The effects of olive leaf extract on cardiovascular risk factors in the general adult population: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND: The aim of this systematic review and meta-analysis was to determine the effect of olive leaf extract (OLE) supplementation on cardiovascular-related variables, including lipid, glycemic, inflammatory, liver and renal-related factors, as well as blood pressure. METHODS: PubMed, ISI Web of Science, Scopus, and Cochrane library were searched, up to October 2021, for relevant controlled trials. Mean differences and standard deviations were pooled for all outcomes, using a random-effects model. The methodological quality, as well as quality of evidence were assessed using standard tools. RESULTS: Twelve studies (n = 819 participants) were included in our analyses. Overall analyses showed that OLE supplementation significantly decreased triglyceride (TG) levels (WMD = − 9.51 mg/dl, 95% CI − 17.83, − 1.18; P = 0.025; I(2) = 68.7%; P-heterogeneity = 0.004), and systolic blood pressure (SBP) (WMD = − 3.86 mmHg, 95% CI − 6.44, − 1.28 mmHg; P = 0.003; I(2) = 19.9%; P-heterogeneity = 0.28). Subgroup analyses also revealed a significant improvement in SBP (− 4.81 mmHg) and diastolic blood pressure (− 2.45 mmHg), TG (− 14.42 mg/dl), total cholesterol (TC) (− 9.14 mg/dl), and low-density lipoprotein-C (LDL-C) (− 4.6 mg/dl) measurements, in patients with hypertension. Significant reductions were also observed in TC (− 6.69 mg/dl), TG (− 9.21 mg/dl), and SBP (− 7.05 mmHg) in normal-weight individuals. However, no meaningful changes were seen in glucose hemostasis, liver and kidney, or inflammatory markers. CONCLUSION: The present study revealed that supplementation with OLE yielded beneficial effects for blood pressure and lipid profile in adults, especially in patients with hypertension. As the quality of evidence for glucose hemostasis variables, liver, kidney, and inflammatory markers, were low-to-very low, higher quality RCTs may impact the overarching results. This study was registered at PROSPERO with the code CRD42022302395. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13098-022-00920-y.