Olive leaf extract effect on cardiometabolic risk factors: a systematic review and meta-analysis of randomized clinical trials

CONTEXT: Olive leaf extract (OLE) is rich in phenolic compounds, which are known for their health benefits. Cardiovascular diseases, primarily coronary heart disease and stroke, are leading causes of mortality globally. OBJECTIVE: This systematic review aimed to assess the impact of OLE on cardiometabolic risk factors in adults. The selection of studies was based on intervention and outcomes, using relevant search descriptors. DATA SOURCES: The databases PubMed, EMBASE, and Web of Science were systematically searched for pertinent studies published up to August 2021. DATA EXTRACTION: Only randomized clinical trials, either cross-over or parallel, involving adult individuals aged ≥18 years, were considered. Additionally, trials that had a comparative or placebo group and used pure OLEs for oral treatment were included. DATA ANALYSIS: Twelve randomized clinical trials (RCTs) met the inclusion criteria. These trials had follow-up periods ranging from 2 days to 12 weeks and involved 703 patients aged 18 years-79 years. The outcomes demonstrated a positive correlation between the intervention group and glucose metabolism (4 RCTs), blood pressure (2 RCTs), lipid profile (2 RCTs), and inflammatory markers (2 RCTs). The RoB2 tool and the GRADE system were used to evaluate the risk of bias and the quality of evidence in the studies. CONCLUSIONS: In the meta-analysis, fasting glycemia, as evaluated in studies using a low dose of OLE, showed a significant result favoring the control group. To obtain more consistent results, further clinical studies in humans, using similar methodologies, are required. SYSTEMATIC REVIEW REGISTRATION: PROSPERO registration no. CRD42020200877.