Cardiovascular, Metabolic and Endocrine, Cancer, Mortality, Derma, and Other Outcomes of Olive Oil and Oleic Acid: An Umbrella Review

The research on health effects of olive oil and oleic acid remains variable. This umbrella review aimed to synthesize evidence from systematic reviews (with or without meta-analyses) regarding the health outcomes of oleic acid and olive oil, clarify the validity and strength of the evidence, and finally help to make dietary recommendations for different people. We conducted a comprehensive search of the Cochrane, PubMed, Web of Science, Medline, and Embase databases. These studies were assessed using AMSTAR 2 and GRADE tools. 19 out of 741 eligible studies were included, and the majority were prospective studies. Topical application of olive oil is suggested to prevent pressure ulcers and acute radiation dermatitis; only a few adverse reactions (e.g., occupational allergic contact dermatitis and lichen planus pigmentosus) have been reported. Consumption of olive oil reduced the risk of Type 2 diabetes and cardiovascular disease by 22% and 18%, respectively. Especially, olive oil improved glycemic control in reducing fasting blood glucose (MD: -0.44, 95% CI: -0.66, -0.22), HbA1c (MD = -0.27, 95% CI: -0.37, -0.17), insulin (SMD = -0.28, 95% CI: -0.51, -0.05), and homeostatic model assessment for insulin resistance (HOMA-IR) (SMD = -0.19, 95% CI: -0.35, -0.03). Every 25 g/day OO intake was associated with an 11% lower relative risk of all-cause mortality (95% CI: 0.85, 0.93). Additionally, each 10 g/day olive oil intake increased 0.22 mg/dL HDL and improved endothelial function. However, the quality of 77% of the evidence was low to moderate, as assessed by GRADE. The methodological quality of 69% of the studies was low and critically low. Olive oil is proven to be a healthy dietary option for Type 2 diabetes and cardiovascular disease populations, a superior topical application choice for the immobilized. With the major evidence not being high, further standardized research is needed to explore the optimal dosage and the effects of oleic acid in olive oil.