Olive (Olea europaea L.) Leaf Polyphenols Improve Insulin Sensitivity in Middle-Aged Overweight Men: A Randomized, Placebo-Controlled, Crossover Trial
What this study found
Olive leaf polyphenol supplementation improved insulin sensitivity and pancreatic beta-cell secretory capacity, but it did not produce consistent benefits for other cardiovascular risk factors. The Matsuda index improved to 5.46 with olive leaf extract versus 4.73 with placebo after 12 weeks, a 15% improvement, p = 0.024. Disposition index improved to 5.45 versus 4.26, a 28% improvement, p = 0.013. Glucose AUC decreased 6% (p = 0.008) and insulin AUC decreased 14% (p = 0.041), with reductions in glucose at 30 minutes and 60 minutes and insulin at 60 minutes. No significant changes were seen…
- Study & population
- Randomized, double-blind, placebo-controlled crossover trial in overweight middle-aged men at risk of metabolic syndrome in the Auckland region of New Zealand.
- Intervention
- Olive leaf extract was given orally as four capsules once daily for 12 weeks, providing 51.1 mg oleuropein and 9.7 mg hydroxytyrosol per day.
- Key limitation
- The trial was small, short term, and limited to overweight middle-aged men, which restricts generalizability.
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Open PDFOriginal 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/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. 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. Trial Registration Australian New Zealand Clinical Trials Registry #336317.