepressor and sinus bradychardial effects; these effects being more prominent in the cases of oleanolic acid and methyl maslinate. These compounds act as beta-adrenergic antagonists and block the effect of adrenaline and isoprenaline. The demonstrated positive inotropic and dromotropic effects have also been more distinctive in the case of oleanolic acid and methyl maslinate. Oleanolic acid and ursolic acid have shown anti-dysrhythmic effects on chemical arrhythmias caused by CaCl2 and adrenaline and ischemia-reperfusion arrhythmias, which is comparable to the effects of propranolol and is indicative of beta-adrenergic antagonistic effects.
In a survey of the effects of various extracts of 9 vasoactive medicinal plants on contractions of aortic strips caused by K+ depolarization, olive extract has shown obvious effects and a comparison between contractions caused by K+ and norepinephrine showed that olive leaf is an antagonist of Ca++.
Based on research, olive leaf extract causes vasodilatation, bradycardia and negative inotropic effect and probably retardation of atrioventricular conduction in isolated rabbit heart. Also, olive leaf extract causes a reduction in contraction-related systolic pressure in the left ventricle. Researchers have come to the conclusion that olive leaf extract directly and reversibly suppresses L-type calcium channels.
In rats, olive leaf extract (EFLA®943) has had anti-hypertensive effects. In an open study, monozygotic twins with border-line hypertension were randomly divided into various treatment groups. Each group consisted of 10 patients. It was recommended to the participants to either take 500 or 100 mg of this extract daily as a dietary supplement for 8 weeks, or adhere to a healthy lifestyle. Every 2 weeks, weight, blood pressure, blood sugar and lipids were measured. After 8 weeks, in the control group and in the group taking the lower dose of the extract, mean blood pressure remained unchanged in comparison to the beginning of the study, but there existed considerable reduction in blood pressure in the group taking the higher dose of the extract. The considerable reduction was observed in relation to the prescribed dosage. In comparison with the control group, in the group taking 500 mg of the extract, the difference between mean systolic pressure was less or equal to 6 mm Hg. This difference was less or equal to 13 mm Hg in the group taking 1000 mg of the extract. The difference in the diastolic pressure was reported as less or equal to 5 mm Hg. In both treatment groups, cholesterol level showed considerable decline. In case of LDL, the difference between twins in the two treatment groups was dependent on dose and was statistically significant. This study proved the efficacy of olive leaf extract in reduction of blood pressure and cholesterol.
In a survey of the effects of various doses of lyophilized aqueous extract of olive leaf on rat thyroid function, this extract has shown to have stimulant effects on the thyroid, independent from the pituitary gland. This effect might explain the hypolipidemic effect of olive leaf, because with an increase in the thyroid hormones in the circulation, the level of serum lipids including cholesterol decreases. Also, the fact that an increase in thyroid function results in reduction of blood sugar is indicative of hypoglycemic effects of olive leaf.
In an study on healthy rats and streptozotocin-induced diabetic rats, oral administration of olive leaf extract with doses of 0.1, 0.25 and 0.5 g/kg body weight of the animal for 14 days, considerably decreased blood sugar, total cholesterol, triglyceride, urea, uric acid, creatinine, AST and ALT, but increased serum insulin only in diabetic rats (p<0.05). Also, in comparison with glibenclamide (600 μg/kg), the antidiabetic effect of olive leaf extract was more efficient than glibenclamide.