Inflammation

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Reference: Schwingshackl, L., M. Christoph, and G. Hoffmann, Effects of Olive Oil on Markers of Inflammation and Endothelial Function-A Systematic Review and Meta-Analysis. Nutrients, 2015. 7(9): p. 7651-75.

One-sentence summary: Evidence from randomised controlled trials shows olive oil exerts beneficial effects on markers of inflammation and endothelial function.

Study type: A systematic review and meta-analysis of 28 RCTs on olive oil and markers of inflammation or endothelial function.

Diet: Diets containing olive oil (consumed in pure form or supplemented as capsules; ranging between approximately 1 g per capsule and 50 mL in pure form.)

Outcomes measured:

1. Markers of inflammation:

• C-reactive protein (CRP)
• interleukin-6 (IL-6)
• TNF-α
• adiponectin

1. Markers of endothelial function:

• intercellular adhesion molecule-1 (ICAM-1)
• vascular cell adhesion molecule-1 (VCAM-1)
• flow-mediated dilatation (FMD)

Population: Adult populations who consumed olive oil for at least 4 weeks, and authors did not specify country of origin. There was no exclusion for disease, and studies included subjects with a range of health conditions (e.g. healthy as well as Type 2 diabetes, chronic heart failure, persons with >1 coronary event) and medications.

Key results:

The olive oil intervention resulted in:

• Reduction in CRP: Mean difference = -0.64; 95% CI -0.96 to -0.31; P<0.0001 (15 studies)
• Reduction in IL-6: Mean difference = -0.29; 95% CI -0.7 to -0.02; P<0.04 (7 studies)
• Increase in FMD: Mean difference = 0.76; 95% CI 0.27 to 1.24; P<0.002 (8 studies)
• Reduction in sE-Selectin: Mean difference = -3.16; 95% CI -4.07 to -2.25; P<0.00001 (2 studies)
• No significant effect for TNF-α (5 studies)
• No significant effect for Adiponectin (6 studies)
• No significant effect for ICAM-1 (7 studies)
• No significant effect for VCAM-1 (8 studies)

Quality assessment: Most studies failed to provide enough information for a thorough assessment of bias analysis.

Limitations:

• There was considerable amount of heterogeneity between studies e.g., the length of intervention, amount and type of olive oil used, classification of control and the number of participants.
• Some studies prescribed the intake of olive oil in addition to a baseline Mediterranean diet that already consisted of olive oil, which means the absolute quantity of olive oil consumed could not be determined.

The bottom line: Markers of inflammation (CRP, IL-6) and endothelial function (FMD, sE-Selectin) were improved following interventions with olive oil. These markers are generally regarded to influence CVD risk and may help to explain the cardio-protective associations of olive oil in observational studies.

Other reviews:

Mayr, H.L., et al., Mediterranean-type diets and inflammatory markers in patients with coronary heart disease: a systematic review and meta-analysis. Nutr Res, 2018. 50: p. 10-24.

Schwingshackl, L. and G. Hoffmann, Mediterranean dietary pattern, inflammation and endothelial function: a systematic review and meta-analysis of intervention trials. Nutr Metab Cardiovasc Dis, 2014. 24(9): p. 929-39.

Ahluwalia, N., et al., Dietary patterns, inflammation and the metabolic syndrome. Diabetes Metab, 2013. 39(2): p. 99-110.

Barbaresko, J., et al., Dietary pattern analysis and biomarkers of low-grade inflammation: a systematic literature review. Nutr Rev, 2013. 71(8): p. 511-27.