METHODOLOGY: The Cochrane central register of controlled trials, Medline (1966 to April week 1, 2020), Embase (1966 to April week 1, 2020) and trial registries for relevant randomized clinical trials were used. Published and unpublished randomized clinical trials were reviewed and evaluated. Random effects models were used to estimate the continuous outcomes and mean differences (MDs); both with 95% confidence intervals (CIs). The primary outcomes were changes in systolic and diastolic BP. The secondary outcomes were changes in lipid profile, glucose metabolism, inflammatory markers for CVD, kidney and liver functions safety parameters. We assessed the data for risk of bias, heterogeneity, sensitivity, reporting bias and quality of evidence.

RESULTS: Five trials were included involving 325 patients aged 18-80 years. Two trials involved high-income countries and three trials involved moderate-income countries. The analysis performed was based on three comparisons. No significant changes were found between systolic or diastolic blood pressure (BP) for the first comparison, 1,000 mg per day for a combined formulation of olive leaf extract versus a placebo. The second comparison, 500 mg per day of olive leaf extract versus placebo or no treatment, showed a significant reduction in systolic BP over a period of at least 8 weeks of follow up (MD -5.78 mmHg, 95% CI [-10.27 to -1.30]) and no significant changes on diastolic BP. The third comparison, 1,000 mg per day of olive leaf extract versus placebo shows no significant difference but an almost similar reduction in systolic BP (-11.5 mmHg in olive leaf extract and -13.7 mmHg in placebo, MD 2.2 mmHg, 95% CI [-0.43-4.83]) and diastolic BP (-4.8 mmHg in olive leaf extract and -6.4 mmHg in placebo, MD 1.60 mmHg, 95% CI [-0.13-3.33]). For secondary outcomes, 1,000 mg per day of olive leaf extract versus captopril showed a reduction in LDL (MD -6.00 mg/dl, 95% CI [-11.5 to -0.50]). The 500 mg per day olive leaf extract versus placebo showed a reduction in inflammatory markers for CVD IL-6 (MD -6.83 ng/L, 95% CI [-13.15 to -0.51]), IL-8 (MD -8.24 ng/L, 95% CI [-16.00 to -0.48) and TNF-alpha (MD -7.40 ng/L, 95% CI [-13.23 to -1.57]).

CONCLUSIONS: The results from this review suggest the reduction of systolic BP, LDL and inflammatory biomarkers, but it may not provide a robust conclusion regarding the effects of olive leaf extract on cardiometabolic profile due to the limited number of participants in the included trials.