Olive (Olea Europaea L.) Leaf Polyphenols Improve Insulin Sensitivity in Middle-Aged Overweight Men: A Randomized, Placebo-Controlled, Crossover Trial

PLoS One. 2013;8(3):e57622. doi: 10.1371/journal.pone.0057622. Epub 2013 Mar 13.

Abstract

Background: Olive plant leaves (Olea europaea L.) have been used for centuries in folk medicine to treat diabetes, but there are very limited data examining the effects of olive polyphenols on glucose homeostasis in humans.

Objective: To assess the effects of supplementation with olive leaf polyphenols (51.1 mg oleuropein, 9.7 mg hydroxytyrosol per day) on insulin action and cardiovascular risk factors in middle-aged overweight men.

Design: Randomized, double-blinded, placebo-controlled, crossover trial in New Zealand. 46 participants (aged 46.4 ± 5.5 years and BMI 28.0 ± 2.0 kg/m(2)) were randomized to receive capsules with olive leaf extract (OLE) or placebo for 12 weeks, crossing over to other treatment after a 6-week washout. Primary outcome was insulin sensitivity (Matsuda method). Secondary outcomes included glucose and insulin profiles, cytokines, lipid profile, body composition, 24-hour ambulatory blood pressure, and carotid intima-media thickness.

Results: Treatment evaluations were based on the intention-to-treat principle. All participants took >96% of prescribed capsules. OLE supplementation was associated with a 15% improvement in insulin sensitivity (p = 0.024) compared to placebo. There was also a 28% improvement in pancreatic β-cell responsiveness (p = 0.013). OLE supplementation also led to increased fasting interleukin-6 (p = 0.014), IGFBP-1 (p = 0.024), and IGFBP-2 (p = 0.015) concentrations. There were however, no effects on interleukin-8, TNF-α, ultra-sensitive CRP, lipid profile, ambulatory blood pressure, body composition, carotid intima-media thickness, or liver function.

Conclusions: Supplementation with olive leaf polyphenols for 12 weeks significantly improved insulin sensitivity and pancreatic β-cell secretory capacity in overweight middle-aged men at risk of developing the metabolic syndrome.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Blood Glucose / drug effects
  • Body Mass Index
  • Cross-Over Studies
  • Glucose / metabolism
  • Glucose Tolerance Test
  • Humans
  • Insulin Resistance*
  • Middle Aged
  • New Zealand
  • Olea / chemistry*
  • Overweight / drug therapy*
  • Overweight / metabolism*
  • Plant Extracts / chemistry
  • Plant Extracts / pharmacology
  • Plant Leaves / chemistry*
  • Polyphenols / pharmacology*
  • Polyphenols / therapeutic use*
  • Treatment Outcome

Substances

  • Blood Glucose
  • Plant Extracts
  • Polyphenols
  • Glucose

Grant support

This study was supported by a TECHNZ grant (University of Auckland - UniS 30475.001) through the New Zealand Ministry of Science and Innovation (MSI). TECHNZ grants are funded 50% by the MSI, and 50% by a commercial partner following an extensive independent science review process. In this project, the commercial partner was the olive leaf extract manufacturer (Comvita). MdB was funded by the Joan Mary Reynolds Trust. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.