Benefits
Cardiovascular markers: no change in the one cited trial
Oleuropein and hydroxytyrosol are the olive polyphenols people study for blood pressure and blood-vessel function, but the one trial cited here does not back that up. In 74 overweight adults who completed 8 weeks on 500 mg of olive leaf extract per day, blood pressure, total cholesterol, LDL, HDL and triglycerides were all no different from placebo.
Antioxidant marker: measured and unchanged
Hydroxytyrosol and oleuropein behave as antioxidants in laboratory work, but the trial cited here measured oxidized LDL in people and reported no statistically significant difference between the extract and placebo after 8 weeks. Protection of cells or LDL in the body has not been shown for this product.
Blood sugar and lipids: no effect found
Blood sugar and blood fats were measured directly in the one cited trial. Fasting glucose, insulin, total cholesterol, LDL, HDL and triglycerides all came back no different from placebo after 8 weeks. An outcome that was measured and came back flat is a result, not an open question.
Mechanism of action
Olive polyphenol action
In laboratory and animal work, oleuropein and hydroxytyrosol are proposed to help blood vessels relax through nitric oxide and to act as antioxidants. This is a proposed mechanism only. When it was tested in people in the one trial on this page, blood pressure and oxidized LDL did not change.
Anti-inflammatory action
Olive polyphenols reduce markers of oxidative and inflammatory stress in laboratory studies. No human trial cited on this page shows Berkemyol doing this in the body.
Clinical trials
Randomized, double-blind, placebo-controlled trial of 500 mg per day of olive leaf extract for 8 weeks. (Stevens et al. 2021, European Journal of Nutrition.) Important limits: the paper names no branded extract, it simply says "olive leaf extract", so this is not a test of Berkemyol; and one of the authors is an employee of BioActor BV, a different company.
77 overweight adults, average age about 56, with mildly raised cholesterol (5.0 to 8.0 mmol/l); 74 finished the study.
Nothing changed. Total cholesterol, LDL, HDL, triglycerides, oxidized LDL, blood pressure, fasting glucose, insulin and liver function tests were all no different from placebo (p greater than 0.05). This was a clean, adequately sized 8-week study, and it found no benefit.