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

Martin De Bock,Philip E Morgan,Paul L Hofman,Christine M Brennan,Steven C Hodgkinson,Wayne S Cutfield,Janene B Biggs,José G B Derraik,Pratibha V Nerurkar

doi:10.1371/journal.pone.0057622

Martin De Bock, Philip E Morgan + Show 7 more

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https://doi.org/10.1371/journal.pone.0057622

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Abstract

BackgroundOlive 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.ObjectiveTo 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.DesignRandomized, double-blinded, placebo-controlled, crossover trial in New Zealand. 46 participants (aged 46.4±5.5 years and BMI 28.0±2.0 kg/m2) 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.ResultsTreatment 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.ConclusionsSupplementation 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.Trial RegistrationAustralian New Zealand Clinical Trials Registry #336317.

Highlights

It is estimated that 20–50% of the European population use complementary or alternative therapy to treat disease or to help prevent its onset [1]
olive leaf extract (OLE) supplementation was associated with a 15% improvement in insulin sensitivity (p = 0.024) compared to placebo
Four participants were on cholesterol lowering medication, three were on antihypertensives, and two were on both

Summary

Introduction

It is estimated that 20–50% of the European population use complementary or alternative therapy to treat disease or to help prevent its onset [1]. In Britain, approximately 40% of general practitioners provide complementary therapies for their patients [2]. With respect to type 2 diabetes, one third of patients actively use alternative medicine to manage their disease, despite the paucity of scientific evidence to support its use [3]. The leaves of the olive plant (Olea europaea L.) have been used for centuries in folk medicine to treat diabetes [4]. 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

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