Dietary oleic acid supplementation and blood inflammatory markers: a systematic review and meta-analysis of randomized controlled trials

The aim of this systematic review and meta-analysis was to analyze data from randomized controlled trials (RCTs) assessing the effects of oleic acid (OA) supplementation on blood inflammatory markers in adults. PubMed, EMBASE and Cochrane Library databases were systematically searched from 1950 to 2019, with adults and a minimum intervention duration of 4 weeks. The effect size was estimated, adopting standardized mean difference (SMD) and 95% confidence interval (CI). Of the 719 identified studies, thirty-one RCTs involving 1634 subjects were eligible. The results of this study revealed that increasing OA supplementation significantly reduced C-reactive protein (CRP) (SMD: -0.11, 95% CI: -0.21, -0.01, P = 0.038). However, dietary OA consumption did not significantly affect tumor necrosis factor (TNF) (SMD: -0.05, 95% CI: -0.19, 0.10, P = 0.534), interleukin 6 (IL-6) (SMD: 0.01, 95% CI: -0.10, 0.13, P = 0.849), fibrinogen (SMD: 0.08, 95% CI: -0.16, 0.31, P = 0.520), plasminogen activator inhibitor type 1 (PAI-1) activity (SMD: -0.11, 95% CI: -0.34, 0.12, P = 0.355), soluble intercellular adhesion molecule-1 (sICAM-1) (SMD: -0.06, 95% CI: -0.26, 0.13, P = 0.595) or soluble vascular cell adhesion molecule-1 (sVCAM-1) (SMD: -0.04, 95% CI: -0.27, 0.18, P = 0.701). Overall, the meta-analysis demonstrated that dietary OA supplementation significantly reduced CRP, yet did not affect other inflammatory markers including TNF, IL-6, fibrinogen, PAI-1 activity, sICAM-1or sVCAM-1.